Methimazole (methimazole 10 mg) Dailymed
Generic: methimazole
IMPRINT: E 210
SHAPE: round
COLOR: white SCORE: 2
All Imprints
methimazole 5 mg - e 205 round white
methimazole 10 mg - e 210 round white
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Description
Methimazole Tablets USP (1- methylimidazole-2-thiol) is a white, crystalline substance that is freely soluble in water.
It differs chemically from the drugs of the thiouracil series primarily because it has a 5- instead of a 6-membered ring.
Each tablet contains 5 or 10 mg (43.8 or 87.6 μmol) methimazole, an orally administered antithyroid drug.
Each tablet also contains lactose monohydrate, NF, colloidal silicon dioxide, NF, talc, USP, pregelatinized starch, NF,
anhydrous lactose, NF, and magnesium stearate, NF. The molecular weight is 114.16, and the molecular formula
is C4H6N2S. The structural formula is as follows:
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Clinical Pharmacology
Methimazole inhibits the synthesis of thyroid hormones and thus is effective in the treatment of hyperthyroidism.
The drug does not inactivate existing thyroxine and triiodothyronine that are stored in the thyroid or circulating in
the blood nor does it interfere with the effectiveness of thyroid hormones given by mouth or by injection.
The actions and use of methimazole are similar to those of propylthiouracil. On a weight basis, the drug is at least 10
times as potent as propylthiouracil, but methimazole may be less consistent in action. Methimazole is readily
absorbed from the gastrointestinal tract. It is metabolized rapidly and requires frequent administration. Methimazole is
excreted in the urine. In laboratory animals, various regimens that continuously suppress thyroid function and
thereby increase TSH secretion result in thyroid tissue hypertrophy. Under such conditions, the appearance of thyroid
and pituitary neoplasms has also been reported. Regimens that have been studied in this regard include
antithyroid agents as well as dietary iodine deficiency, subtotal thyroidectomy, implantation of autonomous
thyrotropic hormone-secreting pituitary tumors, and administration of chemical goitrogens.
Indications And Usage
Methimazole is indicated in the medical treatment of hyperthyroidism. Long-term therapy may lead to remission of the
disease. Methimazole may be used to ameliorate hyperthyroidism in preparation for subtotal thyroidectomy or
radioactive iodine therapy. Methimazole is also used when thyroidectomy is contraindicated or not advisable.
Contraindications
Methimazole is contraindicated in the presence of hypersensitivity to the drug and in nursing mothers because the
drug is excreted in milk.
Warnings
Agranulocytosis is potentially a serious side effect. Patients should be instructed to report to their physicians any symptoms
of agranulocytosis, such as fever or sore throat. Leukopenia, thrombocytopenia, and aplastic anemia (pancytopenia) may also occur.
The drug should be discontinued in the presence of agranulocytosis, aplastic anemia (pancytopenia), hepatitis, or exfoliative dermatitis.
The patient"s bone marrow function should be monitored. Due to the similar hepatic toxicity profiles of methimazole
and propylthiouracil, attention is drawn to the severe hepatic reactions which have occurred with both drugs. There have
been rare reports of fulminant hepatitis, hepatic necrosis, encephalopathy, and death. Symptoms suggestive of
hepatic dysfunction (anorexia, pruritus, right upper quadrant pain, etc) should prompt evaluation of liver function. Drug
treatment should be discontinued promptly in the event of clinically significant evidence of liver abnormality including
hepatic transaminase values exceeding 3 times the upper limit of normal. Methimazole can cause fetal harm when administered
to a pregnant woman. Methimazole readily crosses the placental membranes and can induce goiter and even cretinism
in the developing fetus. In addition, rare instances of congenital defects: aplasia cutis, as manifested by scalp
defects; esophageal atresia with tracheoesophageal fistula; and choanal atresia with absent/ hypoplastic nipples,
have occurred in infants born to mothers who received methimazole during pregnancy. If methimazole is used
during pregnancy or if the patient becomes pregnant while taking this drug, the patient should be warned of the
potential hazard to the fetus. Since the above congenital defects have been reported in offspring of patients treated
with methimazole, it may be appropriate to use other agents in pregnant women requiring treatment for hyperthyroidism.
Postpartum patients receiving methimazole should not nurse their babies.
Precautions
General
Patients who receive methimazole should be under close surveillance and should be cautioned to report immediately
any evidence of illness, particularly sore throat, skin eruptions, fever, headache, or general malaise. In such
cases, white-blood cell and differential counts should be made to determine whether agranulocytosis has developed.
Particular care should be exercised with patients who are receiving additional drugs known to cause agranulocytosis
Laboratory Tests - Because methimazole may cause hypoprothrombinemia and bleeding, prothrombin time
should be monitored during therapy with the drug, especially before surgical procedures (see General under PRECAUTIONS).
Periodic monitoring of thyroid function is warranted, and the finding of an elevated TSH warrants a decrease in the
dosage of methimazole.
Drug Interactions
Anticoagulants (oral): The activity of oral anticoagulants may be potentiated by antivitamin- K activity attributed to methimazole.
b−adrenergic blocking agents:Hyperthyroidism may cause increased clearance of beta blockers with a high extraction
ratio. A dose reduction of betaadrenergic blockers may be needed when a hyperthyroid patient becomes euthyroid.
Digitalis glycosides: Serum digitalis levels may be increased when hyperthyroid patients on a stable digitalis
glycoside regimen become euthyroid; reduced dosage of digitalis glycosides may be required.
