Carbidopa and Levodopa (carbidopa 25 mg levodopa 100 mg) Dailymed
Generic: carbidopa and levodopa
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Description
Carbidopa-levodopa extended-release tablet is a combination of carbidopa and levodopa for the treatment of Parkinson's disease and syndrome. Carbidopa, an inhibitor of aromatic amino acid decarboxylation, is a white, crystalline compound, slightly soluble in water, with a molecular weight of 244.3. It is designated chemically as (—)-L-α-hydrazino-α-methyl-β-(3,4-dihydroxy-benzene) propanoic acid monohydrate. Its empirical formula is C10H14N2O4•H2O and its structural formula is:
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Tablet content is expressed in terms of anhydrous carbidopa, which has a molecular weight of 226.3.
Levodopa, an aromatic amino acid, is a white, crystalline compound, slightly soluble in water, with a molecular weight of 197.2. It is designated chemically as (—)-L-α-amino-β-(3,4-dihydroxybenzene) propanoic acid. Its empirical formula is C9H11NO4 and its structural formula is:
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Carbidopa-levodopa extended-release tablet is supplied as a tablet containing either 50 mg of carbidopa and 200 mg of levodopa, or 25 mg of carbidopa and 100 mg of levodopa. Inactive ingredients: hydroxypropyl cellulose, lake blend purple (contains FD&C Red No. 40, FD &C Blue No. 2) and magnesium stearate.
The 25 mg/100 mg and the 50 mg/200 mg tablets are supplied as an oval, convex, compressed tablet that is purple colored. The carbidopa-levodopa extended-release tablet is a polymeric-based drug delivery system that controls the release of carbidopa and levodopa as it slowly erodes. Carbidopa-levodopa extended-release tablet, 25 mg/100 mg is available to facilitate titration and as an alternative to the half-tablet of carbidopa-levodopa extended-release tablet, 50 mg/200 mg.
Clinical Pharmacology
Mechanism of Action
Parkinson's disease is a progressive, neurodegenerative disorder of the extrapyramidal nervous system affecting the mobility and control of the skeletal muscular system. Its characteristic features include resting tremor, rigidity, and bradykinetic movements. Symptomatic treatments, such as levodopa therapies, may permit the patient better mobility.
Current evidence indicates that symptoms of Parkinson's disease are related to depletion of dopamine in the corpus striatum. Administration of dopamine is ineffective in the treatment of Parkinson's disease apparently because it does not cross the blood-brain barrier. However, levodopa, the metabolic precursor of dopamine, does cross the blood-brain barrier, and presumably is converted to dopamine in the brain. This is thought to be the mechanism whereby levodopa relieves symptoms of Parkinson's disease.
Pharmacodynamics
When levodopa is administered orally it is rapidly decarboxylated to dopamine in extracerebral tissues so that only a small portion of a given dose is transported unchanged to the central nervous system. For this reason, large doses of levodopa are required for adequate therapeutic effect and these may often be accompanied by nausea and other adverse reactions, some of which are attributable to dopamine formed in extracerebral tissues.
Since levodopa competes with certain amino acids for transport across the gut wall, the absorption of levodopa may be impaired in some patients on a high protein diet.
Carbidopa inhibits decarboxylation of peripheral levodopa. It does not cross the blood-brain barrier and does not affect the metabolism of levodopa within the central nervous system.
Since its decarboxylase inhibiting activity is limited to extracerebral tissues, administration of carbidopa with levodopa makes more levodopa available for transport to the brain.
Patients treated with levodopa therapy for Parkinson's disease may develop motor fluctuations characterized by end-of-dose failure, peak dose dyskinesia, and akinesia. The advanced form of motor fluctuations ('on-off' phenomenon) is characterized by unpredictable swings from mobility to immobility. Although the causes of the motor fluctuations are not completely understood, in some patients they may be attenuated by treatment regimens that produce steady plasma levels of levodopa.
Carbidopa-levodopa extended-release tablet contains either 50 mg of carbidopa and 200 mg of levodopa, or 25 mg of carbidopa and 100 mg of levodopa in an extended-release dosage form designed to release these ingredients over a 4- to 6-hour period. With carbidopa-levodopa extended-release tablet there is less variation in plasma levodopa levels than with carbidopa-levodopa tablets, the conventional formulation. However, carbidopa-levodopa extended-release tablet is less systemically bioavailable than carbidopa-levodopa tablets and may require increased daily doses to achieve the same level of symptomatic relief as provided by carbidopa-levodopa tablets.
In clinical trials, patients with moderate to severe motor fluctuations who received carbidopa-levodopa extended-release tablet did not experience quantitatively significant reductions in 'off' time when compared to carbidopa-levodopa tablets. However, global ratings of improvement as assessed by both patient and physician were better during therapy with carbidopa-levodopa extended-release tablet than with carbidopa-levodopa tablets. In patients without motor fluctuations, carbidopa-levodopa extended-release tablet, under controlled conditions, provided the same therapeutic benefit with less frequent dosing when compared to carbidopa-levodopa tablets.
Pharmacokinetics
Carbidopa reduces the amount of levodopa required to produce a given response by about 75% and, when administered with levodopa, increases both plasma levels and the plasma half-life of levodopa, and decreases plasma and urinary dopamine and homovanillic acid.
Elimination half-life of levodopa in the presence of carbidopa is about 1.5 hours. Following carbidopa-levodopa extended-release tablet, the apparent half-life of levodopa may be prolonged because of continuous absorption.
In healthy elderly subjects (56-67 years old) the mean time-to-peak concentration of levodopa after a single dose of carbidopa-levodopa extended-release tablet, 50 mg/200 mg was about 2 hours as compared to 0.5 hours after standard carbidopa-levodopa tablets. The maximum concentration of levodopa after a single dose of carbidopa-levodopa extended-release tablet was about 35% of the standard carbidopa- levodopa tablets (1151 vs. 3256 ng/mL). The extent of availability of levodopa from carbidopa-levodopa extended-release tablet was about 70-75% relative to intravenous levodopa or standard carbidopa-levodopa tablets in the elderly. The absolute bioavailability of levodopa from carbidopa-levodopa extended-release tablet (relative to I.V.) in young subjects was shown to be only about 44%. The extent of availability and the peak concentrations of levodopa were comparable in the elderly after a single dose and at steady state after t.i.d. administration of carbidopa-levodopa extended-release tablet, 50 mg/200 mg. In elderly subjects, the average trough levels of levodopa at steady state after the extended-release tablet were about 2 fold higher than after the standard carbidopa-levodopa tablets (163 vs. 74 ng/mL).
In these studies, using similar total daily doses of levodopa, plasma levodopa concentrations with carbidopa-levodopa extended-release tablet fluctuated in a narrower range than with carbidopa-levodopa tablets. Because the bioavailability of levodopa from carbidopa-levodopa extended-release tablet relative to carbidopa-levodopa tablets is approximately 70-75%, the daily dosage of levodopa necessary to produce a given clinical response with the extended-release formulation will usually be higher.
The extent of availability and peak concentrations of levodopa after a single dose of carbidopa-levodopa extended-release tablet, 50 mg/200 mg increased by about 50% and 25%, respectively, when administered with food.
At steady state, the bioavailability of carbidopa from carbidopa-levodopa tablets is approximately 99% relative to the concomitant administration of carbidopa and levodopa. At steady state, carbidopa bioavailability from carbidopa-levodopa extended-release tablet, 50 mg/200 mg is approximately 58% relative to that from carbidopa-levodopa tablets.
Pyridoxine hydrochloride (vitamin B6), in oral doses of 10 mg to 25 mg, may reverse the effects of levodopa by increasing the rate of aromatic amino acid decarboxylation. Carbidopa inhibits this action of pyridoxine.
Indications And Usage
Carbidopa-levodopa extended-release tablet is indicated in the treatment of the symptoms of idiopathic Parkinson's disease (paralysis agitans), postencephalitic parkinsonism, and symptomatic parkinsonism which may follow injury to the nervous system by carbon monoxide intoxication and/or manganese intoxication.
Contraindications
Nonselective MAO inhibitors are contraindicated for use with carbidopa-levodopa extended-release tablet. These inhibitors must be discontinued at least two weeks prior to initiating therapy with carbidopa-levodopa extended-release tablet. Carbidopa-levodopa extended-release tablet may be administered concomitantly with the manufacturer's recommended dose of an MAO inhibitor with selectivity for MAO type B (e.g., selegiline HCI) (See PRECAUTIONS: Drug Interactions ).
Carbidopa-levodopa extended-release tablet is contraindicated in patients with known hypersensitivity to any component of this drug and in patients with narrow-angle glaucoma.
Because levodopa may activate a malignant melanoma, carbidopa-levodopa extended-release tablet should not be used in patients with suspicious, undiagnosed skin lesions or a history of melanoma.
