Overview
Levodopa/Carbidopa is a combination medication used primarily for the treatment of Parkinson's disease and parkinsonism. Levodopa is converted to dopamine in the brain to replace the deficient neurotransmitter, while carbidopa inhibits peripheral decarboxylation of levodopa, allowing more levodopa to reach the brain and reducing peripheral side effects.
Mechanism of Action
Levodopa crosses the blood-brain barrier and is converted to dopamine by aromatic L-amino acid decarboxylase in the brain, replenishing depleted dopamine levels in the basal ganglia. Carbidopa is a peripheral decarboxylase inhibitor that prevents the conversion of levodopa to dopamine outside the CNS, increasing levodopa availability in the brain and reducing peripheral adverse effects like nausea and vomiting.
Indications
- Parkinson's disease
- Parkinsonism (including post-encephalitic and arteriosclerotic parkinsonism)
- Symptomatic parkinsonism resulting from carbon monoxide or manganese intoxication
Dosage
Dosage must be individualized. Typical starting dose: Sinemet 25-100 (containing 25 mg carbidopa and 100 mg levodopa) taken 3 times daily. Maximum daily dose should not exceed 8 tablets of Sinemet 25-100 or equivalent. Adjust gradually based on response and tolerance.
Contraindications
- Hypersensitivity to any component
- Narrow-angle glaucoma
- Patients with a history of melanoma or undiagnosed skin lesions
- Concurrent use with non-selective monoamine oxidase (MAO) inhibitors (MAOIs must be discontinued at least 2 weeks prior to initiation)
- Patients with suspicious, undiagnosed skin lesions or history of melanoma
Side Effects
- Nausea
- Dyskinesias
- Orthostatic hypotension
- Hallucinations
- Confusion
- Dizziness
- Dry mouth
- Insomnia
- Anxiety
- Abnormal dreams
- Vomiting
- Anorexia
- Cardiac arrhythmias
- Darkened sweat and urine
Interactions
- MAO inhibitors (risk of hypertensive crisis)
- Dopamine D2 receptor antagonists (e.g., phenothiazines, butyrophenones, risperidone) may reduce efficacy
- Iron salts may reduce levodopa absorption
- Antihypertensive drugs may have additive hypotensive effects
- Protein-rich meals may reduce levodopa absorption
- Tricyclic antidepressants may reduce levodopa absorption and increase hypotension risk