Metformin Hydrochloride (metformin hydrochloride 500 mg) Dailymed
Generic: metformin hydrochloride
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WARNINGS Lactic Acidosis: are generally found. The reported incidence of lactic acidosis in patients receiving metformin hydrochloride is very low (approximately 0.03 cases/1000 patient-years, with approximately 0.015 fatal cases/1000 patient-years). In more than 20,000 patient-years exposure to metformin in clinical trials, there were no reports of lactic acidosis. Reported cases have occurred primarily in diabetic patients with significant renal insufficiency, including both intrinsic renal disease and renal hypoperfusion, often in the setting of multiple concomitant medical/surgical problems and multiple concomitant medications. Patients with congestive heart failure requiring pharmacologic management, in particular those with unstable or acute congestive heart failure who are at risk of hypoperfusion and hypoxemia, are at increased risk of lactic acidosis. The risk of lactic acidosis increases with the degree of renal dysfunction and the patient's age. The risk of lactic acidosis may, therefore, be significantly decreased by regular monitoring of renal function in patients taking metformin hydrochloride tablets or metformin hydrochloride extended-release tablets and by use of the minimum effective dose of metformin hydrochloride tablets or metformin hydrochloride extended-release tablets. In particular, treatment of the elderly should be accompanied by careful monitoring of renal function. Metformin hydrochloride tablets or metformin hydrochloride extended-release tablets treatment should not be initiated in patients80 years of age unless measurement of creatinine clearance demonstrates that renal function is not reduced, as these patients are more susceptible to developing lactic acidosis. In addition, metformin hydrochloride tablets and metformin hydrochloride extended-release tablets should be promptly withheld in the presence of any condition associated with hypoxemia, dehydration, or sepsis. Because impaired hepatic function may significantly limit the ability to clear lactate, metformin hydrochloride tablets and metformin hydrochloride extended-release tablets should generally be avoided in patients with clinical or laboratory evidence of hepatic disease. Patients should be cautioned against excessive alcohol intake, either acute or chronic, when taking metformin hydrochloride tablets or metformin hydrochloride extended-release tablets, since alcohol potentiates the effects of metformin hydrochloride on lactate metabolism. In addition, metformin hydrochloride tablets and metformin hydrochloride extended-release tablets should be temporarily discontinued prior to any intravascular radiocontrast study and for any surgical procedure (see alsoPRECAUTIONS). The onset of lactic acidosis often is subtle, and accompanied only by nonspecific symptoms such as malaise, myalgias, respiratory distress, increasing somnolence, and nonspecific abdominal distress. There may be associated hypothermia, hypotension, and resistant bradyarrhythmias with more marked acidosis. The patient and the patient's physician must be aware of the possible importance of such symptoms and the patient should be instructed to notify the physician immediately if they occur (see alsoPRECAUTIONS). Metformin hydrochloride tablets and metformin hydrochloride extended-release tablets should be withdrawn until the situation is clarified. Serum electrolytes, ketones, blood glucose and, if indicated, blood pH, lactate levels, and even blood metformin levels may be useful. Once a patient is stabilized on any dose level of metformin hydrochloride tablets or metformin hydrochloride extended-release tablets, gastrointestinal symptoms, which are common during initiation of therapy, are unlikely to be drug related. Later occurrence of gastrointestinal symptoms could be due to lactic acidosis or other serious disease. Levels of fasting venous plasma lactate above the upper limit of normal but less than 5 mmol/L in patients taking metformin hydrochloride tablets or metformin hydrochloride extended-release tablets do not necessarily indicate impending lactic acidosis and may be explainable by other mechanisms, such as poorly controlled diabetes or obesity, vigorous physical activity, or technical problems in sample handling. (See alsoPRECAUTIONS.) Lactic acidosis should be suspected in any diabetic patient with metabolic acidosis lacking evidence of ketoacidosis (ketonuria and ketonemia). Lactic acidosis is a medical emergency that must be treated in a hospital setting. In a patient with lactic acidosis who is taking metformin hydrochloride tablets or metformin hydrochloride extended-release tablets, the drug should be discontinued immediately and general supportive measures promptly instituted. Because metformin hydrochloride is dialyzable (with a clearance of up to 170 mL/min under good hemodynamic conditions), prompt hemodialysis is recommended to correct the acidosis and remove the accumulated metformin. Such management often results in prompt reversal of symptoms and recovery. (See alsoCONTRAINDICATIONSandPRECAUTIONS.)
Description
Metformin hydrochloride tablets and metformin hydrochloride extended-release tablets are oral antihyperglycemic drugs used in the management of type 2 diabetes. Metformin hydrochloride (N,N-dimethylimidodicarbonimidic diamide hydrochloride) is not chemically or pharmacologically related to any other classes of oral antihyperglycemic agents. The structural formula is as shown:Metformin hydrochloride is a white to off-white crystalline compound with a molecular formula of C4H11N5and a molecular weight of 165.63. Metformin hydrochloride is freely soluble in water and is practically insoluble in acetone, ether and chloroform. The pKa of metformin is 12.4. The pH of a 1% aqueous solution of metformin hydrochloride is 6.68. Metformin hydrochloride tablets contain 500 mg, 850 mg, or 1000 mg of metformin hydrochloride. Each tablet contains the inactive ingredients magnesium stearate, microcrystalline cellulose and povidone. In addition, the coating for the 500 mg, 850 mg and 1000 mg tablets contains hypromellose 2910, polyethylene glycol 400 and titanium dioxide. Metformin hydrochloride extended-release tablets contain 500 mg or 750 mg of metformin hydrochloride as the active ingredient. Metformin hydrochloride extended-release 500 mg tablets contain the inactive ingredients hypromellose 2208, colloidal silicon dioxide, and magnesium stearate. Metformin hydrochloride extended-release 750 mg tablets contain the inactive ingredients hypromellose 2208, colloidal silicon dioxide, D&C yellow #10 aluminum lake, and magnesium stearate.
System Components and Performance
Metformin hydrochloride extended-release tablets comprise a monohydrophilic polymer matrix system in which metformin hydrochloride is combined with a drug release controlling polymer to form the matrix. After administration, fluid from the gastrointestinal (GI) tract enters the tablet, causing the polymers to hydrate and swell. Drug is released slowly from the dosage form by a process of diffusion through the gel matrix that is essentially independent of pH. The hydrated polymer system is not rigid and is expected to be broken up by normal peristalsis in the GI tract. The biologically inert components of the tablet may occasionally remain intact during GI transit and will be eliminated in the feces as a soft, hydrated mass.
Clinical Pharmacology
Mechanism of Action
Metformin is an antihyperglycemic agent which improves glucose tolerance in patients with type 2 diabetes, lowering both basal and postprandial plasma glucose. Its pharmacologic mechanisms of action are different from other classes of oral antihyperglycemic agents. Metformin decreases hepatic glucose production, decreases intestinal absorption of glucose and improves insulin sensitivity by increasing peripheral glucose uptake and utilization. Unlike sulfonylureas, metformin does not produce hypoglycemia in either patients with type 2 diabetes or normal subjects (except in special circumstances, see
PRECAUTIONS
) and does not cause hyperinsulinemia. With metformin therapy, insulin secretion remains unchanged while fasting insulin levels and day-long plasma insulin response may actually decrease.
Pharmacokinetics
Absorption and Bioavailability
The absolute bioavailability of a metformin hydrochloride 500 mg tablet given under fasting conditions is approximately 50-60%. Studies using single oral doses of metformin hydrochloride tablets of 500 mg to 1500 mg, and 850 mg to 2550 mg, indicate that there is a lack of dose proportionality with increasing doses, which is due to decreased absorption rather than an alteration in elimination. Food decreases the extent and slightly delays the absorption of metformin, as shown by approximately a 40% lower mean peak plasma concentration (Cmax), a 25% lower area under the plasma concentration versus time curve (AUC), and a 35 minute prolongation of time to peak plasma concentration (Tmax) following administration of a single 850 mg tablet of metformin with food, compared to the same tablet strength administered fasting. The clinical relevance of these decreases is unknown. Following a single oral dose of metformin hydrochloride extended-release tablets, Cmax is achieved with a median value of 7 hours and a range of 4 hours to 8 hours. Peak plasma levels are approximately 20% lower compared to the same dose of metformin hydrochloride tablets, however, the extent of absorption (as measured by AUC) is similar to metformin hydrochloride tablets. At steady state, the AUC and Cmax are less than dose proportional for metformin hydrochloride extended-release tablets within the range of 500 mg to 2000 mg administered once daily. Peak plasma levels are approximately 0.6, 1.1, 1.4, and 1.8for 500, 1000, 1500, and 2000 mg once-daily doses, respectively. The extent of metformin absorption (as measured by AUC) from metformin hydrochloride extended-release tablets at a 2000 mg once-daily dose is similar to the same total daily dose administered as metformin hydrochloride tablets 1000 mg twice daily. After repeated administration of metformin hydrochloride extended-release, metformin did not accumulate in plasma. Within-subject variability in Cmax and AUC of metformin from metformin hydrochloride extended-release tablets is comparable to that with metformin hydrochloride tablets. Although the extent of metformin absorption (as measured by AUC) from the metformin hydrochloride extended-release tablet increased by approximately 50% when given with food, there was no effect of food on Cmax and Tmax of metformin. Both high and low fat meals had the same effect on the pharmacokinetics of metformin hydrochloride extended-release tablets.
