Carbidopa

Pronunciation: (CAR-bih-doe-puh)
Class: Antiparkinson agent

Trade Names:
Lodosyn
- Tablets 25 mg

Pharmacology

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Inhibits peripheral decarboxylation of levodopa, making more levodopa available for transport to brain.

Indications and Usage

Has no effect as single agent. For use with levodopa in treatment of idiopathic Parkinson disease, postencephalitic parkinsonism and symptomatic parkinsonism associated with carbon monoxide or manganese poisoning.

Unlabeled Uses

Reduction of breakdown of L-5-hydroxytryptophan for treatment of postanoxic intention myoclonus.

Contraindications

Hypersensitivity to carbidopa or levodopa.

Dosage and Administration

Adults

PO in 1:10 ratio to levodopa (eg, 10 mg carbidopa/100 mg levodopa) 3 to 4 times daily. With regimen of 1 mg carbidopa/100 mg levodopa, additional 12.5 to 25 mg carbidopa may be administered every day or every other day with first dose if needed. With regimen of 25 mg carbidopa/250 mg levodopa, 12.5 to 25 mg carbidopa may be added by 1/ 2 to 1 tablet every day or every other day to max of 8 tablets/day (2 tablets 4 times daily) for optimal therapeutic response (max, 200 mg/day).

Initiating combination therapy

Do not give carbidopa and levodopa together until at least 8 h after last dose of levodopa was taken alone. Lower levodopa dose to 20% to 25% of previous daily dose and administer both drugs at same time.

General Advice

Administer with food to reduce GI upset.

Storage/Stability

Store in light-resistant container at room temperature.

Drug Interactions

None well documented (see Levodopa ).

Laboratory Test Interactions

May cause false-positive test result for urinary ketones when test tape is used to determine ketonuria. False-negative test results may occur with glucose-oxidase methods of testing for urinary glucose.

Adverse Reactions

Only adverse reactions seen with carbidopa have been associated with combined use of carbidopa and levodopa.

Precautions

Monitor

CNS effects

If patient experiences any CNS effects (eg, uncontrollable movements of the face, eyelids, mouth, tongue, neck, arms, hands or legs; mood or mental changes) notify health care provider.

Pregnancy

Undetermined.

Lactation

Undetermined. Do not administer to breast-feeding mothers.

Children

Safety and efficacy not established for children younger than 18 yr of age.

Elderly

May require lower doses of carbidopa/levodopa.

Dyskinesias

Dyskinesias caused by levodopa may occur sooner or at lower doses of levodopa when levodopa and carbidopa are given concomitantly than when levodopa is administered alone.

Neuroleptic malignant-like syndrome

Muscular rigidity, fever, mental changes and increased serum CPK may occur when dose of levodopa is reduced abruptly or discontinued.

Overdosage

Symptoms

Blepharospasm.

Patient Information

Remind patient to take medication with food to prevent GI upset.
Advise patient that onset of effect of first morning dose may be delayed by up to 1 h.
Inform patient it may take several wk to few mo to experience benefit from this drug.
Caution patient that this drug may interfere with results of urine tests for glucose/ketones.
Advise patient that harmless darkening of urine and sweat may occur.
Caution patient to avoid sudden position changes to prevent orthostatic hypotension.
Advise patient that this drug may cause drowsiness and to use caution while driving or performing tasks requiring mental alertness.