Carbidopa and Levodopa

INDICATIONS AND USAGE Carbidopa and levodopa 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 allows patients treated for Parkinson's disease to use much lower doses of levodopa. Some patients who responded poorly to levodopa have improved on carbidopa and levodopa tablets, USP. This is most likely due to decreased peripheral decarboxylation of levodopa caused by administration of carbidopa rather than by a primary effect of carbidopa on the nervous system. Carbidopa has not been shown to enhance the intrinsic efficacy of levodopa. Carbidopa may also reduce nausea and vomiting and permit more rapid titration of levodopa.

DOSAGE AND ADMINISTRATION The optimum daily dosage of carbidopa and levodopa tablets must be determined by careful titration in each patient. Carbidopa and levodopa tablets are available in a 1:4 ratio of carbidopa to levodopa (carbidopa and levodopa tablets 25 mg/100 mg) as well as 1:10 ratio (carbidopa and levodopa tablets 25 mg/250 mg and carbidopa and levodopa tablets 10 mg/100 mg). Tablets of the two ratios may be given separately or combined as needed to provide the optimum dosage. Studies show that peripheral dopa decarboxylase is saturated by carbidopa at approximately 70 mg to 100 mg a day. Patients receiving less than this amount of carbidopa are more likely to experience nausea and vomiting. Management of Vitamin B 6 Levels Evaluate vitamin B 6 levels prior to initiating carbidopa/levodopa therapies, including carbidopa and levodopa tablets, periodically during treatment, and as clinically indicated (See WARNINGS , Vitamin B6 Deficiency and Seizures ). If vitamin B 6 levels are low, supplement to sufficient levels per standard of care. Patients may initiate and continue treatment with carbidopa and levodopa tablets while supplementing vitamin B 6 . Usual Initial Dosage Dosage is best initiated with one tablet of carbidopa and levodopa tablets 25 mg/100 mg three times a day. This dosage schedule provides 75 mg of carbidopa per day. Dosage may be increased by one tablet every day or every other day, as necessary, until a dosage of eight tablets of carbidopa and levodopa tablets 25 mg/100 mg a day is reached. If carbidopa and levodopa tablets 10 mg/100 mg are used, dosage may be initiated with one tablet three or four times a day. However, this will not provide an adequate amount of carbidopa for many patients. Dosage may be increased by one tablet every day or every other day until a total of eight tablets (2 tablets q.i.d.) is reached. How to Transfer Patients from Levodopa Levodopa must be discontinued at least twelve hours before starting carbidopa and levodopa tablets. A daily dosage of carbidopa and levodopa tablets should be chosen that will provide approximately 25% of the previous levodopa dosage. Patients who are taking less than 1,500 mg of levodopa a day should be started on one tablet of carbidopa and levodopa tablets 25 mg/100 mg three or four times a day. The suggested starting dosage for most patients taking more than 1,500 mg of levodopa is one tablet of carbidopa and levodopa tablets 25 mg/250 mg three or four times a day. Maintenance Therapy should be individualized and adjusted according to the desired therapeutic response. At least 70 mg to 100 mg of carbidopa per day should be provided. When a greater proportion of carbidopa is required, one tablet of carbidopa and levodopa tablets 25 mg/100 mg may be substituted for each tablet of carbidopa and levodopa tablets 10 mg/100 mg. When more levodopa is required, carbidopa and levodopa tablets 25 mg/250 mg should be substituted for carbidopa and levodopa tablets 25 mg/100 mg or carbidopa and levodopa tablets 10 mg/100 mg. If necessary, the dosage of carbidopa and levodopa tablets 25 mg/250 mg may be increased by one-half or one tablet every day or every other day to a maximum of eight tablets a day. Experience with total daily dosages of carbidopa greater than 200 mg is limited. Because both therapeutic and adverse responses occur more rapidly with carbidopa and levodopa tablets than with levodopa alone, patients should be monitored closely during the dose adjustment period. Specifically, involuntary movements will occur more rapidly with carbidopa and levodopa tablets than with levodopa. The occurrence of involuntary movements may require dosage reduction. Blepharospasm may be a useful early sign of excess dosage in some patients. Addition of Other Antiparkinsonian Medications Standard drugs for Parkinson's disease, other than levodopa without a decarboxylase inhibitor, may be used concomitantly while carbidopa and levodopa tablets are being administer …

CONTRAINDICATIONS Nonselective monoamine oxidase (MAO) inhibitors are contraindicated for use with carbidopa and levodopa tablets. These inhibitors must be discontinued at least two weeks prior to initiating therapy with carbidopa and levodopa tablets. Carbidopa and levodopa 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 tablets are contraindicated in patients with known hypersensitivity to any component of this drug, and in patients with narrow-angle glaucoma.