Distribution
The apparent volume of distribution (V/F) of metformin following single oral doses of metformin hydrochloride 850 mg tablets averaged 654358 L. Metformin is negligibly bound to plasma proteins in contrast to sulfonylureas, which are more than 90% protein bound. Metformin partitions into erythrocytes, most likely as a function of time. At usual clinical doses and dosing schedules of metformin hydrochloride, steady state plasma concentrations of metformin are reached within 24-48 hours and are generally <1 During controlled clinical trials of metformin hydrochloride tablets, maximum metformin plasma levels did not exceed 5even at maximum doses.
Metabolism and Elimination
Intravenous single-dose studies in normal subjects demonstrate that metformin is excreted unchanged in the urine and does not undergo hepatic metabolism (no metabolites have been identified in humans) nor biliary excretion. Renal clearance (see
Table 1
) is approximately 3.5 times greater than creatinine clearance, which indicates that tubular secretion is the major route of metformin elimination. Following oral administration, approximately 90% of the absorbed drug is eliminated via the renal route within the first 24 hours, with a plasma elimination half-life of approximately 6.2 hours. In blood, the elimination half-life is approximately 17.6 hours, suggesting that the erythrocyte mass may be a compartment of distribution.
Use In Specific Populations
Patients with Type 2 Diabetes
In the presence of normal renal function, there are no differences between single- or multiple-dose pharmacokinetics of metformin between patients with type 2 diabetes and normal subjects (see
Table 1
), nor is there any accumulation of metformin in either group at usual clinical doses. The pharmacokinetics of metformin hydrochloride extended-release tablets in patients with type 2 diabetes are comparable to those in healthy normal adults.
Renal Insufficiency
In patients with decreased renal function (based on measured creatinine clearance), the plasma and blood half-life of metformin is prolonged and the renal clearance is decreased in proportion to the decrease in creatinine clearance (see
Table 1 WARNINGS). Hepatic Insufficiency No pharmacokinetic studies of metformin have been conducted in patients with hepatic insufficiency. Geriatrics Limited data from controlled pharmacokinetic studies of metformin hydrochloride in healthy elderly subjects suggest that total plasma clearance of metformin is decreased, the half-life is prolonged, and Cmax is increased, compared to healthy young subjects. From these data, it appears that the change in metformin pharmacokinetics with aging is primarily accounted for by a change in renal function (see Table 1). Metformin hydrochloride and metformin hydrochloride extended-release treatment should not be initiated in patients80 years of age unless measurement of creatinine clearance demonstrates that renal function is not reduced. (See WARNINGSand DOSAGE AND ADMINISTRATION.) Table 1. Select Mean (Metformin Pharmacokinetic Parameters Following Single or Multiple Oral Doses of Metformin a -All doses given fasting except the first 18 doses of the multiple dose studiesb -Peak plasma concentrationc -Time to peak plasma concentrationd -Combined results (average means) of five studies: mean age 32 years (range 23-59 years)e -Kinetic study done following dose 19, given fastingf -Elderly subjects, mean age 71 years (range 65-81 years)g -CLcr = creatinine clearance normalized to body surface area of 1.73 m2Subject Groups: Metformin dose(number of subjects)Cmaxb (Tmaxc (hrs)Renal Clearance (mL/min)Healthy, nondiabetic adults:500 mg single dose (24)1.03 (2.75 (600 (850 mg single dose (74)d1.60 (2.64 (552 (850 mg three times daily for 19 dosese (9)2.01 (1.79 (642 (Adults with type 2 diabetes:850 mg single dose (23)1.48 (3.32 (491 (850 mg three times daily for 19 dosese (9)1.90 (2.01 (550 (Elderlyf, healthy nondiabetic adults:850 mg single dose (12)2.45 (2.71 (412 (98)Renal-impaired adults:850 mg single doseMild (CLcrg 61-90 mL/min) (5)1.86 (3.20 (384 (Moderate (CLcr 31-60 mL/min) (4)4.12 (3.75 (108 (57)Severe (CLcr 10-30 mL/min) (6)3.93 (4.01 (130 (90) Pediatrics After administration of a single oral metformin hydrochloride 500 mg tablet with food, geometric mean metformin Cmax and AUC differed less than 5% between pediatric type 2 diabetic patients (12 to 16 years of age) and gender- and weight-matched healthy adults (20 to 45 years of age), all with normal renal function. Gender Metformin pharmacokinetic parameters did not differ significantly between normal subjects and patients with type 2 diabetes when analyzed according to gender (males = 19, females = 16). Similarly, in controlled clinical studies in patients with type 2 diabetes, the antihyperglycemic effect of metformin hydrochloride tablets was comparable in males and females. Race No studies of metformin pharmacokinetic parameters according to race have been performed. In controlled clinical studies of metformin hydrochloride tablets in patients with type 2 diabetes, the antihyperglycemic effect was comparable in whites (n = 249), blacks (n = 51) and Hispanics (n = 24).
