A fixed-dose combination of the dopamine precursor Levodopa and the peripheral aromatic L-amino acid decarboxylase (AADC) inhibitor Carbidopa. It is the cornerstone of symptomatic treatment for Parkinson's disease (PD). Carbidopa prevents the peripheral conversion of Levodopa to dopamine, allowing a greater proportion of Levodopa to cross the blood-brain barrier and be converted to dopamine in the striatum, thereby enhancing central efficacy and reducing peripheral dopaminergic side effects like nausea and vomiting.
Adult: Initial: 1 tablet (100mg/10mg) three or four times daily. Titrate slowly based on response and tolerance. Usual maintenance: 4 to 8 tablets per day in divided doses (every 4-8 hours). Maximum daily dose is individual tolerance, but often limited by dyskinesias.
Note: Take on an empty stomach, 30-60 minutes before meals or 1-2 hours after meals to enhance absorption. If nausea occurs, may take with a small, low-protein snack (e.g., crackers). Do not crush or chew sustained-release formulations (if applicable). Swallow whole with water.
Levodopa is a metabolic precursor to dopamine. In Parkinson's disease, dopaminergic neurons in the substantia nigra degenerate, leading to dopamine deficiency in the striatum. Levodopa crosses the blood-brain barrier via active transport, where it is decarboxylated by central aromatic L-amino acid decarboxylase (AADC) to form dopamine, replenishing depleted striatal dopamine levels. Carbidopa, which does not cross the BBB, inhibits peripheral AADC, reducing the conversion of Levodopa to dopamine outside the CNS. This increases the bioavailability of Levodopa to the brain (by 5-10 fold) and minimizes peripheral dopaminergic side effects, allowing for lower and more effective dosing.
Pregnancy: Category C (US FDA). Animal studies show teratogenicity. Use only if potential benefit justifies potential fetal risk. Data in human pregnancy is limited.
Driving: May cause dizziness, syncope, and sudden episodes of somnolence. Patients should be cautioned against driving or operating machinery until their response is known, especially at initiation or dose change.
| Non-selective MAO Inhibitors (e.g., Phenelzine, Tranylcypromine) | Risk of severe hypertensive crisis, hyperpyrexia. | Contraindicated |
| Antipsychotics (Typical: Haloperidol; Atypical: Risperidone) | Antagonize dopaminergic effect, worsening Parkinsonism. | Major |
| Antihypertensives | Additive hypotensive effect, risk of severe orthostasis. | Moderate |
| Ferrous Sulfate (Iron) | Chelation of Levodopa, reducing its absorption and efficacy. | Moderate |
| Protein-rich foods / Dietary Amino Acids | Competes for GI absorption and BBB transport, reducing efficacy. | Moderate |
| Anticholinergics (e.g., Trihexyphenidyl) | Additive therapeutic effect but also additive side effects (confusion, dry mouth). | Moderate |
| Dopamine D2 receptor antagonists (Metoclopramide) | Worsens parkinsonian symptoms. | Major |
| Selective MAO-B Inhibitors (Selegiline, Rasagiline) | Potentiation of Levodopa effect; may require dose reduction of Levodopa to avoid dyskinesias. | Moderate |
Same composition (Levodopa (100mg) + Carbidopa (10mg)), different brands: