Carbidopa

Carbidopa tablets are indicated for use with carbidopa-levodopa or with levodopa in the treatment of the symptoms of idiopathic Parkinson’s disease (paralysis agitans), postencephalitic parkinsonism, and symptomatic parkinsonism, which may follow injury to the nervous system by carbon monoxide intoxication and/or manganese intoxication. Carbidopa tablets are for use with carbidopa-levodopa in patients for whom the dosage of carbidopa-levodopa provides less than adequate daily dosage (usually 70 mg daily) of carbidopa. Carbidopa tablets are for use with levodopa in the occasional patient whose dosage requirement of carbidopa and levodopa necessitates separate titration of each medication. …

• Whether given with carbidopa-levodopa or with levodopa, the optimal daily dose of carbidopa must be determined by careful titration
• Most patients respond to a 1:10 proportion of carbidopa and levodopa, provided the daily dosage of carbidopa is 70 mg or more a day
• The maximum daily dosage of carbidopa should not exceed 200 mg, since clinical experience with larger dosages is limited
• If the patient is taking carbidopa-levodopa, the amount of carbidopa in carbidopa-levodopa should be considered when calculating the total amount of carbidopa to be administered each day
• Patients Receiving Carbidopa-Levodopa Who Require Additional Carbidopa Some patients taking carbidopa-levodopa may not have adequate reduction in nausea and vomiting when the dosage of carbidopa is less than 70 mg a day, and the dosage of levodopa is less than 700 mg a day
• When these patients are taking carbidopa-levodopa, 25 mg of carbidopa may be given with the first dose of carbidopa-levodopa each day
• Additional doses of 12.5 mg or 25 mg may be given during the day with each dose of carbidopa-levodopa
• Carbidopa may be given with any dose carbidopa-levodopa as required for optimum therapeutic response
• The maximum daily dosage of carbidopa, given as carbidopa and as carbidopa-levodopa), should not exceed 200 mg
• Patients Requiring Individual Titration of Carbidopa and Levodopa Dosage Although carbidopa-levodopa is the most frequently used of carbidopa and levodopa administration, there may be an occasional patient who requires individually titrated doses of these two drugs. …

• Carcinogenesis, Mutagenesis, Impairment of Fertility Carcinogenesis There were no significant differences between treated and control rats with respect to mortality or neoplasia in a 96-week study of carbidopa at oral doses of 25, 45, or 135 mg/kg/day
• Combinations of carbidopa and levodopa (10 to 20, 10 to 50, 10 to 100 mg/kg/day) were given orally to rats for 106 weeks
• No effect on mortality or incidence and type of neoplasia was seen when compared to concurrent controls. …

Clinical studies of carbidopa did not include sufficient numbers of subjects aged 65 and over to determine whether they respond differently from younger subjects. Other clinical experience has not identified differences in responses between the elderly and younger patients. …

• Impulse Control/Compulsive Behaviors Postmarketing reports suggest that patients treated with anti-Parkinson medications can experience intense urges to gamble, increased sexual urges, intense urges to spend money uncontrollably, binge eating, and other intense urges
• Patients may be unable to control these urges while taking one or more of the medications that are used
• For the treatment of Parkinson’s disease and that increase central dopaminergic tone, including carbidopa taken with levodopa and carbidopa
• In some cases, although not all, these urges were reported to have stopped when the dose of anti-Parkinson medications was reduced or discontinued. …

• Carbidopa tablets are contraindicated in patients with known hypersensitivity to any component of this drug
• Nonselective monoamine oxidase (MAO) inhibitors are contraindicated for use with levodopa or carbidopa-levodopa combination products with or without carbidopa
• These inhibitors must be discontinued at least two weeks prior to initiating therapy with levodopa. …

Dyskinesia Carbidopa may potentiate the dopaminergic side effects of levodopa and may cause or exacerbate preexisting dyskinesia.

Carbidopa has no antiparkinsonian effect when given alone. It is indicated for use with carbidopa-levodopa or levodopa. Carbidopa does not decrease adverse reactions due to central effects of levodopa. When carbidopa is to be given to carbidopa-naive patients who are being treated with levodopa alone, the two drugs should be given at the same time. At least twelve hours should elapse between the last dose of levodopa and initiation of therapy with carbidopa and levodopa in combination. Start with no more than one-fifth (20%) to one-fourth (25%) of the previous daily dosage of levodopa when given without carbidopa. See the DOSAGE AND ADMINISTRATION section before initiating therapy. …

Carbidopa has not been demonstrated to have any overt pharmacodynamic actions in the recommended doses. The only adverse reactions that have been observed have been with concomitant use of carbidopa with other drugs such as levodopa, and with carbidopa-levodopa combination products. When carbidopa is administered concomitantly with levodopa or carbidopa-levodopa combination products, the most common adverse reactions have included dyskinesias such as choreiform, dystonic, and other involuntary movements, and nausea. …

It is important that carbidopa with levodopa be taken at regular intervals according to the schedule outlined by the health care provider. Caution patients not to change the prescribed dosage regimen and not to add any additional antiparkinson medications, including other carbidopa-levodopa preparations without first consulting a physician. Advise patients that sometimes a ‘wearing-off’ effect may occur at the end of the dosing interval. …

No reports of overdose with carbidopa have been received. Management of overdosage with carbidopa is the same as that with levodopa or carbidopa-levodopa preparations. In the event of overdosage, 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. …

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