Clinical Studies
METFORMIN HYDROCHLORIDE TABLETS
In a double-blind, placebo-controlled, multicenter U.S. clinical trial involving obese patients with type 2 diabetes whose hyperglycemia was not adequately controlled with dietary management alone (baseline fasting plasma glucose [FPG] of approximately 240 mg/dL), treatment with metformin hydrochloride tablets (up to 2550 mg/day) for 29 weeks resulted in significant mean net reductions in fasting and postprandial plasma glucose (PPG) and hemoglobin A1c (HbA1c) of 59 mg/dL, 83 mg/dL, and 1.8%, respectively, compared to the placebo group (see
Table 2
). Table 2. Metformin Hydrochloride vs. Placebo Summary of Mean Changes from Baseline* in Plasma Glucose HbA1c and Body Weight, at Final Visit (29-week study) * All patients on diet therapy at Baseline** Not statistically significantMetformin Hydrochloride (n =141)Placebo (n=145)P-ValueFPG (mg/dL)Baseline241.5237.7NS**Change at FINAL VISIT-53.06.30.001Hemoglobin A1c(%)Baseline8.48.2NS**Change at FINAL VISIT-1.40.40.001Body Weight (lbs)Baseline201.0206.0NS**Change at FINAL VISIT-1.4-2.4NS**A 29-week, double-blind, placebo-controlled study of metformin hydrochloride tablets and glyburide, alone and in combination, was conducted in obese patients with type 2 diabetes who had failed to achieve adequate glycemic control while on maximum doses of glyburide (baseline FPG of approximately 250 mg/dL) (see
Table 3
). Patients randomized to the combination arm started therapy with metformin hydrochloride tablets 500 mg and glyburide 20 mg. At the end of each week of the first four weeks of the trial, these patients had their dosages of metformin hydrochloride tablets increased by 500 mg if they had failed to reach target fasting plasma glucose. After week four, such dosage adjustments were made monthly, although no patient was allowed to exceed metformin hydrochloride tablets 2500 mg. Patients in the metformin hydrochloride tablets only arm (metformin plus placebo) followed the same titration schedule. At the end of the trial, approximately 70% of the patients in the combination group were taking metformin hydrochloride tablets 2000 mg/glyburide 20 mg or metformin hydrochloride tablets 2500 mg/glyburide 20 mg. Patients randomized to continue on glyburide experienced worseningof glycemic control, with mean increases in FPG, PPG and HbA1c of 14 mg/dL, 3 mg/dL and 0.2%, respectively. In contrast, those randomized to metformin hydrochloride tablets (up to 2500 mg/day) experienced a slight improvement, with mean reductions in FPG, PPG and HbA1c of 1 mg/dL, 6 mg/dL and 0.4%, respectively. The combination of metformin hydrochloride tablets and glyburide was effective in reducing FPG, PPG and HbA1c levels by 63 mg/dL, 65 mg/dL, and 1.7%, respectively. Compared to results of glyburide treatment alone, the net differences with combination treatment were -77 mg/dL, -68 mg/dL and -1.9%, respectively (see
Table 3
). Table 3. Combined Metformin/Glyburide (Comb) vs. Glyburide (Glyb) or Metformin Hydrochloride (MET) Monotherapy: Summary of Mean Changes from Baseline* in Fasting Plasma Flucose, HbA1c and Body Weight, at Final Visit (29-week study) *All patients on glyburide, 20 mg/day, at Baseline**Not statically significantComb (n=213)Glyb (n=209)MET (n=210)p-valuesGlyb vs. CombMET vs. CombMET vs. GlybFasting PlasmaGlucose (mg/dL)Baseline250.5247.5253.9NS**NS**NS**Change at FINAL VISIT-63.513.7-0.90.0010.0010.025Hemoglobin A1c(%)Baseline8.88.58.9NS**NS**0.007Change at FINAL VISIT-1.70.2-0.40.0010.0010.001Body Weight (lbs.)Baseline202.2203.0204.0NS**NS**NS**Change at FINAL VISIT0.9-0.7-8.40.0110.0010.001The magnitude of the decline in fasting blood glucose concentration following the institution of metformin hydrochloride tablets therapy was proportional to the level of fasting hyperglycemia. Patients with type 2 diabetes with higher fasting glucose concentrations experienced greater declines in plasma glucose and glycosylated hemoglobin. In clinical studies, metformin hydrochloride tablets, alone or in combination with a sulfonylurea, lowered mean fasting serum triglycerides, total cholesterol and LDL cholesterol levels and had no adverse effects on other lipid levels (see
Table 4
). Table 4. Summary of Mean Percent Change from Baseline of Major Serum Lipid Variables at Final Visit (29-week studies) Metformin Hydrochloride vs. PlaceboCombined Metformin/ Glyburide vs. MonotherapyMetformin Hydrochloride (n=141)Placebo (n=145)Metformin Hydrochloride (n=141)Metformin Hydrochloride/ Glyburide (n=213)Glyburide (n=209)Total Cholesterol (mg/dL)Baseline211.0212.3213.1215.6219.6Mean %change atFINAL VISIT-5%1%-2%-4%1%Total Triglycerides (mg/dL)Baseline236.1203.5242.5215.0266.1Mean %change atFINAL VISIT-16%1%-3%-8%4%LDL-Cholesterol (mg/dL)Baseline135.4138.5134.3136.0137.5Mean %change atFINAL VISIT-8%1%-4%-6%3%HDL-Cholesterol (mg/dL)Baseline39.040.537.239.037.0Mean %change atFINAL VISIT2%-1%5%3%1%In contrast to sulfonylureas, body weight of individuals on metformin hydrochloride tablets tended to remain stable or even decrease somewhat (see
Tables 2
and
3
). A 24-week, double-blind, placebo-controlled study of metformin hydrochloride tablets plus insulin versus insulin plus placebo was conducted in patients with type 2 diabetes who failed to achieve adequate glycemic control on insulin alone (see
Table 5
). Patients randomized to received metformin hydrochloride tablets plus insulin achieved a reduction in HbA1c of 2.10%, compared to 1.56% reduction in HbA1c achieved by insulin plus placebo. The improvement in glycemic control was achieved at the final study visit with 16% less insulin, 93.0 U/day vs. 110.6 U/day, metformin hydrochloride tablets plus insulin versus insulin plus placebo, respectively p. 0.04. Table 5. Combined Metformin Hydrochloride/Insulin vs. Placebo/Insulin Summary of Mean Changes from Baseline in HbA1c and Daily Insulin Dose significant using analysis of covariance with baseline as covariate (p=0.04)Not significant using analysis of variance (values shown in table)b Statistically significant for insulin (p=0.04)Metformin Hydrochloride/Insulin (n=26)Placebo/Insulin (n=28)Treatment difference MeanSEHemoglobin A1c(%)Baseline8.959.32Change at FINAL VISIT-2.10-1.56-0.540.43Insulin Dose (U/day)Baseline93.1294.64Change at FINAL VISIT-0.1515.6316.087.77bA second double-blind, placebo-controlled study (n=51), with 16 weeks of randomized treatment, demonstrated that in patients with type 2 diabetes controlled on insulin for 8 weeks with an average of HbA1c of 7.460.97%, the addition of metformin hydrochloride tablets maintained similar glycemic control (HbA1c 7.150.61 versus 6.970.62 for metformin hydrochloride tablets plus insulin and placebo plus insulin respectively) with 19% less insulin versus baseline (reduction of 23.6830.22 versus an increase of 0.4325.20 units for metformin hydrochloride tablets plus insulin and placebo plus insulin, p<0.01). In addition, this study demonstrated that the combination of metformin hydrochloride tablets plus insulin resulted in reduction in body weight of 3.114.30 lbs, compared to an increase of 1.306.08 lbs for placebo plus insulin, p=0.01.
METFORMIN HYDROCHLORIDE EXTENDED-RELEASE TABLETS
A 24-week, double-blind, placebo-controlled study of metformin hydrochloride extended-release tablets, taken once daily with the evening meal, was conducted in patients with type 2 diabetes who had failed to achieve glycemic control with diet and exercise (HbA1c 7.0-10.0%, FPG 126-270 mg/dL). Patients entering the study had a mean baseline HbA1c of 8.0% and a mean baseline FPG of 176 mg/dL. After 12 weeks treatment, mean HbA1c had increased from baseline by 0.1% and mean FPG decreased from baseline by 2 mg/dL in the placebo group, compared with a decrease in mean HbA1c of 0.6% and a decrease in mean FPG of 23 mg/dL in patients treated with metformin hydrochloride extended-release tablets 1000 mg once daily. Subsequently, the treatment dose was increased to 1500 mg once daily if HbA1c was7.0 % but <8.0% (patients with HbA1c8.0% were discontinued from the study). At the final visit (24- week), mean HbA1c had increased 0.2% from baseline in placebo patients and decreased 0.6% with metformin hydrochloride extended-release tablets. A 16-week, double-blind, placebo-controlled, dose-response study of metformin hydrochloride extended-release tablets, taken once daily with the evening meal, or twice daily with meals, was conducted in patients with type 2 diabetes who had failed to achieve glycemic control with diet and exercise (HbA1c 7.0-11%, FPG 126-280 mg/dL). Changes in glycemic control and body weight are shown in
