1. Clinical Overview
A triple combination therapy for Parkinson's disease, providing enhanced and sustained dopaminergic stimulation. Levodopa is a dopamine precursor, Carbidopa is a peripheral DOPA decarboxylase inhibitor that reduces peripheral conversion of levodopa, and Entacapone is a catechol-O-methyltransferase (COMT) inhibitor that prolongs the effect of levodopa by reducing its peripheral metabolism. This combination significantly reduces 'off' time and improves motor fluctuations in patients with advanced Parkinson's disease.
| Onset | Duration | Bioavailability |
|---|---|---|
| 30-60 minutes | 4-6 hours | Levodopa: ~30% (highly variable, increased with food); Carbidopa: 40-70%; Entacapone: 35% |
2. Mechanism of Action
This combination addresses the dopamine deficiency in the nigrostriatal pathway of Parkinson's disease through a multi-pronged approach. Levodopa, a dopamine precursor, crosses the blood-brain barrier and is converted to dopamine in the brain. Carbidopa, a peripheral aromatic L-amino acid decarboxylase (AADC) inhibitor, prevents the peripheral conversion of levodopa to dopamine, allowing more levodopa to reach the CNS and reducing peripheral side effects like nausea. Entacapone, a reversible, peripherally-acting catechol-O-methyltransferase (COMT) inhibitor, blocks the major peripheral metabolic pathway of levodopa (to 3-O-methyldopa), increasing its bioavailability and plasma half-life, leading to more sustained and stable plasma levels.
3. Indications & Uses
- Idiopathic Parkinson's Disease
- Post-encephalitic Parkinsonism
- Symptomatic Parkinsonism
4. Dosage & Administration
Adult Dosage: Individualized. Typically 1 tablet (Levodopa 100mg/Carbidopa 25mg/Entacapone 200mg) 3 to 8 times daily. Maximum daily dose of Entacapone is 1600mg (8 tablets). Dose adjustments of levodopa/carbidopa may be needed when adding entacapone; a 20-30% reduction in levodopa dose is often recommended.
Administration: Administer with or without food, but consistency is key. High-protein meals can impair absorption. Tablets should be swallowed whole with water. Do not crush or chew. Doses should be spaced approximately 3-6 hours apart while awake. The interval between the last dose of the day and the first dose the next morning should not exceed 8 hours.
5. Side Effects
Common side effects may include:
- Dyskinesia (involuntary movements)
- Nausea
- Dizziness
- Orthostatic hypotension
- Dark discoloration of urine and sweat (harmless)
- Diarrhea
- Abdominal pain
- Dry mouth
6. Drug Interactions
| Drug | Effect | Severity |
|---|---|---|
| Non-selective MAO Inhibitors (Phenelzine, Tranylcypromine) | Risk of hypertensive crisis | Contraindicated |
| Selective MAO-B Inhibitors (Selegiline, Rasagiline) | Enhanced dopaminergic effects, increased risk of dyskinesia and orthostasis. Dose adjustment may be needed. | Major |
| Iron Salts (Ferrous Sulfate) | Reduced bioavailability of levodopa/carbidopa due to chelation | Moderate |
| Antipsychotics (Typical & Atypical e.g., Haloperidol, Risperidone) | Antagonize dopaminergic effect, worsening Parkinsonism | Major |
| Antihypertensives | Additive hypotensive effect | Moderate |
| Isoniazid | May antagonize therapeutic effect of levodopa | Moderate |
| Metoclopramide | Antagonizes dopaminergic effect in CNS | Major |
| Drugs that interfere with catecholamine metabolism (e.g., Epinephrine, Norepinephrine) | Increased risk of arrhythmias and hypertension | Moderate |
| Warfarin | Entacapone may potentiate anticoagulant effect; monitor INR. | Moderate |
7. Patient Counselling
- DO take the medicine exactly as prescribed, at consistent times.
- DO inform your doctor about all other medicines, including OTC and supplements.
- DO maintain a consistent diet with regards to protein intake (avoid high-protein meals at dose times).
- DO rise slowly from sitting/lying position to avoid dizziness.
- DO report any new skin lesions or moles to your doctor.
- DON'T stop the medicine suddenly.
- DON'T crush or chew the tablets.
- DON'T drive or operate heavy machinery if you feel drowsy or have sudden sleep attacks.
- DON'T take iron supplements within 2-3 hours of this medicine.
8. Toxicology & Storage
Overdose: Exaggeration of adverse effects: Severe dyskinesias, confusion, agitation, hallucinations, tachycardia, arrhythmias, hypotension or hypertension, nausea, vomiting, GI bleeding. Priapism has been reported.
Storage: Store below 30°C. Protect from light and moisture. Keep in the original blister pack or container. Keep out of reach of children.