Warnings
When patients are receiving levodopa without a decarboxylase inhibitor, levodopa must be discontinued at least twelve hours before carbidopa-levodopa extended-release tablet is started. In order to reduce adverse reactions, it is necessary to individualize therapy. Carbidopa-levodopa extended-release tablet should be substituted at a dosage that will provide approximately 25% of the previous levodopa dosage (see DOSAGE AND ADMINISTRATION ).
Carbidopa does not decrease adverse reactions due to central effects of levodopa. By permitting more levodopa to reach the brain, particularly when nausea and vomiting is not a dose-limiting factor, certain adverse CNS effects, e.g., dyskinesias, will occur at lower dosages and sooner during therapy with carbidopa-levodopa extended-release than with levodopa alone.
Patients receiving carbidopa-levodopa extended-release tablet may develop increased dyskinesias compared to carbidopa-levodopa tablets. Dyskinesias are a common side effect of carbidopa-levodopa treatment. The occurrence of dyskinesias may require dosage reduction.
As with levodopa, carbidopa-levodopa extended-release tablet may cause mental disturbances. These reactions are thought to be due to increased brain dopamine following administration of levodopa. All patients should be observed carefully for the development of depression with concomitant suicidal tendencies. Patients with past or current psychoses should be treated with caution.
Carbidopa-levodopa extended-release tablet should be administered cautiously to patients with severe cardiovascular or pulmonary disease, bronchial asthma, renal, hepatic or endocrine disease.
As with levodopa, care should be exercised in administering carbidopa-levodopa extended-release tablet to patients with a history of myocardial infarction who have residual atrial, nodal, or ventricular arrhythmias. In such patients, cardiac function should be monitored with particular care during the period of initial dosage adjustment, in a facility with provisions for intensive cardiac care.
As with levodopa, treatment with carbidopa-levodopa extended-release tablet may increase the possibility of upper gastrointestinal hemorrhage in patients with a history of peptic ulcer.
Neuroleptic Malignant Syndrome (NMS)
Sporadic cases of a symptom complex resembling NMS have been reported in association with dose reductions or withdrawal of carbidopa-levodopa tablets and carbidopa-levodopa extended-release tablets.
Therefore, patients should be observed carefully when the dosage of carbidopa-levodopa extended-release tablet is reduced abruptly or discontinued, especially if the patient is receiving neuroleptics.
NMS is an uncommon but life-threatening syndrome characterized by fever or hyperthermia. Neurological findings, including muscle rigidity, involuntary movements, altered consciousness, mental status changes; other disturbances, such as autonomic dysfunction, tachycardia, tachypnea, sweating, hyper- or hypotension; laboratory findings, such as creatine phosphokinase elevation, leukocytosis, myoglobinuria, and increased serum myoglobin have been reported.
The early diagnosis of this condition is important for the appropriate management of these patients. Considering NMS as a possible diagnosis and ruling out other acute illnesses (e.g., pneumonia, systemic infection, etc.) is essential. This may be especially complex if the clinical presentation includes both serious medical illness and untreated or inadequately treated extrapyramidal signs and symptoms (EPS). Other important considerations in the differential diagnosis include central anticholinergic toxicity, heat stroke, drug fever, and primary central nervous system (CNS) pathology.
The management of NMS should include: 1) intensive symptomatic treatment and medical monitoring and 2) treatment of any concomitant serious medical problems for which specific treatments are available. Dopamine agonists, such as bromocriptine, and muscle relaxants, such as dantrolene, are often used in the treatment of NMS; however, their effectiveness has not been demonstrated in controlled studies.
Precautions
General
As with levodopa, periodic evaluations of hepatic, hematopoietic, cardiovascular, and renal function are recommended during extended therapy.
Patients with chronic wide-angle glaucoma may be treated cautiously with carbidopa-levodopa extended-release tablet provided the intraocular pressure is well-controlled and the patient is monitored carefully for changes in intraocular pressure during therapy.
Dopaminergic agents, including levodopa, may be associated with somnolence and very rarely episodes of sudden onset of sleep. In some cases, these episodes may occur without awareness or warning during daily activities. Patients must be informed of this and advised to exercise caution while driving or operating machines while being treated with dopaminergic agents, including levodopa. Patients who have experience somnolence and/or an episode of sudden sleep onset must refrain from driving or operating machines (see Information for Patients ).
Melanoma
Epidemiological studies have shown that patients with Parkinson's disease have a higher risk (2- to approximately 6-fold higher) of developing melanoma than the general population. Whether the increased risk observed was due to Parkinson's disease or other factors, such as drugs used to treat Parkinson's disease, is unclear.