Table 6
. Table 6. Summary of Mean Changes from Baseline* in HbA1c, Fasting Plasma Glucose, and Body Weight at Final Visit (16-week study) * All patients on diet therapy at BaselineAll comparisons versus Placebo** Not statistically significantMetformin hydrochloride extended-release500 mg Once Daily1000 mg Once Daily1500 mg Once Daily2000 mg Once Daily1000 mg Twice DailyPlaceboHemoglobin A1c(%)(n=115)(n=115)(n=111)(n=125)(n=112)(n=111)Baseline8.28.48.38.48.48.4Change at FINAL VISIT-0.4-0.6-0.9-0.8-1.10.1p-value<0.001<0.001<0.001<0.001<0.001-FPG (mg/dL)(n=126)(n=118)(n=120)(n=132)(n=122)(n=113)Baseline182.7183.7178.9181.0181.6179.6Change at FINAL VISIT-15.2-19.3-28.5-29.9-33.67.6p-value<0.001<0.001<0.001<0.001<0.001-Body Weight (lbs)(n=125)(n=119)(n=117)(n=131)(n=119)(n=113)Baseline192.9191.8188.3195.4192.5194.3Change at FINAL VISIT-1.3-1.3-0.7-1.5-2.2-1.8p-valueNS**NS**NS**NS**NS**-Compared with placebo, improvement in glycemic control was seen at all dose levels of metformin hydrochloride extended-release tablets and treatment was not associated with any significant change in weight (see
DOSAGE AND ADMINISTRATION
for dosing recommendations for metformin hydrochloride tablets and metformin hydrochloride extended-release tablets). A 24-week, double-blind, randomized study of metformin hydrochloride extended-release tablets, taken once daily with the evening meal, and metformin hydrochloride tablets, taken twice daily (with breakfast and evening meal), was conducted in patients with type 2 diabetes who had been treated with metformin hydrochloride tablets 500 mg twice daily for at least 8 weeks prior to study entry. The metformin hydrochloride tablets dose had not necessarily been titrated to achieve a specific level of glycemic control prior to study entry. Patients qualified for the study if HbA1c was8.5 % and FPG was200 mg/dL. Changes in glycemic control and body weight are shown in
Table 7
. Table 7. Summary of Mean Changes from Baseline* in HbA1c, Fasting Plasma Glucose, and Body Weight at Week 12 and at Final Visit (24-week study) *All patients on metformin hydrochloride tablets 500 mg twice daily at Baselinen=68MetforminMetformin Hydrochloride Extended-release TabletsHydrochloride Tablets 500 mg Twice Daily1000 mg Once Daily1500 mg Once DailyHemoglobin A1c(%)(n=67)(n=72)(n=66)Baseline7.066.997.02Change at 12 Weeks0.140.230.04(95% CI)(-0.03, 0.31)(0.10, 0.36)(-0.08, 0.15)Change at FINAL VISIT0.140.270.13(95%)(-0.04, 0.31)(0.11, 0.43)(-0.02, 0.28)FPG (mg/dL)(n=69)(n=72)(n=70)Baseline127.2131.0131.4Change at 12 Weeks12.99.53.7(95% CI)(6.5, 19.4)(4.4, 14.6)(-0.4, 7.8)Change at FINAL VISIT14.011.57.6(95%)(7.0, 21.0)(4.4, 18.6)(1.0, 14.2)Body Weight (lbs)(n=71)(n=74)(n=71)Baseline210.3202.8192.7Change at 12 Weeks0.40.90.7(95% CI)(-0.04, 1.5)(0.0, 2.0)(-0.04, 1.8)Change at FINAL VISIT0.91.10.9(95%)(-0.04, 2.2)(-0.2, 2.4)(-0.4, 2.0)
DOSAGE AND ADMINISTRATION
). Changes in lipid parameters in the previously described placebo-controlled dose-response study of metformin hydrochloride extended-release tablets are shown in
Table 8
. Table 8. Summary of Mean Percent Changes from Baseline* in Major Lipid Variables at Final Visit (16-week study) *All patients on diet therapy at BaselineMetformin Hydrochloride Extended-release Tablets500 mg Once Daily1000 mg Once Daily1500 mg Once Daily2000 mg Once Daily1000 mg Twice DailyPlaceboTotal Cholesterol(mg/dL)(n=120)(n=113)(n=110)(n=126)(n=117)(n=110)Baseline210.3218.1214.6204.4208.2208.6Mean % change atFINAL VISIT1.0%1.7%0.7%-1.6%-2.6%2.6%Total Triglycerides(mg/dL)(n=120)(n=113)(n=110)(n=126)(n=117)(n=110)Baseline220.2211.9198.8194.2179.0211.7Mean % change atFINAL VISIT14.5%9.4%15.1%14.9%9.4%10.9%LDL-Cholesterol(mg/dL)(n=119)(n=113)(n=109)(n=126)(n=117)(n=107)Baseline131.0134.9135.8125.8131.4131.9Mean % change atFINAL VISIT-1.4%-1.6%-3.5%-3.3%-5.5%3.2%HDL-Cholesterol(mg/dL)(n=120)(n=108)(n=108)(n=125)(n=117)(n=108)Baseline40.841.640.640.242.439.4Mean % change atFINAL VISIT6.2%8.6%5.5%6.1%7.1%5.8%Changes in lipid parameters in the previously described study of metformin hydrochloride tablets and metformin hydrochloride extended-release tablets are shown in
Table 9
. Table 9. Summary of Mean Percent Changes from Baseline* in Major Lipid Variables at Final Visit (24-week study) *All patients on metformin hydrochloride tablets 500 mg twice daily at BaselineMetformin Hydrochloride TabletsMetformin Hydrochloride Extended-release Tablets500 mg Twice Daily1000 mg Once Daily1500 mg Once DailyTotal Cholesterol (mg/dL)(n=68)(n=70)(n=66)Baseline199.0201.9201.6Mean % change at FINAL VISIT0.1%1.3%0.1%Total Triglycerides (mg/dL)(n=68)(n=70)(n=66)Baseline178.0169.2206.8Mean % change at FINAL VISIT6.3%25.3%33.4%LDL-Cholesterol (mg/dL)(n=68)(n=70)(n=66)Baseline122.1126.2115.7Mean % change at FINAL VISIT-1.3%-3.3%-3.7%HDL-Cholesterol (mg/dL)(n=68)(n=70)(n=65)Baseline41.941.744.6Mean % change at FINAL VISIT4.8%1.0%-2.1%
Pediatric Clinical Studies
In a double-blind, placebo-controlled study in pediatric patients aged 10 to 16 years with type 2 diabetes (mean FPG 182.2 mg/dL), treatment with metformin hydrochloride tablets (up to 2000 mg/day) for up to 16 weeks (mean duration of treatment 11 weeks) resulted in a significant mean net reduction in FPG of 64.3 mg/dL, compared with placebo (see
Table 10
). Table 10. Metformin Hydrochloride Tablets vs. Placebo (PediatricsSummary of Mean Changes from Baseline* in Plasma Glucose and Body Weight at Final Visit Pediatric patients mean age 13.8 years (range 10-16 years)* All patients on diet therapy at Baseline** Not statistically significantMetformin Hydrochloride TabletsPlacebop-ValueFPG (mg/dL)(n=37)(n=36)Baseline162.4192.3Change at FINAL VISIT-42.921.4<0.001Body Weight (lbs)(n=39)(n=38)Baseline205.3189.4Change at FINAL VISIT-3.3-2.0NS**
Indications & Usage
Metformin hydrochloride tablets and metformin hydrochloride extended-release tablets, as monotherapy, are indicated as an adjunct to diet and exercise to improve glycemic control in patients with type 2 diabetes. Metformin hydrochloride tablets are indicated in patients 10 years of age and older, and metformin hydrochloride extended-release tablets are indicated in patients 17 years of age and older. Metformin hydrochloride tablets or metformin hydrochloride extended-release tablets may be used concomitantly with a sulfonylurea or insulin to improve glycemic control in adults (17 years of age and older).
Contraindications
Metformin hydrochloride tablets and metformin hydrochloride extended-release tablets are contraindicated in patients with: 1. Renal disease or renal dysfunction (e.g., as suggested by serum creatinine levels1.5 mg/dL [males],1.4 mg/dL [females] or abnormal creatinine clearance) which may also result from conditions such as cardiovascular collapse (shock), acute myocardial infarction, and septicemia (see
WARNINGS
and
PRECAUTIONS
). 2. Known hypersensitivity to metformin hydrochloride. 3. Acute or chronic metabolic acidosis, including diabetic ketoacidosis, with or without coma. Diabetic ketoacidosis should be treated with insulin. Metformin hydrochloride tablets and metformin hydrochloride extended-release tablets should be temporarily discontinued in patients undergoing radiologic studies involving intravascular administration of iodinated contrast materials, because use of such products may result in acute alteration of renal function. (See also
PRECAUTIONS
).