ADVERSE REACTIONS The most common adverse reactions reported with carbidopa and levodopa tablets have included dyskinesias, such as choreiform, dystonic, and other involuntary movements, and nausea. The following other adverse reactions have been reported with carbidopa and levodopa tablets: Body as a Whole: chest pain, asthenia. Cardiovascular: cardiac irregularities, hypotension, orthostatic effects including orthostatic hypotension, hypertension, syncope, phlebitis, palpitation. Gastrointestinal: dark saliva, gastrointestinal bleeding, development of duodenal ulcer, anorexia, vomiting, diarrhea, constipation, dyspepsia, dry mouth, taste alterations. Hematologic: agranulocytosis, hemolytic and non-hemolytic anemia, thrombocytopenia, leukopenia. Hypersensitivity: angioedema, urticaria, pruritus, Henoch-Schönlein purpura, bullous lesions (including pemphigus-like reactions). Musculoskeletal: back pain, shoulder pain, muscle cramps. Nervous System/Psychiatric: psychotic episodes including delusions, hallucinations, and paranoid ideation, bradykinetic episodes ("on-off" phenomenon), confusion, agitation, dizziness, somnolence, dream abnormalities including nightmares, insomnia, paresthesia, headache, depression with or without development of suicidal tendencies, dementia, pathological gambling, increased libido including hypersexuality, impulse control symptoms. Convulsions also have occurred; however, a causal relationship with carbidopa and levodopa tablets has not been established. Respiratory: dyspnea, upper respiratory infection. Skin: rash, increased sweating, alopecia, dark sweat. Urogenital: urinary tract infection, urinary frequency, dark urine. Laboratory Tests: decreased hemoglobin and hematocrit; abnormalities in alkaline phosphatase, SGOT (AST), SGPT (ALT), LDH, bilirubin, BUN, Coombs test; elevated serum glucose; white blood cells, bacteria, and blood in the urine. Other adverse reactions that have been reported with levodopa alone and with various carbidopa and levodopa formulations, and may occur with carbidopa and levodopa tablets are: Body as a Whole: abdominal pain and distress, fatigue. Cardiovascular: myocardial infarction. Gastrointestinal: gastrointestinal pain, dysphagia, sialorrhea, flatulence, bruxism, burning sensation of the tongue, heartburn, hiccups. Metabolic: edema, weight gain, weight loss. Musculoskeletal: leg pain. Nervous System/Psychiatric: ataxia, extrapyramidal disorder, falling, anxiety, gait abnormalities, nervousness, decreased mental acuity, memory impairment, disorientation, euphoria, blepharospasm (which may be taken as an early sign of excess dosage; consideration of dosage reduction may be made at this time), trismus, increased tremor, numbness, muscle twitching, activation of latent Horner's syndrome, peripheral neuropathy. Respiratory: pharyngeal pain, cough. Skin: malignant melanoma (see also CONTRAINDICATIONS ), flushing. Special Senses: oculogyric crises, diplopia, blurred vision, dilated pupils. Urogenital: urinary retention, urinary incontinence, priapism. Miscellaneous: bizarre breathing patterns, faintness, hoarseness, malaise, hot flashes, sense of stimulation. Laboratory Tests: decreased white blood cell count and serum potassium; increased serum creatinine and uric acid; protein and glucose in urine.

The most common adverse reactions reported with carbidopa and levodopa tablets have included dyskinesias, such as choreiform, dystonic, and other involuntary movements, and nausea. The following other adverse reactions have been reported with carbidopa and levodopa tablets: Body as a Whole: chest pain, asthenia. Cardiovascular: cardiac irregularities, hypotension, orthostatic effects including orthostatic hypotension, hypertension, syncope, phlebitis, palpitation. Gastrointestinal: dark saliva, gastrointestinal bleeding, development of duodenal ulcer, anorexia, vomiting, diarrhea, constipation, dyspepsia, dry mouth, taste alterations. Hematologic: agranulocytosis, hemolytic …

Drug Interactions Caution should be exercised when the following drugs are administered concomitantly with carbidopa and levodopa tablets. Symptomatic postural hypotension occurred when carbidopa and levodopa tablets was added to the treatment of a patient receiving antihypertensive drugs. Therefore, when therapy with carbidopa and levodopa tablets 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 and levodopa may be associated with severe orthostatic hypotension not attributable to carbidopa and 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 and levodopa tablets. 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 tablets should be carefully observed for loss of therapeutic response. Use of carbidopa and levodopa tablets with dopamine-depleting agents (e.g., reserpine and tetrabenazine) or other drugs known to deplete monoamine stores is not recommended. Carbidopa and levodopa 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.