For the reasons stated above, patients and providers are advised to monitor for melanomas frequently and on a regular basis when using carbidopa-levodopa extended-release tablet for any indication. Ideally, periodic skin examinations should be performed by appropriately qualified individuals (e.g., dermatologists).
Information for Patients
The patient should be informed that carbidopa-levodopa extended-release tablet is an extended-release formulation of carbidopa-levodopa which releases these ingredients over a 4- to 6-hour period. It is important that carbidopa-levodopa extended-release tablet be taken at regular intervals according to the schedule outlined by the physician. The patient should be cautioned not to change the prescribed dosage regimen and not to add any additional antiparkinson medications, including other carbidopa-levodopa preparations, without first consulting the physician.
If abnormal involuntary movements appear or get worse during treatment with carbidopa-levodopa extended-release tablet, the physician should be notified, as dosage adjustment may be necessary.
Patients should be advised that sometimes the onset of effect of the first morning dose of carbidopa-levodopa extended-release tablet may be delayed for up to 1 hour compared with the response usually obtained from the first morning dose of carbidopa-levodopa tablets. The physician should be notified if such delayed responses pose a problem in treatment.
Patients should be advised that, occasionally, dark color (red, brown, or black) may appear in saliva, urine, or sweat after ingestion of carbidopa-levodopa extended-release tablet. Although the color appears to be clinically insignificant, garments may become discolored.
The patient should be informed that a change in diet to foods that are high in protein may delay the absorption of levodopa and may reduce the amount taken up in the circulation. Excessive acidity also delays stomach emptying, thus delaying the absorption of levodopa. Iron salts (such as in multivitamin tablets) may also reduce the amount of levodopa available to the body. The above factors may reduce the clinical effectiveness of the levodopa or carbidopa-levodopa therapy.
Patients must be advised that the whole or half tablet should be swallowed without chewing or crushing.
Patients should be alerted to the possibility of sudden onset of sleep during daily activities, in some cases without awareness or warning signs, when they are dopaminergic agents, including levodopa. Patients should be advised to exercise caution while driving or operating machinery and that if they have experience somnolence and/or sudden sleep onset, they must refrain from these activities. (See PRECAUTIONS: General .)
There have been reports of patients experiencing intense urges to gamble, increased sexual urges, and other intense urges and the inability to control these urges while taking one or more of the medications that increase central dopaminergic tone, that are generally used for the treatment of Parkinson's disease, including carbidopa-levodopa extended-release tablet. Although it is not proven that the medications caused these events, these urges were reported to have stopped in some cases when the dose was reduced or the medication was stopped. Prescribers should ask patients about the development of new or increased gambling urges, sexual urges or other urges while being treated with carbidopa-levodopa extended-release tablet. Patients should inform their physician if they experience new or increased gambling urges, increased sexual urges or other intense urges while taking carbidopa-levodopa extended-release tablet. Physicians should consider dose reduction or stopping the medication if a patient develops such urges while taking carbidopa-levodopa extended-release tablet.
NOTE: The suggested advice to patients being treated with carbidopa-levodopa extended-release tablet is intended to aid in the safe and effective use of this medication. It is not a disclosure of all possible adverse or intended effects.
Laboratory Tests
Abnormalities in laboratory tests may include elevations of liver function tests such as alkaline phosphatase, SGOT (AST), SGPT (ALT), lactic dehydrogenase, and bilirubin. Abnormalities in blood urea nitrogen and positive Coombs test have also been reported. Commonly, levels of blood urea nitrogen, creatinine, and uric acid are lower during administration of carbidopa-levodopa preparations than with levodopa.
Carbidopa-levodopa preparations, such as carbidopa-levodopa tablets and carbidopa-levodopa extended-release tablet, may cause a false-positive reaction for urinary ketone bodies when a test tape is used for determination of ketonuria. This reaction will not be altered by boiling the urine specimen. False-negative tests may result with the use of glucose-oxidase methods of testing for glucosuria.
Cases of falsely diagnosed pheochromocytoma in patients on carbidopa-levodopa therapy have been reported very rarely. Caution should be exercised when interpreting the plasma and urine levels of catecholamines and their metabolites in patients on levodopa or carbidopa-levodopa therapy.
Drug Interactions
Caution should be exercised when the following drugs are administered concomitantly with carbidopa-levodopa extended-release tablet.
