CARBIDOPA AND LEVODOPA

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 to creamy white, odorless or practically odorless powder, freely soluble in 3N hydrochloric acid, slightly soluble in water and in methanol, practically insoluble in alcohol, in acetone, in chloroform and in ether, with a molecular weight of 244.24. It is designated chemically as (-)-L-α­hydrazino-α-methyl-β-(3,4-dihydroxybenzene) propanoic acid monohydrate. Its empirical formula is C 10 H 14 N 2 O 4 •H 2 O, and its structural formula is: Tablet content is expressed in terms of anhydrous carbidopa, which has a molecular weight of 226.24. Levodopa, USP, an aromatic amino acid, is a white to off-white, odorless , crystalline powder, slightly soluble in water, freely soluble in 3N hydrochloric acid and insoluble in alcohol with a molecular weight of 197.19. It is designated chemically as (-)-L-α-amino-β-(3,4-dihydroxybenzene) propanoic acid. Its empirical formula is C 9 H 11 NO 4 , and its structural formula is: Carbidopa and levodopa extended-release tablets, USP are supplied as extended-release tablets containing either 25 mg of carbidopa and 100 mg of levodopa, or 50 mg of carbidopa and 200 mg of levodopa. Inactive ingredients are hydroxypropyl cellulose, magnesium stearate, and hypromellose. Carbidopa and levodopa extended-release tablets USP, 25 mg/100 mg and carbidopa and levodopa extended-release tablets USP, 50 mg/200 mg also contain FD&C Blue #2 Aluminium Lake and FD&C Red #40 Aluminium Lake. The 25 mg/100 mg tablet is supplied as an oval shaped mottled tablet that is dappled-purple in color and is debossed with “L519” on one side and plain on the other. The 50 mg/200 mg tablet is supplied as an oval shaped mottled tablet that is dappled-purple in color and is debossed with “L520” on one side and plain on the other. Carbidopa and levodopa extended-release tablets, USP are polymeric-based drug delivery system that controls the release of carbidopa and levodopa as it slowly erodes. Carbidopa and levodopa extended-release tablet 25 mg/100 mg is available to facilitate titration when 100 mg steps are required. FDA approved dissolution specifications differs from the USP dissolution specifications. Structure-Carbidopa Structure-Levodopa

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

Carbidopa and levodopa extended-release tablet contains carbidopa and levodopa in a 1:4 ratio as either the 25 mg/100 mg tablet or the 50 mg/200 mg tablet. The daily dosage of carbidopa and levodopa extended-release tablets 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 and levodopa extended-release tablets should not be chewed or crushed. Standard drugs for Parkinson’s disease, other than levodopa without a decarboxylase inhibitor, may be used concomitantly while carbidopa and levodopa extended-release tablet is being administered, although their dosage may have to be adjusted. Since carbidopa prevents the reversal of levodopa effects caused by pyridoxine, carbidopa and levodopa extended-release tablets can be given to patients receiving supplemental pyridoxine (vitamin B 6 ). 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 and levodopa tablets and carbidopa and levodopa extended-release tablets are different, appropriate adjustments should be made, as shown in Table 2. Table 2: Approximate Bioavailabilities at Steady State * Tablet Amount of Levodopa (mg) in Each Tablet Approximate Bioavailability Approximate Amount of Bioavailable Levodopa (mg) in Each Tablet Carbidopa and levodopa extended-release tablets 50 mg/200 mg 200 0.7 to 0.75 † 140 to 150 Carbidopa and levodopa tablets 25 mg/100 mg 100 0.99 ‡ 99 * This table is only a guide to bioavailabilities since other factors such as food, drugs, and inter-patient variabilities may affect the bioavailability of carbidopa and levodopa. † The extent of availability of levodopa from carbidopa and levodopa extended-release tablets was about 70 to 75% relative to intravenous levodopa or standard carbidopa and levodopa tablets in the elderly. ‡ The extent of availability of levodopa from carbidopa and levodopa tablets was 99% relative to intravenous levodopa in the healthy elderly. Dosage with carbidopa and levodopa extended-release tablets 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 tablets ). The interval between doses of carbidopa and levodopa extended-release tablets should be 4 to 8 hours during the waking day. (See CLINICAL PHARMACOLOGY, Pharmacodynamics .) A guideline for initiation of carbidopa and levodopa extended-release tablet is shown in Table 3. Table 3: Guidelines for Initial Conversion from Carbidopa and Levodopa Tablets to Carbidopa and Levodopa Extended-Release Tablets Carbidopa and Levodopa Tablets Carbidopa and Levodopa Extended-Release Tablets Total Daily Dose * Suggested Levodopa (mg) Dosage Regimen 300 to 400 200 mg b.i.d. 500 to 600 300 mg b.i.d. or 200 mg t.i.d. 700 to 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 to 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.) * For dosing ranges not shown in the table see DOSAGE AND ADMINISTRATION, Initial Dosage — Patients currently treated with conventional carbidopa levodopa preparations. Patients currently treated with levodopa without a decarboxylase inhibitor: Levodopa must be discontinued at least twelve hours before therapy with carbidopa and levodopa extended-release tablet is started. Carbidopa and levodopa extended-release tablets 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 and 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 and 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 and Levodopa Extended-Release Tablets 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 and levodopa extended-release tablets 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 and levodopa extended-release tablets (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 and levodopa extended-release tablets 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 and levodopa extended-release tablets may be required. Addition of Other Antiparkinson Medications Anticholinergic agents, dopamine agonists, and amantadine can be given with carbidopa and levodopa extended-release tablets. Dosage adjustment of carbidopa and levodopa extended-release tablets may be necessary when these agents are added. A dose of carbidopa levodopa immediate release 25 mg/100 mg or 10 mg/100 mg (one half or a whole tablet) can be added to the dosage regimen of carbidopa and levodopa extended-release tablets 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 hyperpyrexia and confusion have been associated with dose reductions and withdrawal of carbidopa and levodopa tablets or carbidopa and levodopa extended-release tablets. Patients should be observed carefully if abrupt reduction or discontinuation of carbidopa and levodopa extended-release tablet is required, especially if the patient is receiving neuroleptics. (See WARNINGS.) If general anesthesia is required, carbidopa and levodopa extended-release tablets 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.

