Topiramate (Topamax) 💊
⚠️ Topiramate is teratogenic and subject to UK pregnancy-prevention restrictions.
It is contraindicated in pregnancy for migraine prophylaxis and should not be used in women of childbearing potential unless the conditions of the Pregnancy Prevention Programme are fulfilled.
📖 About
- Check BNF entry here for latest dosing, contraindications, interactions and monitoring guidance.
- Topiramate is a broad-spectrum antiseizure medicine also used for migraine prophylaxis.
- It is sometimes used in weight management in specialist settings, but this is not a routine UK indication for standard topiramate monotherapy.
⚠️ Pregnancy Prevention Programme
- Do not use for migraine prophylaxis in pregnancy.
- In epilepsy during pregnancy, use only if there is no suitable alternative and after specialist risk–benefit assessment.
- In women and girls of childbearing potential, topiramate should not be prescribed unless Pregnancy Prevention Programme conditions are met.
- PPP conditions include documented counselling, effective contraception, pregnancy testing before initiation where appropriate, and regular specialist review.
- Patients should not stop topiramate suddenly if used for epilepsy; urgent specialist advice is needed because uncontrolled seizures may be dangerous.
⚙️ Mechanism of Action
- Blocks voltage-gated sodium channels → stabilises neuronal firing.
- Enhances GABA-mediated inhibitory neurotransmission.
- Antagonises AMPA/kainate glutamate receptors.
- Inhibits carbonic anhydrase isoenzymes → explains risk of renal stones and metabolic acidosis.
🧾 Indications
- Monotherapy or adjunctive therapy for focal seizures.
- Monotherapy or adjunctive therapy for generalised tonic-clonic seizures.
- Adjunctive therapy for seizures associated with Lennox–Gastaut syndrome.
- Migraine prophylaxis, subject to pregnancy restrictions.
💥 Side Effects
- Neurological: somnolence, dizziness, headache, ataxia, paraesthesia.
- Cognitive/psychiatric: impaired memory, word-finding difficulty, concentration problems, mood change, depression or rarely suicidal ideation.
- Weight: reduced appetite and weight loss.
- Renal: increased risk of kidney stones due to carbonic anhydrase inhibition.
- Ophthalmic: acute myopia and secondary angle-closure glaucoma, usually early after initiation.
- Metabolic: metabolic acidosis due to bicarbonate loss.
- Other: taste disturbance, nausea, fatigue and reduced sweating/heat intolerance, especially in children or hot weather.
🔄 Interactions
- Hormonal contraception: topiramate, especially at doses ≥200 mg/day, may reduce contraceptive effectiveness. Follow PPP contraception advice.
- May increase phenytoin levels; enzyme-inducing antiseizure medicines may reduce topiramate levels.
- Caution with other carbonic anhydrase inhibitors, e.g. acetazolamide or zonisamide → increased risk of acidosis and renal stones.
- CNS depressants and alcohol may worsen sedation, dizziness and cognitive impairment.
🧪 Monitoring
- Assess baseline pregnancy status and contraception requirements where relevant.
- Monitor cognition, mood, weight, appetite, paraesthesia, visual symptoms and hydration/renal stone risk.
- Check U&E, renal function and bicarbonate in patients with renal disease, symptoms of acidosis, recurrent stones, diarrhoea, ketogenic diet, interacting medicines or other risk factors.
- Therapeutic serum concentration monitoring is not routinely required, but if measured a commonly cited range is 5–20 mg/L.
💊 Dose — Adults
- Epilepsy: commonly start 25 mg at night, then increase gradually by 25–50 mg/week according to response and tolerability.
- Epilepsy maintenance: often 100–200 mg/day in divided doses for monotherapy; higher doses may be required in specialist care depending on indication and response.
- Adjunctive epilepsy therapy: usual total daily dose may be 200–400 mg/day in two divided doses.
- Migraine prophylaxis: start 25 mg at night and titrate gradually; usual target is 50–100 mg/day, often as 50 mg twice daily.
- ⚠️ Titrate slowly to reduce cognitive adverse effects, paraesthesia, dizziness and treatment discontinuation.
- Reduce dose or titrate more cautiously in renal impairment and frailty.
📚 References
