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Anticonvulsant (Multiple Mechanisms) Pregnancy: Avoid — MHRA Pregnancy Prevention Requirement (topiramate). Significant teratogenicity and neurodevelopmental risk.

Topiramate

Brand names: Topamax

Adult dose

Dose: Epilepsy: starting 25 mg OD at night × 1 week, increase by 25–50 mg every 1–2 weeks. Target: 200–400 mg/day BD. Migraine prophylaxis: 25 mg OD → 50 mg BD (target).
Route: Oral
Frequency: BD
Max: 400 mg/day (epilepsy); 100 mg/day (migraine prophylaxis)
Cognitive side effects ('topiramate fog') common — word-finding difficulties, slowed thinking. Weight loss (useful in obese epileptic patients). Kidney stones — adequate hydration essential. Acute myopia/angle-closure glaucoma (rare, within 1 month).

Paediatric dose

Dose: 0.5 mg/kg
Route: Oral
Frequency: Once daily at night (titration week 1; total 0.5–1 mg/kg/day, then divide BD as escalated)
Max: 9 mg/kg/day (max 400 mg/day epilepsy; 100 mg/day migraine prophylaxis)
Concentration: 15 mg, 25 mg sprinkle capsules; 25 mg, 50 mg, 100 mg, 200 mg tablets mg/ml
BNFc child ≥2 years: starting 0.5–1 mg/kg/day ON × 1 week, then increase by 1 mg/kg every 1–2 weeks; target maintenance 5–9 mg/kg/day in 2 divided doses. Sprinkle capsules can be opened. Cognitive AEs ('topiramate fog'); weight loss; renal stones (hydrate); acute myopia/angle-closure glaucoma (rare).

Dose adjustments

Renal

Halve dose if eGFR <70 — renally excreted

Hepatic

Caution in hepatic impairment

Paediatric weight-based calculator

BNFc child ≥2 years: starting 0.5–1 mg/kg/day ON × 1 week, then increase by 1 mg/kg every 1–2 weeks; target maintenance 5–9 mg/kg/day in 2 divided doses. Sprinkle capsules can be opened. Cognitive AEs ('topiramate fog'); weight loss; renal stones (hydrate); acute myopia/angle-closure glaucoma (rare).

Clinical pearls

  • MHRA 2023: topiramate in pregnancy — significant risk of neurodevelopmental disorders (autism, ADHD, intellectual disability) and structural abnormalities; MHRA PPRP (Pregnancy Prevention) applies
  • Acute angle-closure glaucoma: if acute onset eye pain/visual loss within first month — stop topiramate immediately and refer urgently to ophthalmology
  • Cognitive effects ('dopamax'): counsel patients; may be dose-dependent; reduce dose if significant
  • Metabolic acidosis: check bicarbonate levels periodically — symptomatic acidosis (hyperventilation, fatigue) requires dose reduction

Contraindications

  • History of kidney stones (relative — increases risk)
  • Pregnancy (MHRA 2023 teratogenicity warning)

Side effects

  • Cognitive impairment (word-finding, memory)
  • Weight loss (average 4–5%)
  • Nephrolithiasis (calcium phosphate stones — hydrate adequately)
  • Metabolic acidosis (carbonic anhydrase inhibition)
  • Paraesthesia (common, usually benign)
  • Acute angle-closure glaucoma (rare, first month)
  • Oligohidrosis/hyperthermia (children)

Interactions

  • Valproate — hyperammonaemia risk when combined (topiramate inhibits carnitine transport)
  • Combined OCP — topiramate at >200 mg/day reduces OCP efficacy
  • Phenytoin — increased phenytoin levels
  • Carbonic anhydrase inhibitors — increased kidney stone risk

Monitoring

  • Seizure frequency
  • Cognitive function (MOCA or clinical assessment)
  • Serum bicarbonate
  • Renal function and urinalysis (stones)
  • Weight

Reference: BNFc; BNF; MHRA Topiramate Safety Review 2023; NICE NG217. Verify against your local formulary and the latest BNF before prescribing.

Related

Curated clinical cross-links plus same-class fallbacks.

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