Theophylline:
Theophylline clearance may decrease when hyperthyroid patients on a stable theophylline regimen become euthyroid; a reduced
dose of theophylline may be needed.
Carcinogenesis, Mutagenesis, Impairment of Fertility
In a 2 year study, rats were given methimazole at doses of 0.5, 3, and 18 mg/kg/day. These doses were 0.3, 2, and 12
times the 15 mg/day maximum human maintenance dose (when calculated on the basis of surface area). Thyroid
hyperplasia, adenoma, and carcinoma developed in rats at the two higher doses. The clinical significance of these findings
is unclear.
Pregnancy
Pregnancy Category D - See WARNINGS - Methimazole used judiciously is an effective drug in hyperthyroidism complicated
by pregnancy. In many pregnant women, the thyroid dysfunction diminishes as the pregnancy proceeds; consequently,
a reduction in dosage may be possible. In some instances, use of methimazole can be discontinued 2 or 3
weeks before delivery.
Nursing Mothers
The drug appears in human breast milk and its use is contraindicated in nursing mothers (see WARNINGS).
Pediatric Use
See DOSAGE AND ADMINISTRATION.
Adverse Reactions
Major adverse reactions (which occur with much less frequency than the minor adverse reactions) include inhibition of myelopoiesis
(agranulocytosis, granulocytopenia, and thrombocytopenia), aplastic anemia, drug fever, a lupuslike syndrome,
insulin autoimmune syndrome (which can result in hypoglycemic coma), hepatitis (jaundice may persist for several
weeks after discontinuation of the drug), periarteritis, and hypoprothrombinemia. Nephritis occurs very rarely.
Minor adverse reactions include skin rash, urticaria, nausea, vomiting, epigastric distress, arthralgia, paresthesia,
loss of taste, abnormal loss of hair, myalgia, headache, pruritus, drowsiness, neuritis, edema, vertigo,
skin pigmentation, jaundice, sialadenopathy, and lymphadenopathy. It should be noted that about 10% of patients with untreated
hyperthyroidism have leukopenia (white-blood-cell count of less than 4,000/mm3), often with relative granulopenia.
Overdosage
Signs and Symptoms -
-
Symptoms may include nausea, vomiting, epigastric distress, headache, fever, joint pain, pruritus, and edema.
Aplastic anemia (pancytopenia) or agranulocytosis may be manifested in hours to days. Less frequent events are hepatitis,
nephrotic syndrome, exfoliative dermatitis, neuropathies, and CNS stimulation or depression. Although not
well studied, methimazoleinduced agranulocytosis is generally associated with doses of 40 mg or more in
patients older than 40 years of age.
No information is available on the median lethal dose of the drug or the concentration of methimazole in biologic fluids
associated with toxicity and/or death. Treatment - To obtain up-todate - To obtain up-todate information about the
treatment of overdose, a good resource is your certified Regional Poison Control Center. Telephone numbers of
certified poison control centers are uled in the Physicians" Desk Reference (PDR). In managing overdosage,
. In managing overdosage, consider the possibility of multiple drug overdoses, interaction among drugs, and
unusual drug kinetics in your patient. Protect the patient"s airway and support ventilation and perfusion. Meticulously monitor
and maintain, within acceptable limits, the patient"s vital signs, blood gases, serum electrolytes, etc. The patient"s
bone marrow function should be monitored. Absorption of drugs from the gastrointestinal tract may be decreased by giving
activated charcoal, which, in many cases, is more effective than emesis or lavage; consider charcoal instead of or
in addition to gastric emptying. Repeated doses of charcoal over time may hasten elimination of some drugs that have
been absorbed. Safeguard the patient"s airway when employing gastric emptying or charcoal. Forced diuresis, peritoneal
dialysis, hemodialysis, or charcoal hemoperfusion have not been established as beneficial for an overdose of methimazole.
Dosage And Administration
Methimazole is administered orally. Tablets are usually given in 3 equal doses at approximately 8-hour intervals.
Adult - The initial daily dosage
- The initial daily dosage is 15 mg for mild hyperthyroidism, 30 to 40 mg for moderately evere hyperthyroidism and 60 mg for severe
hyperthyroidism, divided into 3 doses at 8-hour intervals. The maintenance dosage is 5 to 5 mg daily.
Pediatric - Initially, the daily
- Initially, the daily dosage is 0.4 mg/kg of body weight divided into 3 doses and given at 8-hour intervals.
The maintenance dosage is approximately 1⁄2 of the initial dose.
How Supplied
Methimazole Tablets are available in:
The 5 mg tablets are white, round, biconvex, beveled tablets, scored on one side and imprinted “E” over “205”
on the other. They are available as follows:
Bulercards of 30 tablets.
10 mg: White, round, biconvex, beveled tablets, scored on one side and debossed “E” over “210” on the other side and supplied as:
Bulercards of 30 tablets
Store at 20°-25°C (68°- 77°F)[see USP Controlled Room Temperature].
Dispense contents in a tight, light resistant container as defined in the USP with a child-resistant closure, as required.
KEEP THIS AND ALL MEDICATION OUT OF THE REACH OF CHILDREN.
References
Sandoz Inc.
Princeton, NJ 08540
Rev. 03/06
OS7631
MF0205REV03/06
MG #16035
Principal Display Panel
Methimazole Tablets,
USP 5mg
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Principal Display Panel
Methimazole Tablets, USP 10mg
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