Symptomatic postural hypotension has occurred when carbidopa-levodopa preparations were added to the treatment of patients receiving some antihypertensive drugs. Therefore, when therapy with carbidopa-levodopa extended-release tablet is started, dosage adjustment of the antihypertensive drug may be required.
For patients receiving monoamine oxidase (MAO) inhibitors (Type A or B), see CONTRAINDICATIONS . Concomitant therapy with selegiline and carbidopa-levodopa may be associated with severe orthostatic hypotension not attributable to carbidopa-levodopa alone (see CONTRAINDICATIONS ).
There have been rare reports of adverse reactions, including hypertension and dyskinesia, resulting from the concomitant use of tricyclic antidepressants and carbidopa-levodopa preparations.
Dopamine D2 receptor antagonists (e.g., phenothiazines, butyrophenones, risperidone) and isoniazid may reduce the therapeutic effects of levodopa. In addition, the beneficial effects of levodopa in Parkinson's disease have been reported to be reversed by phenytoin and papaverine. Patients taking these drugs with carbidopa-levodopa extended-release tablet should be carefully observed for loss of therapeutic response.
Iron salts may reduce the bioavailability of levodopa and carbidopa. The clinical relevance is unclear.
Although metoclopramide may increase the bioavailability of levodopa by increasing gastric emptying, metoclopramide may also adversely affect disease control by its dopamine receptor antagonistic properties.
Carcinogenesis, Mutagenesis, Impairment of Fertility
In a two-year bioassay of carbidopa-levodopa tablets, no evidence of carcinogenicity was found in rats receiving doses of approximately two times the maximum daily human dose of carbidopa and four times the maximum daily human dose of levodopa (equivalent to 8 carbidopa-levodopa extended-release tablets).
In reproduction studies with carbidopa-levodopa tablets, no effects on fertility were found in rats receiving doses of approximately two times the maximum daily human dose of carbidopa and four times the maximum daily human dose of levodopa (equivalent to 8 carbidopa-levodopa extended-release tablets).
Pregnancy
Pregnancy Category C
No teratogenic effects were observed in a study in mice receiving up to 20 times the maximum recommended human dose of carbidopa-levodopa tablets. There was a decrease in the number of live pups delivered by rats receiving approximately two times the maximum recommended human dose of carbidopa and approximately five times the maximum recommended human dose of levodopa during organogenesis. Carbidopa-levodopa tablets caused both visceral and skeletal malformations in rabbits at all doses and ratios of carbidopa/levodopa tested, which ranged from 10 times/5 times the maximum recommended human dose of carbidopa/levodopa to 20 times/10 times the maximum recommended human dose of carbidopa/levodopa.
There are no adequate or well-controlled studies in pregnant women. It has been reported from individual cases that levodopa crosses the human placental barrier, enters the fetus, and is metabolized. Carbidopa concentrations in fetal tissue appeared to be minimal. Use of carbidopa-levodopa extended-release tablet in women of childbearing potential requires that the anticipated benefits of the drug be weighed against possible hazards to mother and child.
Nursing Mothers
In a study of one nursing mother with Parkinson's disease, excretion of levodopa in human breast milk was reported. Therefore, caution should be exercised when carbidopa-levodopa extended-release tablet is administered to a nursing woman.
Pediatric Use
Safety and effectiveness in pediatric patients have not been established. Use of the drug in patients below the age of 18 is not recommended.
Adverse Reactions
In controlled clinical trials, patients predominantly with moderate to severe motor fluctuations while on carbidopa-levodopa tablets were randomized to therapy with either carbidopa-levodopa or carbidopa-levodopa extended-release tablet. The adverse experience frequency profile of carbidopa-levodopa extended-release tablet did not differ substantially from that of carbidopa-levodopa tablets, as shown in Table I.
Table I. Clinical Adverse Experiences Occurring in 1% or Greater of Patients Adverse Experience Carbidopa-LevodopaExtended-release Tablet Carbidopa-LevodopaTablets n = 491 n = 524 % %  Dyskinesia  16.5  12.2  Nausea  5.5  5.7  Hallucinations  3.9  3.2  Confusion  3.7  2.3  Dizziness  2.9  2.3  Depression  2.2  1.3  Urinary tract infection  2.2  2.3  Headache  2.0  1.9  Dream abnormalities  1.8  0.8  Dystonia  1.8  0.8  Vomiting  1.8  1.9  Upper respiratory infection  1.8  1.0  Dyspnea  1.6  0.4  'On-Off' phenomena  1.6  1.1  Back pain  1.6  0.6  Dry mouth  1.4  1.1  Anorexia  1.2  1.1  Diarrhea  1.2  0.6  Insomnia  1.2  1.0  Orthostatic hypotension  1.0  1.1  Shoulder pain  1.0  0.6  Chest pain  1.0  0.8  Muscle cramps  0.8  1.0  Paresthesia  0.8  1.1  Urinary frequency  0.8  1.1  Dyspepsia  0.6  1.1  Constipation  0.2  1.5
Abnormal laboratory findings occurring at a frequency of 1% or greater in approximately 443 patients who received carbidopa-levodopa extended-release tablet and 475 who received carbidopa-levodopa tablets during controlled clinical trials included: decreased hemoglobin and hematocrit; elevated serum glucose; white blood cells, bacteria and blood in the urine.