Warnings
Lactic Acidosis: are generally found. The reported incidence of lactic acidosis in patients receiving metformin hydrochloride is very low (approximately 0.03 cases/1000 patient-years, with approximately 0.015 fatal cases/1000 patient-years). In more than 20,000 patient-years exposure to metformin in clinical trials, there were no reports of lactic acidosis. Reported cases have occurred primarily in diabetic patients with significant renal insufficiency, including both intrinsic renal disease and renal hypoperfusion, often in the setting of multiple concomitant medical/surgical problems and multiple concomitant medications. Patients with congestive heart failure requiring pharmacologic management, in particular those with unstable or acute congestive heart failure who are at risk of hypoperfusion and hypoxemia, are at increased risk of lactic acidosis. The risk of lactic acidosis increases with the degree of renal dysfunction and the patient's age. The risk of lactic acidosis may, therefore, be significantly decreased by regular monitoring of renal function in patients taking metformin hydrochloride tablets or metformin hydrochloride extended-release tablets and by use of the minimum effective dose of metformin hydrochloride tablets or metformin hydrochloride extended-release tablets. In particular, treatment of the elderly should be accompanied by careful monitoring of renal function. Metformin hydrochloride tablets or metformin hydrochloride extended-release tablets treatment should not be initiated in patients80 years of age unless measurement of creatinine clearance demonstrates that renal function is not reduced, as these patients are more susceptible to developing lactic acidosis. In addition, metformin hydrochloride tablets and metformin hydrochloride extended-release tablets should be promptly withheld in the presence of any condition associated with hypoxemia, dehydration, or sepsis. Because impaired hepatic function may significantly limit the ability to clear lactate, metformin hydrochloride tablets and metformin hydrochloride extended-release tablets should generally be avoided in patients with clinical or laboratory evidence of hepatic disease. Patients should be cautioned against excessive alcohol intake, either acute or chronic, when taking metformin hydrochloride tablets or metformin hydrochloride extended-release tablets, since alcohol potentiates the effects of metformin hydrochloride on lactate metabolism. In addition, metformin hydrochloride tablets and metformin hydrochloride extended-release tablets should be temporarily discontinued prior to any intravascular radiocontrast study and for any surgical procedure (see alsoPRECAUTIONS). The onset of lactic acidosis often is subtle, and accompanied only by nonspecific symptoms such as malaise, myalgias, respiratory distress, increasing somnolence, and nonspecific abdominal distress. There may be associated hypothermia, hypotension, and resistant bradyarrhythmias with more marked acidosis. The patient and the patient's physician must be aware of the possible importance of such symptoms and the patient should be instructed to notify the physician immediately if they occur (see alsoPRECAUTIONS). Metformin hydrochloride tablets and metformin hydrochloride extended-release tablets should be withdrawn until the situation is clarified. Serum electrolytes, ketones, blood glucose and, if indicated, blood pH, lactate levels, and even blood metformin levels may be useful. Once a patient is stabilized on any dose level of metformin hydrochloride tablets or metformin hydrochloride extended-release tablets, gastrointestinal symptoms, which are common during initiation of therapy, are unlikely to be drug related. Later occurrence of gastrointestinal symptoms could be due to lactic acidosis or other serious disease. Levels of fasting venous plasma lactate above the upper limit of normal but less than 5 mmol/L in patients taking metformin hydrochloride tablets or metformin hydrochloride extended-release tablets do not necessarily indicate impending lactic acidosis and may be explainable by other mechanisms, such as poorly controlled diabetes or obesity, vigorous physical activity, or technical problems in sample handling. (See alsoPRECAUTIONS.) Lactic acidosis should be suspected in any diabetic patient with metabolic acidosis lacking evidence of ketoacidosis (ketonuria and ketonemia). Lactic acidosis is a medical emergency that must be treated in a hospital setting. In a patient with lactic acidosis who is taking metformin hydrochloride tablets or metformin hydrochloride extended-release tablets, the drug should be discontinued immediately and general supportive measures promptly instituted. Because metformin hydrochloride is dialyzable (with a clearance of up to 170 mL/min under good hemodynamic conditions), prompt hemodialysis is recommended to correct the acidosis and remove the accumulated metformin. Such management often results in prompt reversal of symptoms and recovery. (See alsoCONTRAINDICATIONSandPRECAUTIONS.)
Precautions
General
Monitoring of renal functionMetformin is known to be substantially excreted by the kidney, and the risk of metformin accumulation and lactic acidosis increases with the degree of impairment of renal function. Thus, patients with serum creatinine levels above the upper limit of normal for their age should not receive metformin hydrochloride tablets or metformin hydrochloride extended-release tablets. In patients with advanced age, metformin hydrochloride tablets and metformin hydrochloride extended-release tablets should be carefully titrated to establish the minimum dose for adequate glycemic effect, because aging is associated with reduced renal function. In elderly patients, particularly those80 years of age, renal function should be monitored regularly and, generally, metformin hydrochloride tablets and metformin hydrochloride extended-release tablets should not be titrated to the maximum dose (see
WARNINGS
and
DOSAGE AND ADMINISTRATION
). Before initiation of metformin hydrochloride tablets or metformin hydrochloride extended-release tablets therapy and at least annually thereafter, renal function should be assessed and verified as normal. In patients in whom development of renal dysfunction is anticipated, renal function should be assessed more frequently and metformin hydrochloride tablets or metformin hydrochloride extended-release tablets discontinued if evidence of renal impairment is present. Use of concomitant medications that may affect renal function or metformin dispositionConcomitant medication(s) that may affect renal function or result in significant hemodynamic change or may interfere with the disposition of metformin, such as cationic drugs that are eliminated by renal tubular secretion (See
PRECAUTIONS: Drug Interactions
), should be used with caution. Radiologic studies involving the use of intravascular iodinated contrast materials (for example, intravenous urogram, intravenous cholangiography, angiography, and computed tomography (CT) scans with contrast materials)Intravascular contrast studies with iodinated materials can lead to acute alteration of renal function and have been associated with lactic acidosis in patients receiving metformin (see
CONTRAINDICATIONS
). Therefore, in patients in whom any such study is planned, metformin hydrochloride tablets or metformin hydrochloride extended-release tablets should be temporarily discontinued at the time of or prior to the procedure, and withheld for 48 hours subsequent to the procedure and reinstituted only after renal function has been re-evaluated and found to be normal. Hypoxic statesCardiovascular collapse (shock) from whatever cause, acute congestive heart failure, acute myocardial infarction and other conditions characterized by hypoxemia have been associated with lactic acidosis and may also cause prerenal azotemia. When such events occur in patients on metformin hydrochloride tablets or metformin hydrochloride extended-release tablets therapy, the drug should be promptly discontinued. Surgical proceduresMetformin hydrochloride tablets or metformin hydrochloride extended-release tablets therapy should be temporarily suspended for any surgical procedure (except minor procedures not associated with restricted intake of food and fluids) and should not be restarted until the patient's oral intake has resumed and renal function has been evaluated as normal. Alcohol intakeAlcohol is known to potentiate the effect of metformin on lactate metabolism. Patients, therefore, should be warned against excessive alcohol intake, acute or chronic, while receiving metformin hydrochloride tablets or metformin hydrochloride extended-release tablets. Impaired hepatic functionSince impaired hepatic function has been associated with some cases of lactic acidosis, metformin hydrochloride tablets and metformin hydrochloride extended-release tablets should generally be avoided in patients with clinical or laboratory evidence of hepatic disease. Vitamin B12levelsIn controlled clinical trials of metformin hydrochloride tablets of 29 weeks duration, a decrease to subnormal levels of previously normal serum Vitamin B12 levels, without clinical manifestations, is observed in approximately 7% of patients. Such decrease, possibly due to interference with B12 absorption from the B12 -intrinsic factor complex, is, however, very rarely associated with anemia and appears to be rapidly reversible with discontinuation of metformin hydrochloride tablets or Vitamin B12 supplementation. Measurement of hematologic parameters on an annual basis is advised in patients on metformin hydrochloride tablets or metformin hydrochloride extendedrelease tablets and any apparent abnormalities should be appropriately investigated and managed (see
PRECAUTIONS: Laboratory Tests
) Certain individuals (those with inadequate Vitamin B12 or calcium intake or absorption) appear to be predisposed to developing subnormal Vitamin B12 levels. In these patients, routine serum Vitamin B12 measurements at two- to three-years intervals may be useful. Change in clinical status of patients with previously controlled type 2 diabetesA patient with type 2 diabetes previously well controlled on metformin hydrochloride tablets or metformin hydrochloride extended-release tablets who develops laboratory abnormalities or clinical illness (especially vague and poorly defined illness) should be evaluated promptly for evidence of ketoacidosis or lactic acidosis. Evaluation should include serum electrolytes and ketones, blood glucose and, if indicated, blood pH, lactate, pyruvate, and metformin levels. If acidosis of either form occurs, metformin hydrochloride tablets or metformin hydrochloride extended-release tablets must be stopped immediately and other appropriate corrective measures initiated (see also
WARNINGS
). HypoglycemiaHypoglycemia does not occur in patients receiving metformin hydrochloride tablets or metformin hydrochloride extended-release tablets alone under usual circumstances of use, but could occur when caloric intake is deficient, when strenuous exercise is not compensated by caloric supplementation, or during concomitant use with other glucose-lowering agents (such as sulfonylureas and insulin) or ethanol. Elderly, debilitated, or malnourished patients, and those with adrenal or pituitary insufficiency or alcohol intoxication are particularly susceptible to hypoglycemic effects. Hypoglycemia may be difficult to recognize in the elderly, and in people who are taking beta-adrenergic blocking drugs. Loss of control of blood glucoseWhen a patient stabilized on any diabetic regimen is exposed to stress such as fever, trauma, infection, or surgery, a temporary loss of glycemic control may occur. At such times, it may be necessary to withhold metformin hydrochloride tablets or metformin hydrochloride extended-release tablets and temporarily administer insulin. Metformin hydrochloride tablets or metformin hydrochloride extended-release tablets may be reinstituted after the acute episode is resolved. The effectiveness of oral antidiabetic drugs in lowering blood glucose to a targeted level decreases in many patients over a period of time. This phenomenon, which may be due to progression of the underlying disease or to diminished responsiveness to the drug, is known as secondary failure, to distinguish it from primary failure in which the drug is ineffective during initial therapy. Should secondary failure occur with either metformin hydrochloride tablets or metformin hydrochloride extended-release tablets or sulfonylurea monotherapy, combined therapy with metformin hydrochloride tablets or metformin hydrochloride extended-release tablets and sulfonylurea may result in a response. Should secondary failure occur with combined metformin hydrochloride tablets/sulfonylurea therapy or metformin hydrochloride extended-release tablets/sulfonylurea therapy, it may be necessary to consider therapeutic alternatives including initiation of insulin therapy.