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

In controlled clinical trials, patients predominantly with moderate to severe motor fluctuations while on carbidopa and levodopa tablets were randomized to therapy with either carbidopa and levodopa tablets or carbidopa and levodopa extended-release tablets. The adverse experience frequency profile of carbidopa and levodopa extended-release tablets did not differ substantially from that of carbidopa and levodopa, as shown in Table 1. Table 1: Clinical Adverse Experiences Occurring in 1% or Greater of Patients Carbidopa and Levodopa Extended-Release Tablets n=491 Carbidopa and Levodopa Tablets n=524 Adverse Experience % % 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 1.9 Dream abnormalities 1.8 0.8 Dystonia 1.8 0.8 Vomiting 1.8 1.9 Upper respiratory infection 1.8 1 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 Orthostatic hypotension 1 1.1 Shoulder pain 1 0.6 Chest pain 1 0.8 Muscle cramps 0.8 1 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 and levodopa extended-release tablets and 475 who received carbidopa and 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 and levodopa extended-release tablets, listed 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 postmarketing experience with carbidopa and levodopa extended-release tablets: Cardiovascular Cardiac irregularities, syncope. Gastrointestinal Taste alterations, dark saliva. Hypersensitivity Angioedema, urticaria, pruritus, bullous lesions (including pemphigus-like reactions). Nervous System/Psychiatric Increased tremor, peripheral neuropathy, psychotic episodes including delusions and paranoid ideation, pathological gambling, increased libido including hypersexuality, impulse control symptoms. 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 and levodopa extended-release tablets are: Cardiovascular Phlebitis. Gastrointestinal Gastrointestinal bleeding, development of duodenal ulcer, sialorrhea, bruxism, hiccups, flatulence, burning sensation of tongue. Hematologic Hemolytic and non-hemolytic anemia, thrombocytopenia, leukopenia, agranulocytosis. Hypersensitivity Henoch-Schönlein 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.

Caution should be exercised when the following drugs are administered concomitantly with carbidopa and levodopa extended-release tablets . 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 and levodopa extended-release tablet is started, dosage adjustment of the antihypertensive drug may be required. For patients receiving 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 D 2 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 and levodopa extended-release tablets should be carefully observed for loss of therapeutic response. Use of carbidopa and levodopa extended-release tablets with dopamine-depleting agents (e.g., reserpine and tetrabenazine) or other drugs known to deplete monoamine stores is not recommended. Carbidopa and levodopa extended-release tablets and iron salts or multivitamins containing iron salts should be coadministered with caution. Iron salts can form chelates with levodopa and carbidopa and consequently reduce the bioavailability of carbidopa and levodopa. 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.