Carbidopa and Levodopa

Carbidopa and levodopa 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. 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. 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.

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

When carbidopa and levodopa tablets are to be given to patients who are being treated with levodopa, levodopa must be discontinued at least twelve hours before therapy with the combination product is started. In order to reduce adverse reactions, it is necessary to individualize therapy. See DOSAGE AND ADMINISTRATION section before initiating therapy. The addition of carbidopa with levodopa in the form of this combination product reduces the peripheral effects (nausea, vomiting) due to decarboxylation of levodopa; however, carbidopa does not decrease the adverse reactions due to the central effects of levodopa.

Because carbidopa permits more levodopa to reach the brain and more dopamine to be formed, certain adverse central nervous system (CNS) effects, e.g., dyskinesias (involuntary movements), may occur at lower dosages and sooner with carbidopa and levodopa than with levodopa alone. All patients should be observed carefully for the development of depression with concomitant suicidal tendencies. Carbidopa and levodopa should be administered cautiously to patients with severe cardiovascular or pulmonary disease, bronchial asthma, renal, hepatic or endocrine disease.