The adverse experiences observed in patients in uncontrolled studies were similar to those seen in controlled clinical studies.
Other adverse experiences reported overall in clinical trials in 748 patients treated with carbidopa-levodopa extended-release tablet, uled by body system in order of decreasing frequency, include:
Body as a Whole: Asthenia, fatigue, abdominal pain, orthostatic effects.
Cardiovascular: Palpitation, hypertension, hypotension, myocardial infarction.
Gastrointestinal: Gastrointestinal pain, dysphagia, heartburn.
Metabolic: Weight loss.
Musculoskeletal: Leg pain.
Nervous System/Psychiatric: Chorea, somnolence, falling, anxiety, disorientation, decreased mental acuity, gait abnormalities, extrapyramidal disorder, agitation, nervousness, sleep disorders, memory impairment.
Respiratory: Cough, pharyngeal pain, common cold.
Skin: Rash.
Special Senses: Blurred vision.
Urogenital: Urinary incontinence.
Laboratory Tests: Decreased white blood cell count and serum potassium; increased BUN, serum creatinine and serum LDH; protein and glucose in the urine.
The following adverse experiences have been reported in post-marketing experience with carbidopa-levodopa extended-release tablet:
Cardiovascular: Cardiac irregularities, syncope.
Gastrointestinal: Taste alterations, dark saliva.
Hypersensitivity: Angioedema, urticaria, pruritus, bullous lesions (including pemphigus-like reactions).
Nervous System/Psychiatric: Neuroleptic malignant syndrome (see WARNINGS ), increased tremor, peripheral neuropathy, psychotic episodes including delusions and paranoid ideation, increased libido.
Skin: Alopecia, flushing, dark sweat.
Urogenital: Dark urine.
Other adverse reactions that have been reported with levodopa alone and with various carbidopa-levodopa formulations and may occur with carbidopa-levodopa extended-release tablet are:
Cardiovascular: Phlebitis.
Gastrointestinal: Gastrointestinal bleeding, development of duodenal ulcer, sialorrhea, bruxism, hiccups, flatulence, burning sensation of tongue.
Hematologic: Hemolytic and nonhemolytic anemia, thrombocytopenia, leukopenia, agranulocytosis.
Hypersensitivity: Henoch-Schonlein purpura.
Metabolic: Weight gain, edema.
Nervous System/Psychiatric: Ataxia, depression with suicidal tendencies, dementia, euphoria, convulsions (however, a causal relationship has not been established); bradykinetic episodes, numbness, muscle twitching, blepharospasm (which may be taken as an early sign of excess dosage; consideration of dosage reduction may be made at this time), trismus, activation of latent Horner's syndrome, nightmares.
Skin: Malignant melanoma (see also CONTRAINDICATIONS ), increased sweating.
Special Senses: Oculogyric crises, mydriasis, diplopia.
Urogenital: Urinary retention, priapism.
Miscellaneous: Faintness, hoarseness, malaise, hot flashes, sense of stimulation, bizarre breathing patterns.
Laboratory Tests: Abnormalities in alkaline phosphatase, SGOT (AST), SGPT (ALT), bilirubin, Coombs test, uric acid.
Overdosage
Management of acute overdosage with carbidopa-levodopa extended-release tablet is the same as with levodopa. Pyridoxine is not effective in reversing the actions of carbidopa-levodopa extended-release tablet.
General supportive measures should be employed, along with immediate gastric lavage. Intravenous fluids should be administered judiciously and an adequate airway maintained. Electrocardiographic monitoring should be instituted and the patient carefully observed for the development of arrhythmias; if required, appropriate antiarrhythmic therapy should be given. The possibility that the patient may have taken other drugs as well as carbidopa-levodopa extended-release tablet should be taken into consideration. To date, no experience has been reported with dialysis; hence, its value in overdosage is not known.