Special Populations Geriatric: A study in eight young healthy subjects (21 yr to 22 yr) and eight elderly healthy subjects (69 yr to 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 yr to 76 yr) by 29% compared to young subjects (n=24, 23 yr to 64 yr) following IV administration of 50 mg levodopa with carbidopa (50 mg). This increase is not considered a clinically significant impact.

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.

DESCRIPTION Carbidopa and levodopa tablets, USP are a 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 powder, freely soluble in 3N hydrochloric acid, slightly soluble in water and methanol, practically insoluble in alcohol, acetone, ether and chloroform, with a molecular weight of 244.3. It is designated chemically as (—)-L-α-hydrazino-α-methyl-β-(3,4-dihydroxybenzene) propanoic acid monohydrate. Its molecular 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 226.3. Levodopa USP, an aromatic amino acid, is a white to off-white, crystalline powder, slightly soluble in water, freely soluble in 3N hydrochloric acid, insoluble in alcohol, with a molecular weight of 197.2. It is designated chemically as (—)-L-α-amino-β-(3,4-dihydroxybenzene) propanoic acid. Its molecular formula is C 9 H 11 NO 4 , and its structural formula is: Carbidopa and levodopa is supplied as tablets for oral administration in three strengths: Carbidopa and levodopa tablets USP, 25 mg/100 mg containing 25 mg of carbidopa USP and 100 mg of levodopa USP. Carbidopa and levodopa tablets USP, 10 mg/100 mg containing 10 mg of carbidopa USP and 100 mg of levodopa USP. Carbidopa and levodopa tablets USP, 25 mg/250 mg containing 25 mg of carbidopa USP and 250 mg of levodopa USP. Inactive ingredients are crospovidone, hydroxypropyl cellulose, magnesium stearate, microcrystalline cellulose, and pregelatinized starch (maize). Carbidopa and levodopa tablets USP, 10 mg/100 mg and 25 mg/250 mg also contain FD&C Blue No.2 Aluminum Lake. Carbidopa and levodopa tablets USP, 25 mg/100 mg also contain D&C Yellow No.10. FDA approved dissolution test specifications differ from USP. chemical structure 1 chemical structure 2

OVERDOSAGE Management of acute overdosage with carbidopa and levodopa tablets is the same as management of acute overdosage with levodopa. Pyridoxine is not effective in reversing the actions of carbidopa and levodopa tablets. 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 and levodopa tablets 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 1,500 mg/kg to 2,000 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 3,360 mg/kg.

HOW SUPPLIED Carbidopa and levodopa tablets, USP 25 mg/100 mg are mottled (orange colored speckles) yellow to light yellow colored oval shaped, biconvex, uncoated tablets debossed with "518" on one side and plain on the other side. They are supplied as follows: Bottle of 30 with child-resistant closure, NDC 62756-518-83 Bottle of 100 with child-resistant closure, NDC 62756-518-88 Bottle of 100, NDC 62756-518-08 Bottle of 500, NDC 62756-518-13 Bottle of 1000, NDC 62756-518-18 Carbidopa and levodopa tablets, USP 10 mg/100 mg are mottled blue to light blue colored oval shaped, biconvex, uncoated tablets debossed with "517" on one side and plain on the other side. They are supplied as follows: Bottle of 30 with child-resistant closure, NDC 62756-517-83 Bottle of 100 with child-resistant closure, NDC 62756-517-88 Bottle of 100, NDC 62756-517-08 Bottle of 500, NDC 62756-517-13 Bottle of 1000, NDC 62756-517-18 Carbidopa and levodopa tablets, USP 25 mg/250 mg are mottled blue to light blue colored oval shaped, biconvex, uncoated tablets debossed with "519" on one side and plain on the other side. They are supplied as follows: Bottle of 30 with child-resistant closure, NDC 62756-519-83 Bottle of 100 with child-resistant closure, NDC 62756-519-88 Bottle of 100, NDC 62756-519-08 Bottle of 500, NDC 62756-519-13 Bottle of 1000, NDC 62756-519-18 Carbidopa and levodopa tablets, USP 25 mg/250 mg are mottled blue to light blue colored round shaped, biconvex, uncoated tablets debossed with "519" on one side and plain on the other side. They are supplied as follows: Bottle of 100 with child-resistant closure, NDC 62756-985-01 Bottle of 500, NDC 62756-985-02 Storage Store at 20° to 25°C (68° to 77°F) [see USP Controlled Room Temperature]. Store in a tightly closed container, protected from light and moisture. Dispense in a tightly closed, light-resistant container.