Carbidopa and Levodopa: Package Insert and Label Information

CARBIDOPA AND LEVODOPA- carbidopa and levodopa tablet, extended release
Mylan Pharmaceuticals Inc.

Carbidopa and levodopa extended-release tablets, USP are an extended-release combination of carbidopa and levodopa for the treatment of Parkinson’s disease and syndrome.

Carbidopa, USP, an inhibitor of aromatic amino acid decarboxylation, is a white, crystalline compound, slightly soluble in water, with a molecular weight of 244.25. It is designated chemically as (-)-L-α-Hydrazino-3,4-dihydroxy-α-methylhydrocinnamic acid monohydrate. Its molecular formula is C₁₀ H₁₄ N₂ O₄ •H₂ O and its structural formula is:

Tablet content is expressed in terms of anhydrous carbidopa, which has a molecular weight of 226.23.

Levodopa, USP, an aromatic amino acid, is a white, crystalline compound, slightly soluble in water, with a molecular weight of 197.19. It is designated chemically as (-)-3-(3,4-Dihydroxyphenyl)-L-alanine. Its molecular formula is C₉ H₁₁ NO₄ and its structural formula is:

Each extended-release tablet, for oral administration, contains either 25 mg of carbidopa and 100 mg of levodopa or 50 mg of carbidopa and 200 mg of levodopa. In addition, each tablet contains the following inactive ingredients: FD&C Blue No. 2 Aluminum Lake, FD&C Red No. 40 Aluminum Lake, hydroxypropyl cellulose, hypromellose, and magnesium stearate.

The 25 mg/100 mg tablets are purple, oval, unscored tablets debossed with MYLAN on one side of the tablet and 88 on the other side of the tablet. The 50 mg/200 mg tablets are purple, oval, scored tablets debossed with MYLAN on one side of the tablet and 9 to the left of the score and 4 to the right of the score on the other side of the tablet. Carbidopa and levodopa extended-release tablets are designed in a drug delivery system that controls the release of carbidopa and levodopa as the tablets slowly erode. The 25 mg/100 mg carbidopa and levodopa extended-release tablet is available to facilitate titration and as an alternative to the half-tablet of 50 mg/200 mg carbidopa and levodopa extended-release.

FDA approved dissolution test specifications differ from USP.

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 and levodopa extended-release tablets contain either 25 mg of carbidopa and 100 mg of levodopa, or 50 mg of carbidopa and 200 mg of levodopa in a sustained-release dosage form designed to release these ingredients over a 4- to 6-hour period. With carbidopa and levodopa extended-release there is less variation in plasma levodopa levels than with carbidopa and levodopa immediate-release, the conventional formulation. However, carbidopa and levodopa extended-release is less systemically bioavailable than carbidopa and levodopa immediate-release and may require increased daily doses to achieve the same level of symptomatic relief as provided by carbidopa and levodopa immediate-release.

In clinical trials, patients with moderate to severe motor fluctuations who received carbidopa and levodopa extended-release did not experience quantitatively significant reductions in ‘off’ time when compared to carbidopa and levodopa immediate-release. However, global ratings of improvement as assessed by both patient and physician were better during therapy with carbidopa and levodopa extended-release than with carbidopa and levodopa immediate-release. In patients without motor fluctuations, carbidopa and levodopa extended-release, under controlled conditions, provided the same therapeutic benefit with less frequent dosing when compared to carbidopa and levodopa immediate-release.

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 and levodopa extended-release, 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 50 mg/200 mg carbidopa and levodopa extended-release was about 2 hours as compared to 0.5 hours after standard carbidopa and levodopa immediate-release. The maximum concentration of levodopa after a single dose of carbidopa and levodopa extended-release was about 35% of the standard carbidopa and levodopa immediate-release (1151 vs. 3256 ng/mL). The extent of availability of levodopa from carbidopa and levodopa extended-release was about 70-75% relative to intravenous levodopa or standard carbidopa and levodopa immediate-release in the elderly. The absolute bioavailability of levodopa from carbidopa and levodopa extended-release (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 50 mg/200 mg carbidopa and levodopa extended-release. 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 and levodopa immediate-release (163 vs. 74 ng/mL).

In these studies, using similar total daily doses of levodopa, plasma levodopa concentrations with carbidopa and levodopa extended-release fluctuated in a narrower range than with carbidopa and levodopa immediate-release. Because the bioavailability of levodopa from carbidopa and levodopa extended-release relative to carbidopa and levodopa immediate-release 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 50 mg/200 mg carbidopa and levodopa extended-release increased by about 50% and 25%, respectively, when administered with food.

At steady state, the bioavailability of carbidopa from carbidopa and levodopa immediate-release tablets is approximately 99% relative to the concomitant administration of carbidopa and levodopa. At steady state, carbidopa bioavailability from 50 mg/200 mg carbidopa and levodopa extended-release is approximately 58% relative to that from carbidopa and levodopa immediate-release.

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.

