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Content:
Carbidopa/Levodopa: Each 10/100 tablet contains: carbidopa, 10 mg, and levodopa, 100 mg. Each 25/100 tablets contains: carbidopa, 25 mg, and levodopa, 100 mg. Each 25/250 tablet contains: carbidopa, 25 mg, and levodopa, 250 mg. Each sustained-release tablet contains: carbidopa, 50 mg, and levodopa, 200 mg.
Action/Kinetics:
Carbidopa inhibits peripheral decarboxylation of levodopa but not central decarboxylation because it does not cross the blood-brain barrier. Since peripheral decarboxylation is inhibited, this allows more levodopa to be available for transport to the brain, where it will be converted to dopamine, thus relieving the symptoms of parkinsonism. Carbidopa and levodopa are to be given together (e.g., Sinemet). However,
the dosage of levodopa must be reduced by up to 80% when combined with carbidopa. This decreases the incidence of levodopa-induced side effects.
NOTE: Pyridoxine will not reverse the action of carbidopa/levodopa.
t
1/2, carbidopa: 1-2 hr; when given with levodopa, the t
1/2 of levodopa increases from 1 hr to 2 hr (may be as high as 15 hr in some clients). About 30% carbidopa is excreted unchanged in the urine.
Uses:
All types of parkinsonism (idiopathic, postencephalitic, following injury to the nervous system due to carbon monoxide and manganese intoxication). Carbidopa alone is used in clients who require individual titration of carbidopa and levodopa.
Investigational: Postanoxic intention myoclonus.
Warning: Levodopa must be discontinued at least 8 hr before carbidopa/levodopa therapy is initiated. Also, clients taking carbidopa/levodopa must not take levodopa concomitantly, because the former is a combination of carbidopa and levodopa.
Contraindications:
History of melanoma. MAO inhibitors should be stopped 2 weeks before therapy. Lactation.
Special Concerns:
Use during pregnancy only if benefits outweigh risks. Safety and efficacy in children less than 18 years of age have not been determined. Lower doses may be necessary in geriatric clients due to aged-related decreases in peripheral dopa decarboxylase.
Side Effects:
Because more levodopa reaches the brain, dyskinesias may occur at lower doses with carbidopa/levodopa than with levodopa alone. Clients abruptly withdrawn from levodopa may experience neuroleptic malignant-like syndrome including symptoms of muscular rigidity, hyperthermia, increased serum phosphokinase, and changes in mental status.
Laboratory Test Alterations:
Creatinine, BUN, and uric acid.
Drug Interactions:
Use with tricyclic antidepressants may cause hypertension and dyskinesia.
How Supplied:
Carbodopa:
Tablet: 25 mg.
Carbidopa/Levodopa: See Content
Dosage
?Tablets
Parkinsonism, clients not receiving levodopa.
Initial: 1 tablet of 10 mg carbidopa/100 mg levodopa t.i.d.-q.i.d. or 25 mg carbidopa/100 mg levodopa t.i.d.;
then, increase by 1 tablet q 1-2 days until a total of 8 tablets/day is taken. If additional levodopa is required, substitute 1 tablet of 25 mg carbidopa/250 mg levodopa t.i.d.-q.i.d.
Parkinsonism, clients receiving levodopa.
Initial: Carbidopa/levodopa dosage should be about 25% of prior levodopa dosage (levodopa dosage is discontinued 8 hr before carbidopa/levodopa is initiated);
then, adjust dosage as required. Suggested starting dose is 1 tablet of 25 mg carbidopa/250 mg levodopa t.i.d.-q.i.d. for clients taking more than 1500 mg levodopa or 25 mg carbidopa/100 mg levodopa for clients taking less than 1500 mg levodopa.
?Sustained-Release Tablets
Parkinsonism, clients not receiving levodopa.
1 tablet b.i.d. at intervals of not less than 6 hr. Depending on the response, dosage may be increased or decreased. Usual dose is 2-8 tablets/day in divided doses at intervals of 4-8 hr during waking hours (if divided doses are not equal, the smaller dose should be given at the end of the day).
Parkinsonism, clients receiving levodopa.
1 tablet b.i.d. Carbidopa is available alone for clients requiring additional carbidopa (i.e., inadequate reduction in N&V;); in such clients, carbidopa may be given at a dose of 25 mg with the first daily dose of carbidopa/levodopa. If necessary, additional carbidopa, at doses of 12.5 or 25 mg, may be given with each dose of carbidopa/levodopa.
Clients receiving carbidopa/levodopa who require additional carbidopa.
In clients taking 10 mg carbidopa/100 mg levodopa, 25 mg carbidopa may be given with the first dose each day. Additional doses of 12.5 or 25 mg may be given during the day with each dose. If the client is taking 25 mg carbidopa/250 mg levodopa, a dose of 25 mg carbidopa may be given with any dose, as needed. The maximum daily dose of carbidopa is 200 mg.
