Carbidopa / Levodopa

Trade names

• Sinemet

Actions

• Carbidopa inhibits DOPA decarboxylase, preventing conversion of levodopa to dopamine in peripheral tissues.
• Levodopa (L-DOPA) is the precursor to the neurotransmitters dopamine, norepinephrine and epinephrine.

Route of Administration

Oral

Bioavailability

Carbidopa: 40-70%

Levodopa: 30%

Plasma protein binding

Carbidopa: 40-70%

Levodopa: 10-30%

Half-life

Carbidopa: 2 hours

Levodopa: 0.75–1.5 hours

Metabolism

Carbidopa: Not significantly metabolized

Levodopa: Decarboxylation in peripheral tissues and CNS

Elimination

Carbidopa: Renal

Levodopa: ~30% of the dose is excreted in urine unchanged

Important side-effects

Hypotension

Arrhythmias

Nausea, vomiting

Disorientation, confusion, delirium, hallucinations, delusions, psychosis

Dyskinesias

Excessive libido

Vivid dreams or insomnia

Somnolence

Recommended dose

A usual starting dose for patients in the early stages of Parkinson’s disease is 50-100 mg Levodopa 1-2 times per day.

Renal impairment

Should be administered with caution in patients with severe renal failure.

Hepatic impairment

Should be administered with caution in patients with severe impairment of hepatic function.