1. Clinical Overview
Oxcarbazepine is a second-generation antiepileptic drug (AED) and a keto-analogue of carbamazepine. It is a prodrug primarily metabolized to its active metabolite, 10-monohydroxy derivative (MHD). It is widely used in the Indian market for the management of partial seizures with or without secondary generalization in adults and children. It offers a favorable side effect profile and fewer drug interactions compared to carbamazepine.
| Onset | Duration | Bioavailability |
|---|---|---|
| Steady-state concentrations of the active metabolite (MHD) are typically reached within 2-3 days of starting therapy. | The therapeutic effect is maintained with twice-daily dosing due to the half-life of the active metabolite (MHD). | Greater than 95% for the parent drug. The active metabolite (MHD) also exhibits high bioavailability. |
2. Mechanism of Action
The primary mechanism of action is blockade of voltage-sensitive sodium channels, leading to stabilization of hyperexcited neuronal membranes, inhibition of repetitive neuronal firing, and diminution of propagation of synaptic impulses.
3. Indications & Uses
- Monotherapy or adjunctive therapy in the treatment of partial seizures with or without secondary generalized tonic-clonic seizures in adults.
- Monotherapy or adjunctive therapy in the treatment of partial seizures with or without secondary generalized tonic-clonic seizures in children aged 6 years and above.
4. Dosage & Administration
Adult Dosage: **Initiation (Adjunctive Therapy):** 600 mg/day in two divided doses (300 mg BID). May be increased by 600 mg/day at weekly intervals. Recommended dose range: 600-2400 mg/day. **Initiation (Monotherapy):** 600 mg/day in two divided doses, increased by 300 mg/day every third day to a dose of 1200 mg/day. Further titration based on response.
Administration: May be taken with or without food. Tablets should be swallowed whole with water. Do not crush or chew. The total daily dose should be administered in two equally divided doses (BID) to minimize peak-dose side effects.
5. Side Effects
Common side effects may include:
- Dizziness (22-49%)
- Somnolence (20-36%)
- Headache (13-32%)
- Diplopia (double vision) (14-40%)
- Nausea (15-29%)
- Vomiting (13-36%)
- Fatigue (12-21%)
- Ataxia (5-31%)
6. Drug Interactions
| Drug | Effect | Severity |
|---|---|---|
| Phenytoin | Oxcarbazepine decreases phenytoin levels by ~30-40%. Phenytoin decreases MHD levels by ~30%. | Major |
| Carbamazepine | Decreases MHD levels by ~30-40%. | Major |
| Valproic Acid | May decrease MHD levels slightly. Oxcarbazepine may decrease valproate levels. | Moderate |
| Phenobarbital | Decreases MHD levels by ~25%. | Moderate |
| Oral Contraceptives (Ethinyl Estradiol, Levonorgestrel) | Oxcarbazepine induces CYP3A4, reducing contraceptive hormone levels by up to 50%, increasing risk of contraceptive failure. | Major |
| Warfarin | May decrease warfarin efficacy via enzyme induction. Monitor INR closely. | Major |
| Felodipine | Oxcarbazepine may decrease felodipine levels, reducing antihypertensive effect. | Moderate |
| Verapamil | Verapamil may decrease MHD levels. | Moderate |
| Lithium | Increased risk of neurotoxicity (ataxia, tremor, nystagmus). | Moderate |
7. Patient Counselling
- DO take the medicine exactly as prescribed, at the same times each day.
- DO NOT stop taking the medicine suddenly; it can cause increased seizures.
- DO inform all your doctors and dentists you are taking oxcarbazepine.
- DO NOT drive or operate heavy machinery until you know how the medicine affects you.
- DO use effective non-hormonal or high-dose hormonal contraception (after consulting your doctor) as it can make regular birth control pills less effective.
- DO NOT start any new medicine (including OTC, herbal) without consulting your doctor.
8. Toxicology & Storage
Overdose: Symptoms are primarily dose-related CNS effects: drowsiness, dizziness, ataxia, nausea, vomiting, hyperkinesia, hypotension, hyponatremia, coma, and status epilepticus. Cardiac conduction abnormalities (bradycardia, arrhythmias) may occur.
Storage: Store below 30°C in a cool, dry place, protected from light and moisture. Keep out of reach of children. Do not use after the expiry date printed on the pack.