Information For Patients
Patients should be informed of the potential risks and benefits of metformin hydrochloride tablets or metformin hydrochloride extended-release tablets and of alternative modes of therapy. They should also be informed about the importance of adherence to dietary instructions, of a regular exercise program, and of regular testing of blood glucose, glycosylated hemoglobin, renal function and hematologic parameters. The risks of lactic acidosis, its symptoms, and conditions that predispose to its development, as noted in the
WARNINGS
and
PRECAUTIONS
sections, should be explained to patients. Patients should be advised to discontinue metformin hydrochloride tablets or metformin hydrochloride extended-release tablets immediately and to promptly notify their health practitioner if unexplained hyperventilation, myalgia, malaise, unusual somnolence or other nonspecific symptoms occur. Once a patient is stabilized on any dose level of metformin hydrochloride tablets or metformin hydrochloride extended-release tablets, gastrointestinal symptoms, which are common during initiation of metformin therapy, are unlikely to be drug related. Later occurrence of gastrointestinal symptoms could be due to lactic acidosis or other serious disease. Patients should be counseled against excessive alcohol intake, either acute or chronic, while receiving metformin hydrochloride tablets or metformin hydrochloride extended-release tablets. Metformin hydrochloride tablets or metformin hydrochloride extended-release tablets alone does not usually cause hypoglycemia, although it may occur when metformin hydrochloride tablets or metformin hydrochloride extended-release tablets are used in conjunction with oral sulfonylureas and insulin. When initiating combination therapy, the risks of hypoglycemia, its symptoms and treatment, and conditions that predispose to its development should be explained to patients. (See Patient Information Printed Separately.) Patients should be informed that metformin hydrochloride extended-release tablets must be swallowed whole and not crushed or chewed, and that the inactive ingredients may occasionally be eliminated in the feces as a soft mass that may resemble the original tablet.
Laboratory Tests
Response to all diabetic therapies should be monitored by periodic measurements of fasting blood glucose and glycosylated hemoglobin levels, with a goal of decreasing these levels toward the normal range. During initial dose titration, fasting glucose can be used to determine the therapeutic response. Thereafter, both glucose and glycosylated hemoglobin should be monitored. Measurements of glycosylated hemoglobin may be especially useful for evaluating long-term control (see also
DOSAGE AND ADMINISTRATION
). Initial and periodic monitoring of hematologic parameters (e.g., hemoglobin/hematocrit and red blood cell indices) and renal function (serum creatinine) should be performed, at least on an annual basis. While megaloblastic anemia has rarely been seen with metformin hydrochloride tablets therapy, if this is suspected, Vitamin B12 deficiency should be excluded.
Drug Interactions
(clinical evaluation of drug interactions done with metformin hydrochloride tablets)
Glyburide: In a single-dose interaction study in type 2 diabetes subjects, co-administration of metformin and glyburide did not result in any changes in either metformin pharmacokinetics or pharmacodynamics. Decreases in glyburide AUC and Cmax were observed, but were highly variable. The single-dose nature of this study and the lack of correlation between glyburide blood levels and pharmacodynamic effects, makes the clinical significance of this interaction uncertain (see
DOSAGE AND ADMINISTRATION:Concomitant Metformin Hydrochloride Tablets or Metformin Hydrochloride Extended-release Tablets and Oral Sulfonylurea Therapy
). Furosemide: A single-dose, metformin-furosemide drug interaction study in healthy subjects demonstrated that pharmacokinetic parameters of both compounds were affected by co-administration. Furosemide increased the metformin plasma and blood Cmax by 22% and blood AUC by 15%, without any significant change in metformin renal clearance. When administered with metformin, the Cmax and AUC of furosemide were 31% and 12% smaller, respectively, than when administered alone, and the terminal half-life was decreased by 32%, without any significant change in furosemide renal clearance. No information is available about the interaction of metformin and furosemide when co-administered chronically. Nifedipine: A single-dose, metformin-nifedipine drug interaction study in normal healthy volunteers demonstrated that co-administration of nifedipine increased plasma metformin Cmax and AUC by 20% and 9%, respectively, and increased the amount excreted in the urine. Tmax and half-life were unaffected. Nifedipine appears to enhance the absorption of metformin. Metformin had minimal effects on nifedipine. Cationic Drugs: Cationic drugs (e.g., amiloride, digoxin, morphine, procainamide, quinidine, quinine, ranitidine, triamterene, trimethoprim, and vancomycin) that are eliminated by renal tubular secretion theoretically have the potential for interaction with metformin by competing for common renal tubular transport systems. Such interaction between metformin and oral cimetidine has been observed in normal healthy volunteers in both single- and multiple-dose, metformin-cimetidine drug interaction studies, with a 60% increase in peak metformin plasma and whole blood concentrations and a 40% increase in plasma and whole blood metformin AUC. There was no change in elimination half-life in the single-dose study. Metformin had no effect on cimetidine pharmacokinetics. Although such interactions remain theoretical (except for cimetidine), careful patient monitoring and dose adjustment of metformin hydrochloride tablets or metformin hydrochloride extended-release tablets and/or the interfering drug is recommended in patients who are taking cationic medications that are excreted via the proximal renal tubular secretory system. Other: Certain drugs tend to produce hyperglycemia and may lead to loss of glycemic control. These drugs include the thiazides and other diuretics, corticosteroids, phenothiazines, thyroid products, estrogens, oral contraceptives, phenytoin, nicotinic acid, sympathomimetics, calcium channel blocking drugs, and isoniazid. When such drugs are administered to a patient receiving metformin hydrochloride tablets or metformin hydrochloride extended-release tablets, the patient should be closely observed for loss of blood glucose control. When such drugs are withdrawn from a patient receiving metformin hydrochloride tablets or metformin hydrochloride extendedrelease tablets, the patient should be observed closely for hypoglycemia. In healthy volunteers, the pharmacokinetics of metformin and propranolol and metformin and ibuprofen were not affected when co-administered in single-dose interaction studies. Metformin is negligibly bound to plasma proteins and is, therefore, less likely to interact with highly protein-bound drugs such as salicylates, sulfonamides, chloramphenicol, and probenecid, as compared to the sulfonylureas, which are extensively bound to serum proteins.
Carcinogenesis & Mutagenesis & Impairment Of Fertility
Long-term carcinogenicity studies have been performed in rats (dosing duration of 104 weeks) and mice (dosing duration of 91 weeks) at doses up to and including 900 mg/kg/day and 1500 mg/kg/day, respectively. These doses are both approximately four times the maximum recommended human daily dose of 2000 mg based on body surface area comparisons. No evidence of carcinogenicity with metformin was found in either male or female mice. Similarly, there was no tumorigenic potential observed with metformin in male rats. There was, however, an increased incidence of benign stromal uterine polyps in female rats treated with 900 mg/kg/day. There was no evidence of mutagenic potential of metformin in the following in vitro tests: Ames test (S. typhimurium), gene mutation test (mouse lymphoma cells), or chromosomal aberrations test (human lymphocytes). Results in the in vivo mouse micronucleus test were also negative. Fertility of male or female rats was unaffected by metformin administration at doses as high as 600 mg/kg/day, which is approximately three times the maximum recommended human daily dose based on body surface area comparisons.