Based on studies in which high doses of levodopa and/or carbidopa were administered, a significant proportion of rats and mice given single oral doses of levodopa of approximately 1500-2000 mg/kg are expected to die. A significant proportion of infant rats of both sexes are expected to die at a dose of 800 mg/kg. A significant proportion of rats are expected to die after treatment with similar doses of carbidopa. The addition of carbidopa in a 1:10 ratio with levodopa increases the dose at which a significant proportion of mice are expected to die to 3360 mg/kg.
Dosage And Administration
Carbidopa-levodopa extended-release tablet contains carbidopa and levodopa in a 1:4 ratio as either the 50 mg/200 mg tablet or the 25 mg/100 mg tablet. The daily dosage of carbidopa-levodopa extended-release tablet must be determined by careful titration. Patients should be monitored closely during the dose adjustment period, particularly with regard to appearance or worsening of involuntary movements, dyskinesias or nausea. Carbidopa-levodopa extended-release tablet, 50 mg/200 mg may be administered as whole or as half-tablets which should not be chewed or crushed. Carbidopa-levodopa extended-release tablet 25 mg/100 mg may be used in combination with carbidopa-levodopa extended-release tablet 50 mg/200 mg to titrate to the optimum dosage, or as an alternative to the 50 mg/200 mg half-tablet.
Standard drugs for Parkinson's disease, other than levodopa without a decarboxylase inhibitor, may be used concomitantly while carbidopa-levodopa extendedrelease tablet is being administered, although their dosage may have to be adjusted.
Since carbidopa prevents the reversal of levodopa effects caused by pyridoxine, carbidopa-levodopa extended-release tablet can be given to patients receiving supplemental pyridoxine (vitamin B6).
Initial Dosage
Patients currently treated with conventional carbidopa-levodopa preparations
Studies show that peripheral dopa-decarboxylase is saturated by the bioavailable carbidopa at doses of 70 mg a day and greater. Because the bioavailabilities of carbidopa and levodopa in carbidopa-levodopa tablets and carbidopa-levodopa extended-release tablet are different, appropriate adjustments should be made, as shown in Table II.
TABLE II Approximate Bioavailabilities at Steady State This table is only a guide to bioavailabilities since other factors such as food, drugs, and inter-patient variabilities may affect the bioavailability of carbidiopa and levodopa. Tablet Amount ofLevodopa (mg)In Each Tablet ApproximateBioavailability Approximate Amountof BioavailableLevodopa (mg) inEach Tablet  Carbidopa-LevodopaExtended-releaseTablet, 50 mg/200 mg  200  0.70-0.75 The extent of availability of levodopa from carbidopa-levodopa extended-release tablet was about 70-75% relative to intravenous levodopa or standard Carbidopa-levodopa tablets in the elderly.  140-150  Carbidopa-LevodopaTablets, 25 mg/100 mg  100  0.99 The extent of availability of levodopa from carbidopa-levodopa tablets was 99% relative to intravenous levodopa in the healthy elderly.  99
Dosage with carbidopa-levodopa extended-release tablet should be substituted at an amount that provides approximately 10% more levodopa per day, although this may need to be increased to a dosage that provides up to 30% more levodopa per day depending on clinical response (see DOSAGE AND ADMINISTRATION: Titration with carbidopa and levodopa extended-release tablet ). The interval between doses of carbidopa-levodopa extended-release tablet should be 4-8 hours during the waking day. (See CLINICAL PHARMACOLOGY: Pharmacodynamics .)
A guideline for initiation of carbidopa-levodopa extended-release tablet is shown in Table III.
Table III Guidelines for Initial Conversion from Carbidopa-Levodopa Tablets to Carbidopa-Levodopa Extended-release Tablet Carbidopa-Levodopa Tablets Carbidopa-LevodopaExtended-release Tablet Total Daily Dose For dosing ranges not shown in the table see DOSAGE AND ADMINISTRATION: Initial Dosage — Patients currently treated with conventional carbidopa-levodopa preparations . Suggested  Levodopa (mg)  Dosage Regimen  300-400  200 mg b.i.d.  500-600  300 mg b.i.d. or 200 mg t.i.d.  700-800  A total of 800 mg in 3 or more divided doses (e.g., 300 mg a.m., 300 mg early p.m., and 200 mg later p.m.)  900-1000  A total of 1000 mg in 3 or more divided doses (e.g., 400 mg a.m., 400 mg early p.m., and 200 mg later p.m.) Patients currently treated with levodopa without a decarboxylase inhibitor
Levodopa must be discontinued at least twelve hours before therapy with carbidopa-levodopa extended-release tablet is started. Carbidopa-levodopa extended-release tablet should be substituted at a dosage that will provide approximately 25% of the previous levodopa dosage. In patients with mild to moderate disease, the initial dose is usually 1 tablet of carbidopa-levodopa extended-release tablet 50 mg/200 mg b.i.d.