Special Populations

Geriatric

A study in eight young healthy subjects (21-22 yr) and eight elderly healthy subjects (69-76 yr) showed that the absolute bioavailability of levodopa was similar between young and elderly subjects following oral administration of levodopa and carbidopa. However, the systemic exposure (AUC) of levodopa was increased by 55% in elderly subjects compared to young subjects. Based on another study in forty patients with Parkinson’s disease, there was a correlation between age of patients and the increase of AUC of levodopa following administration of levodopa and an inhibitor of peripheral dopa decarboxylase. AUC of levodopa was increased by 28% in elderly patients (≥ 65 yr) compared to young patients (< 65 yr). Additionally, mean value of C_max for levodopa was increased by 24% in elderly patients (≥ 65 yr) compared to young patients (< 65 yr) (see PRECAUTIONS: Geriatric Use).

The AUC of carbidopa was increased in elderly subjects (n = 10, 65-76 yr) by 29% compared to young subjects (n = 24, 23-64 yr) following IV administration of 50 mg levodopa with carbidopa (50 mg). This increase is not considered a clinically significant impact.

INDICATIONS AND USAGE

Carbidopa and levodopa extended-release tablets are indicated in the treatment of Parkinson’s disease, post-encephalitic parkinsonism, and symptomatic parkinsonism that may follow carbon monoxide intoxication or manganese intoxication.

CONTRAINDICATIONS

Nonselective monoamine oxidase (MAO) inhibitors are contraindicated for use with carbidopa and levodopa extended-release tablets. These inhibitors must be discontinued at least two weeks prior to initiating therapy with carbidopa and levodopa extended-release. Carbidopa and levodopa extended-release may be administered concomitantly with the manufacturer’s recommended dose of an MAO inhibitor with selectivity for MAO type B (e.g., selegiline HCl) (see PRECAUTIONS: Drug Interactions).

Carbidopa and levodopa extended-release is contraindicated in patients with known hypersensitivity to any component of this drug and in patients with narrow-angle glaucoma.

WARNINGS

When patients are receiving levodopa without a decarboxylase inhibitor, levodopa must be discontinued at least twelve hours before carbidopa and levodopa extended-release is started. In order to reduce adverse reactions, it is necessary to individualize therapy. See DOSAGE AND ADMINISTRATION section before initiating therapy.

Carbidopa and levodopa extended-release 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 central nervous system (CNS) effects, e.g., dyskinesias, will occur at lower dosages and sooner during therapy with carbidopa and levodopa extended-release than with levodopa alone.

Patients receiving carbidopa and levodopa extended-release may develop increased dyskinesias compared to carbidopa and levodopa immediate-release. Dyskinesias are a common side effect of carbidopa-levodopa treatment. The occurrence of dyskinesias may require dosage reduction.

All patients should be observed carefully for the development of depression with concomitant suicidal tendencies.

Carbidopa and levodopa extended-release 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 and levodopa extended-release 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 and levodopa extended-release may increase the possibility of upper gastrointestinal hemorrhage in patients with a history of peptic ulcer.

Falling Asleep During Activities of Daily Living and Somnolence

Patients taking carbidopa and levodopa extended-release alone or with other dopaminergic drugs have reported suddenly falling asleep without prior warning of sleepiness while engaged in activities of daily living (includes operation of motor vehicles). Road traffic accidents attributed to sudden sleep onset have been reported. Although many patients reported somnolence while on dopaminergic medications, there have been reports of road traffic accidents attributed to sudden onset of sleep in which the patient did not perceive any warning signs, such as excessive drowsiness, and believed that they were alert immediately prior to the event. Sudden onset of sleep has been reported to occur as long as one year after the initiation of treatment.

Falling asleep while engaged in activities of daily living usually occurs in patients experiencing preexisting somnolence, although some patients may not give such a history. For this reason, prescribers should reassess patients for drowsiness or sleepiness especially since some of the events occur well after the start of treatment. Prescribers should be aware that patients may not acknowledge drowsiness or sleepiness until directly questioned about drowsiness or sleepiness during specific activities. Patients should be advised to exercise caution while driving or operating machines during treatment with carbidopa and levodopa extended-release. Patients who have already experienced somnolence or an episode of sudden sleep onset should not participate in these activities during treatment with carbidopa and levodopa extended-release.

Before initiating treatment with carbidopa and levodopa extended-release, advise patients about the potential to develop drowsiness and ask specifically about factors that may increase the risk for somnolence with carbidopa and levodopa extended-release such as the use of concomitant sedating medications and the presence of sleep disorders. Consider discontinuing carbidopa and levodopa extended-release in patients who report significant daytime sleepiness or episodes of falling asleep during activities that require active participation (e.g., conversations, eating, etc.). If treatment with carbidopa and levodopa extended-release continues, patients should be advised not to drive and to avoid other potentially dangerous activities that might result in harm if the patients become somnolent. There is insufficient information to establish that dose reduction will eliminate episodes of falling asleep while engaged in activities of daily living.

Hyperpyrexia and Confusion

Sporadic cases of a symptom complex resembling neuroleptic malignant syndrome (NMS) have been reported in association with dose reductions or withdrawal of certain antiparkinsonian agents such as levodopa, carbidopa-levodopa and carbidopa and levodopa extended-release. Therefore, patients should be observed carefully when the dosage of levodopa 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.