Pregnancy
Teratogenic Effects: Pregnancy Category B.
Recent information strongly suggests that abnormal blood glucose levels during pregnancy are associated with a higher incidence of congenital abnormalities. Most experts recommend that insulin be used during pregnancy to maintain blood glucose levels as close to normal as possible. Because animal reproduction studies are not always predictive of human response, metformin hydrochloride tablets and metformin hydrochloride extended-release tablets should not be used during pregnancy unless clearly needed. There are no adequate and well-controlled studies in pregnant women with metformin hydrochloride tablets or metformin hydrochloride extended-release tablets. Metformin was not teratogenic in rats and rabbits at doses up to 600 mg/kg/day. This represents an exposure of about two and six times the maximum recommended human daily dose of 2000 mg based on body surface area comparisons for rats and rabbits, respectively. Determination of fetal concentrations demonstrated a partial placental barrier to metformin.
Nursing Mothers
Studies in lactating rats show that metformin is excreted into milk and reaches levels comparable to those in plasma. Similar studies have not been conducted in nursing mothers. Because the potential for hypoglycemia in nursing infants may exist, a decision should be made whether to discontinue nursing or to discontinue the drug, taking into account the importance of the drug to the mother. If metformin hydrochloride tablets or metformin hydrochloride extended-release tablets are discontinued, and if diet alone is inadequate for controlling blood glucose, insulin therapy should be considered
Pediatric Use
The safety and effectiveness of metformin hydrochloride tablets for the treatment of type 2 diabetes have been established in pediatric patients ages 10 to 16 years (studies have not been conducted in pediatric patients below the age of 10 years). Use of metformin hydrochloride tablets in this age group is supported by evidence from adequate and well-controlled studies of metformin hydrochloride tablets in adults with additional data from a controlled clinical study in pediatric patients ages 10-16 years with type 2 diabetes, which demonstrated a similar response in glycemic control to that seen in adults. (See
CLINICAL PHARMACOLOGY: Pediatric Clinical Studies.
) In this study, adverse effects were similar to those described in adults. (See
ADVERSE REACTIONS: Pediatric Patients.
) A maximum daily dose of 2000 mg is recommended. (See
DOSAGE AND ADMINISTRATION: Recommended Dosing Schedule: Pediatrics
.) Safety and effectiveness of metformin hydrochloride extended-release tablets in pediatric patients have not been established.
Geriatric Use
Controlled clinical studies of metformin hydrochloride tablets and metformin hydrochloride extended-release tablets did not include sufficient numbers of elderly patients to determine whether they respond differently from younger patients, although other reported clinical experience has not identified differences in responses between the elderly and younger patients. Metformin is known to be substantially excreted by the kidney and because the risk of serious adverse reactions to the drug is greater in patients with impaired renal function, metformin hydrochloride tablets, and metformin hydrochloride extended-release tablets should only be used in patients with normal renal function (see
CONTRAINDICATIONS
,
WARNINGS
and
CLINICAL PHARMACOLOGY: Pharmacokinetics
). Because aging is associated with reduced renal function, metformin hydrochloride tablets or metformin hydrochloride extended-release tablets should be used with caution as age increases. Care should be taken in dose selection and should be based on careful and regular monitoring of renal function. Generally, elderly patients should not be titrated to the maximum dose of metformin hydrochloride tablets or metformin hydrochloride extended-release tablets (see also
WARNINGS
and
DOSAGE AND ADMINISTRATION
).
Adverse Reactions
In a U.S. double-blind clinical study of metformin hydrochloride tablets in patients with type 2 diabetes, a total of 141 patients received metformin hydrochloride tablets therapy (up to 2550 mg per day) and 145 patients received placebo. Adverse reactions reported in greater than 5% of the metformin hydrochloride tablets patients, and that were more common in metformin hydrochloride tablets than placebo-treated patients, are uled in
Table 11
. Table 11. Most Common Adverse Reactions (>5.0%) in a Placebo-Controlled Clinical Study of Metformin Hydrochloride Tablets Monotherapy* *Reactions that were more common in metformin hydrochloride tablets- than placebo- treated patients.Metformin Hydrochloride Tablets Monotherapy n = 141Placebo n = 145Adverse Reaction% of PatientsDiarrhea53.211.7Nausea/Vomiting25.58.3Flatulence12.15.5Asthenia9.25.5Indigestion7.14.1Abdominal Discomfort6.44.8Headache5.74.8Diarrhea led to discontinuation of study medication in 6% of patients treated with metformin hydrochloride tablets. Additionally, the following adverse reactions were reported in1.0-5.0% of metformin hydrochloride tablets patients and were more commonly reported with metformin hydrochloride tablets than placebo: abnormal stools, hypoglycemia, myalgia, lightheaded, dyspnea, nail disorder, rash, sweating increased, taste disorder, chest discomfort, chills, flu syndrome, flushing, palpitation. In worldwide clinical trials over 900 patients with type 2 diabetes have been treated with metformin hydrochloride extended-release tablets in placebo- and active-controlled studies. In placebo-controlled trials, 781 patients were administered metformin hydrochloride extended-release tablets and 195 patients received placebo. Adverse reactions reported in greater than 5% of the metformin hydrochloride extendedrelease tablets patients, and that were more common in metformin hydrochloride extended-release tablets - than placebo-treated patients, are uled in
Table 12
. Table 12. Most Common Adverse Reactions (>5.0%) in a Placebo-Controlled Studies of Metformin Hdyrochloride Extended-release Tablets* * Reactions that were more common in metformin hydrochloride extended-release tablets - than placebo-treated patientsMetformin Hydrochloride Extended-release Tablets n=781Placebo n=195Adverse Reaction% of PatientsDiarrhea9.62.6Nausea/Vomiting6.51.5Diarrhea led to discontinuation of study medication in 0.6% of patients treated with metformin hydrochloride extended-release tablets. Additionally, the following adverse reactions were reported in5.0% of metformin hydrochloride extendedrelease tablets patients and were more commonly reported with metformin hydrochloride extended-release tablets than placebo: abdominal pain, constipation, distention abdomen, dyspepsia/heartburn, flatulence, dizziness, headache, upper respiratory infection, taste disturbance.
Pediatric Patients
In clinical trials with metformin hydrochloride tablets in pediatric patients with type 2 diabetes, the profile of adverse reactions was similar to that observed in adults.
Overdosage
Overdose of metformin hydrochloride has occured, including ingestion of amounts greater than 50 grams. Hypoglycemia was reported in approximately 10% of cases, but no causal association with metformin hydrochloride has been established. Lactic acidosis has been reported in approximately 32% of metformin overdose cases (see
WARNINGS
). Metformin is dialyzable with a clearance of up to 170 mL/min under good hemodynamic conditions. Therefore, hemodialysis may be useful for removal of accumulated drug from patients in whom metformin overdosage is suspected.
Dosage & Administration
Metformin hydrochloride tablets should be given in divided doses with meals while metformin hydrochloride extended-release tablets should generally be given once daily with the evening meal. Metformin hydrochloride tablets or metformin hydrochloride extended-release tablets should be started at a low dose, with gradual dose escalation, both to reduce gastrointestinal side effects and to permit identification of the minimum dose required for adequate glycemic control of the patient. During treatment initiation and dose titration (see
Recommended Dosing Schedule
), fasting plasma glucose should be used to determine the therapeutic response to metformin hydrochloride tablets or metformin hydrochloride extended-release tablets and identify the minimum effective dose for the patient. Thereafter, glycosylated hemoglobin should be measured at intervals of approximately three months. The therapeutic goal should be to decrease both fasting plasma glucose and glycosylated hemoglobin levels to normal or near normal by using the lowest effective dose of metformin hydrochloride tablets or metformin hydrochloride extended-release tablets, either when used as monotherapy or in combination with sulfonylurea or insulin. Monitoring of blood glucose and glycosylated hemoglobin will also permit detection of primary failure, i.e., inadequate lowering of blood glucose at the maximum recommended dose of medication, and secondary failure, i.e., loss of an adequate blood glucose lowering response after an initial period of effectiveness. Short-term administration of metformin hydrochloride tablets or metformin hydrochloride extended-release tablets may be sufficient during periods of transient loss of control in patients usually well-controlled on diet alone. Metformin hydrochloride extended-release tablets must be swallowed whole and never crushed or chewed. Occasionally, the inactive ingredients of metformin hydrochloride extended-release will be eliminated in the feces as a soft, hydrated mass. (See Patient Information printed separately.)
