Carbidopa is indicated for use in the management of the symptoms of idiopathic Parkinson's disease, postencephalitic parkinsonism, and symptomatic parkinsonism caused by carbon monoxide intoxication and/or manganese intoxication to the nervous system.

Parkinson's Disease

The optimal daily dosage of Carbidopa must be determined by careful titration, whether given with carbidopa-levodopa or with levodopa. Most patients respond to a 1:10 ratio of carbidopa and levodopa, as long as the daily dose of carbidopa is 70 mg or higher. Because clinical experience with higher dosages is limited, the maximum daily dose of carbidopa should not exceed 200 mg. When calculating the total amount of Carbidopa to be administered each day if the patient is taking carbidopa-levodopa, the amount of carbidopa in carbidopa-levodopa should be considered.

When carbidopa is administered concomitantly with levodopa or carbidopa-levodopa combination products, the most common adverse reactions are-

• dyskinesias
• paranoia
• depression
• hallucination
• suicidal activity
• convulsion

Dyskinesia

Depression

Hallucination

Suicidal Activity

• When taken alone, Carbidopa has no antiparkinsonian effect. It is intended for use in conjunction with carbidopa-levodopa or levodopa. Carbidopa has no effect on adverse reactions caused by levodopa's central effects.
• When Carbidopa is administered to carbidopa-naive patients being treated with levodopa alone, the two drugs should be administered concurrently.
• At least twelve hours should elapse between the last dose of levodopa and the start of Carbidopa and levodopa combination therapy. When given without Carbidopa, begin with no more than one-fifth (20%) to one-fourth (25%) of the previous daily dosage of levodopa (Carbidopa). 
• The combination of Carbidopa and levodopa or carbidopa-levodopa reduces the peripheral effects (nausea, vomiting) caused by levodopa decarboxylation; however, Carbidopa does not reduce the adverse reactions caused by levodopa's central effects. Because Carbidopa allows more levodopa to reach the brain and more dopamine to be formed, certain adverse central nervous system (CNS) effects, such as dyskinesias (involuntary movements), may occur at lower doses and earlier than with levodopa alone.
• Patients taking carbidopa-levodopa products alone or in combination with other dopaminergic drugs have reported falling asleep unexpectedly while performing daily activities (includes operation of motor vehicles). Some of these incidents resulted in car accidents.
• Sporadic cases of neuroleptic malignant syndrome (NMS)-like symptoms have been reported in association with dose reductions or withdrawal of certain antiparkinsonian agents such as levodopa, carbidopa-levodopa, or carbidopa-levodopa extended-release.