Patients not receiving levodopa
In patients with mild to moderate disease, the initial recommended dose is 1 tablet of carbidopa-levodopa extended-release tablet 50 mg/200 mg b.i.d. Initial dosage should not be given at intervals of less than 6 hours.
Titration with carbidopa-levodopa extended-release tablet
Following initiation of therapy, doses and dosing intervals may be increased or decreased depending upon therapeutic response. Most patients have been adequately treated with doses of carbidopa-levodopa extended-release tablet that provide 400 to 1600 mg of levodopa per day, administered as divided doses at intervals ranging from 4 to 8 hours during the waking day. Higher doses of carbidopa-levodopa extended-release tablet (2400 mg or more of levodopa per day) and shorter intervals (less than 4 hours) have been used, but are not usually recommended.
When doses of carbidopa-levodopa extended-release tablet are given at intervals of less than 4 hours, and/or if the divided doses are not equal, it is recommended that the smaller doses be given at the end of the day.
An interval of at least 3 days between dosage adjustments is recommended.
Maintenance
Because Parkinson's disease is progressive, periodic clinical evaluations are recommended; adjustment of the dosage regimen of carbidopa-levodopa extended release tablet may be required.
Addition of Other Antiparkinson Medications
Anticholinergic agents, dopamine agonists, and amantadine can be given with carbidopa-levodopa extended-release tablet. Dosage adjustment of carbidopa-levodopa extended-release tablet may be necessary when these agents are added.
A dose of carbidopa-levodopa tablets, 25 mg/100 mg or 10 mg/100 mg (one half or a whole tablet) can be added to the dosage regimen of carbidopa-levodopa extended-release tablet in selected patients with advanced disease who need additional immediate-release levodopa for a brief time during daytime hours.
Interruption of Therapy
Sporadic cases of a symptom complex resembling Neuroleptic Malignant Syndrome (NMS) have been associated with dose reductions and withdrawal of carbidopa-levodopa tablets or carbidopa-levodopa extended-release tablets.
Patients should be observed carefully if abrupt reduction or discontinuation of carbidopa-levodopa extended-release tablet is required, especially if the patient is receiving neuroleptics. (See WARNINGS .)
If general anesthesia is required, carbidopa-levodopa extended-release tablet may be continued as long as the patient is permitted to take oral medication. If therapy is interrupted temporarily, the patient should be observed for symptoms resembling NMS, and the usual dosage should be administered as soon as the patient is able to take oral medication.
How Supplied
Carbidopa-levodopa extended-release tablet, 25 mg/100 mg (carbidopa-levodopa) containing 25 mg of carbidopa and 100 mg of levodopa, are purple colored, oval, convex, compressed tablets, that are debossed with "G" on one side and coded "392" on other side. They are supplied as follows:
NDC 0115-3922-01 bottles of 100NDC 0115-3922-02 bottles of 500
Carbidopa-levodopa extended-release tablet, 50 mg/200 mg (carbidopa-levodopa) containing 50 mg of carbidopa and 200 mg of levodopa, are purple colored, oval, convex, compressed tablets, that are debossed with "G" left of bisect on one side and coded "391" on other side.
NDC 0115-3911-01 bottles of 100NDC 0115-3911-02 bottles of 500
Storage
Store at 20° to 25°C (68° to 77°F) [see USP Controlled Room Temperature].
Dispense in a tightly-closed, light-resistant container (USP).
Mfg. by:IMPAX Laboratories, Inc.Hayward, California 94544 USA
Dist. by:Global PharmaceuticalsDivision of IMPAX Laboratories, Inc.Philadelphia, PA 19124 USA
Rev. 07/2010425-02
Principal Display Panel - 100 Mg Bottle Label
NDC 0115-3922-01
Carbidopa-Levodopa
Extended-releaseTablets
25 mg/100 mg
Rx only
100 TABLETS
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Principal Display Panel - 200 Mg Bottle Label
NDC 0115-3911-01
Carbidopa-Levodopa
Extended-releaseTablets
50 mg/200 mg
Rx only
100 TABLETS
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