Recommended Dosing Schedule
Adults - In general, clinically significant responses are not seen at doses below 1500 mg per day. However, a lower recommended starting dose and gradually increased dosage is advised to minimize gastrointestinal symptoms. The usual starting dose of metformin hydrochloride tablets is 500 mg twice a day or 850 mg once a day, given with meals. Dosage increases should be made in increment of 500 mg weekly or 850 mg every 2 weeks, up to a total of 2000 mg per day, given in divided doses. Patients can also be titrated from 500 mg twice a day to 850 mg twice a day after 2 weeks. For those patients requiring additional glycemic control, metformin hydrochloride tablets may be given to a maximum daily dose of 2550 mg per day. Doses above 2000 mg may be better tolerated given three times a day with meals. The usual starting dose of metformin hydrochloride extended-release tablets is 500 mg once daily with the evening meal. Dosage increases should be made in increments of 500 mg weekly, up to a maximum of 2000 mg once daily with the evening meal. If glycemic control is not achieved on metformin hydrochloride extended-release tablets 2000 mg once daily, a trial of metformin hydrochloride extended-release tablets 1000 mg twice daily should be considered. If higher doses of metformin hydrochloride tablets are required, metformin hydrochloride tablets should be used at total daily doses up to 2550 mg administered in divided daily doses, as described above. (See
CLINICAL PHARMACOLOGY, Clinical Studies
.) In a randomized trial, patients currently treated with metformin hydrochloride tablets were switched to metformin hydrochloride extended-release tablets. Results of this trial suggest that patients receiving metformin hydrochloride tablets treatment may be safely switched to metformin hydrochloride extended-release tablets once daily at the same total daily dose, up to 2000 mg once daily. Following a switch from metformin hydrochloride tablets to metformin hydrochloride extended-release tablets, glycemic control should be closely monitored and dosage adjustments made accordingly (see
CLINICAL PHARMACOLOGY, Clinical Studies
). Pediatrics - The usual starting dose of metformin hydrochloride tablets is 500 mg twice a day, given with meals. Dosage increases should be made in increments of 500 mg weekly up to a maximum of 2000 mg per day, given in divided doses. Safety and effectiveness of metformin hydrochloride extended-release tablets in pediatric patients have not been established.
Transfer from Other Antidiabetic Therapy
When transferring patients from standard oral hypoglycemic agents other than chlorpropamide to metformin hydrochloride tablets or metformin hydrochloride extended-release tablets, no transition period generally is necessary. When transferring patients from chlorpropamide, care should be exercised during the first two weeks because of the prolonged retention of chlorpropamide in the body, leading to overlapping drug effects and possible hypoglycemia.
Concomitant Metformin Hydrochloride Tablets or Metformin Hydrochloride Extended-release Tablets and Oral Sulfonylurea Therapy in Adult Patients
If patients have not responded to four weeks of the maximum dose of metformin hydrochloride tablets or metformin hydrochloride extended-release tablets monotherapy, consideration should be given to gradual addition of an oral sulfonylurea while continuing metformin hydrochloride tablets or metformin hydrochloride extendedrelease tablets at the maximum dose, even if prior primary or secondary failure to a sulfonylurea has occurred. Clinical and pharmacokinetic drug-drug interaction data are currently available only for metformin plus glyburide (glibenclamide). With concomitant metformin hydrochloride tablets or metformin hydrochloride extended-release tablets and sulfonylurea therapy, the desired control of blood glucose may be obtained by adjusting the dose of each drug. However, attempts should be made to identify the minimum effective dose of each drug to achieve this goal. With concomitant metformin hydrochloride tablets or metformin hydrochloride extended-release tablets and sulfonylurea therapy, the risk of hypoglycemia associated with sulfonylurea therapy continues and may be increased. Appropriate precautions should be taken. (See Package Insert of the respective sulfonylurea.) If patients have not satisfactorily responded to one to three months of concomitant therapy with the maximum dose of metformin hydrochloride tablets or metformin hydrochloride extended-release tablets and the maximum dose of an oral sulfonylurea, consider therapeutic alternatives including switching to insulin with or without metformin hydrochloride tablets or metformin hydrochloride extended-release tablets.
Concomitant Metformin Hydrochloride Tablets or Metformin Hydrochloride Extended-release Tablets and Insulin Therapy in Adult Patients
The current insulin dose should be continued upon initiation of metformin hydrochloride tablets or metformin hydrochloride extended-release tablets therapy. Metformin hydrochloride tablets or metformin hydrochloride extended-release tablets should be initiated at 500 mg once daily in patients on insulin therapy. For patients not responding adequately, the dose of metformin hydrochloride tablets or metformin hydrochloride extended-release tablets should be increased by 500 mg after approximately 1 week and by 500 mg every week thereafter until adequate glycemic control is achieved. The maximum recommended daily dose is 2500 mg for metformin hydrochloride tablets and 2000 mg for metformin hydrochloride extended-release tablets. It is recommended that the insulin dose be decreased by 10% to 25% when fasting plasma glucose concentrations decrease to less than 120 mg/dL in patients receiving concomitant insulin and metformin hydrochloride tablets or metformin hydrochloride extended-release tablets. Further adjustment should be individualized based on glucose-lowering response.
Specific Patient Populations
Metformin hydrochloride tablets or metformin hydrochloride extended-release tablets are not recommended for use in pregnancy. Metformin hydrochloride tablets are not recommended in patients below the age of 10 years. Metformin hydrochloride extended- release tablets are not recommended in pediatric patients (below the age of 17 years). The initial and maintenance dosing of metformin hydrochloride tablets or metformin hydrochloride extended-release tablets should be conservative in patients with advanced age, due to the potential for decreased renal function in this population. Any dosage adjustment should be based on a careful assessment of renal function. Generally, elderly, debilitated, and malnourished patients should not be titrated to the maximum dose of metformin hydrochloride tablets or metformin hydrochloride extended-release tablets. Monitoring of renal function is necessary to aid in prevention of lactic acidosis, particularly in the elderly. (See
WARNINGS
.)
How Supplied
Metformin hydrochloride tablets are available as: 500 mg Bottles of 100 NDC 62037-674-01 500 mg Bottles of 500 NDC 62037-674-05 500 mg Bottles of 1000 NDC 62037-674-10 850 mg Bottles of 100 NDC 62037-675-01 850 mg Bottles of 500 NDC 62037-675-05 850 mg Bottles of 1000 NDC 62037-675-10 1000 mg Bottles of 100 NDC 62037-676-01 1000 mg Bottles of 500 NDC 62037-676-05 1000 mg Bottles of 1000 NDC 62037-676-10 Metformin hydrochloride 500 mg tablets are round, white to off-white, film coated tablets debossed withAndrx 674on one side and500debossed on the other side. Metformin hydrochloride 850 mg tablets are round, white to off-white, film coated tablets debossed withAndrx 675on one side and850debossed on the other side. Metformin hydrochloride 1000 mg tablets are oval, white to off-white, film coated tablets withAndrx 676debossed on one side and bisected1000on the other side. Metformin hydrochloride extended-release tablets are available as: 500 mg Bottles of 100 NDC 62037-571-01 500 mg Bottles of 500 NDC 62037-571-05 500 mg Bottles of 1000 NDC 62037-571-10 750 mg Bottles of 100 NDC 62037-577-01 750 mg Bottles of 500 NDC 62037-577-05 750 mg Bottles of 1000 NDC 62037-577-10 Metformin hydrochloride extended-release 500 mg tablets are white to off-white, capsule shaped tablets, debossed with theand571on one side and500on the other side. Metformin hydrochloride extended-release 750 mg tablets are light yellow, capsule shaped tablets, debossed withand577on one side and750on opposite side.
Storage And Handling
Store at controlled room temperature 20(68[See USP.] Dispense in light-resistant containers.
Package Label.principal Display Panel Section
DRUG: Metformin Hydrochloride GENERIC: Metformin Hydrochloride DOSAGE: TABLET, EXTENDED RELEASE ADMINSTRATION: ORAL NDC: 49349-707-02 STRENGTH:500 mg COLOR: white SHAPE: OVAL SCORE: No score SIZE: 20 mm IMPRINT: 30 QTY: 30![]()
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