Anticonvulsant (Multiple Mechanisms) Pregnancy: Topiramate can cause fetal harm when administered to a pregnant woman. Pregnancy registry data indicate that infants exposed in utero have an increased risk of major congenital malformations, including but not limited to cleft lip and/or cleft palate (oral clefts), and of being small for gestational age (SGA); SGA has been observed at all doses and appears dose-dependent, with higher prevalence at higher doses and with continued use later in pregnancy. A pregnancy exposure registry (North American Antiepileptic Drug Pregnancy Registry, 1-888-233-2334) monitors outcomes.

Topiramate

Brand names: Topamax

Used in: Headache & Migraine

Topiramate is used for epilepsy (focal and generalised seizures) and for migraine prophylaxis.

Auto-extracted from the source labelling — not yet independently clinician-verified. These values were distilled from the UK SPC (or the US label where noted) but have not had a clinician sign-off. Confirm against the current SmPC before prescribing.

Adult dose

Dose: Monotherapy epilepsy (adults and patients 10 years of age and older): 400 mg/day in two divided doses, achieved by titration — week 1: 25 mg morning and 25 mg evening; week 2: 50 mg and 50 mg; week 3: 75 mg and 75 mg; week 4: 100 mg and 100 mg; week 5: 150 mg and 150 mg; week 6: 200 mg and 200 mg

Route: Oral — tablets can be taken without regard to meals; because of the bitter taste, tablets should not be broken

Frequency: Two divided doses daily

Max: Doses above 400 mg/day have not been shown to improve responses in adults with partial-onset seizures; for paediatric adjunctive therapy the total daily dose should not exceed 400 mg/day

Initial dose, titration and recommended maintenance dose vary by indication and age group. Adjunctive therapy epilepsy, adults 17 years and older: 200 to 400 mg/day in two divided doses for partial-onset seizures or Lennox-Gastaut syndrome, and 400 mg/day in two divided doses for primary generalized tonic-clonic seizures; initiate at 25 to 50 mg/day and titrate in increments of 25 to 50 mg/day every week (titrating in 25 mg/day weekly increments may delay time to an effective dose). Preventive treatment of migraine, patients 12 years and older: 100 mg/day in two divided doses — week 1: 25 mg evening only; week 2: 25 mg morning and 25 mg evening; week 3: 25 mg morning and 50 mg evening; week 4: 50 mg and 50 mg; dose and titration rate should be guided by clinical outcome and longer intervals between adjustments can be used if required. Monotherapy in patients 2 to 9 years of age is weight-based: initial 25 mg/day nightly for the first week, increased to 50 mg/day (25 mg twice daily) in the second week, then by 25 to 50 mg/day each subsequent week as tolerated, with target total daily maintenance doses (administered in two equally divided doses) of — up to 11 kg: 150 mg minimum to 250 mg maximum; 12 to 22 kg: 200 to 300 mg; 23 to 31 kg: 200 to 350 mg; 32 to 38 kg: 250 to 350 mg; greater than 38 kg: 250 to 400 mg. Withdraw topiramate gradually. Source note: no UK SPC posology was available in the fetched bundle — this draft is from US labelling and must be verified against the UK SPC.

Paediatric dose

Route: Oral

Frequency: Total daily dose given in two divided doses

Max: The total daily dose should not exceed 400 mg/day

Adjunctive therapy for pediatric patients 2 to 16 years of age with partial-onset seizures, primary generalized tonic-clonic seizures, or seizures associated with Lennox-Gastaut syndrome: the recommended total daily dose is 'approximately 5 to 9 mg/kg/day in two divided doses'. Titration should begin at 25 mg/day (or less, based on a range of 1 to 3 mg/kg/day) nightly for the first week; the dosage should then be increased at 1- or 2-week intervals by increments of 1 to 3 mg/kg/day (administered in two divided doses) to achieve optimal clinical response, guided by clinical outcome. A single per-kg figure is not stated — the label gives a range, so dosePerKg is left null. Safety and effectiveness below 2 years of age have not been established. Monotherapy dosing in patients 2 to 9 years is weight-band based, not per-kg (see adultDose.notes). Source: US labelling — verify against the UK SPC.

Dose adjustments

Renal

In patients with renal impairment (creatinine clearance less than 70 mL/min/1.73 m2), one-half of the usual adult dose is recommended. Patients undergoing haemodialysis may require a supplemental dose to avoid rapid drops in plasma concentration, taking into account the duration of the dialysis period, the clearance rate of the dialysis system and the patient's effective renal clearance of topiramate.

Dose auto-extracted from US FDA prescribing information (openFDA / DailyMed) — cross-check; US labelling may differ from UK — not yet clinician-verified. Always confirm against the product SmPC and your local formulary before prescribing.

US labelling (FDA)

Reference — US labelling, may differ from UK

Topiramate initial dose, titration, and recommended maintenance dose varies by indication and age group. See Full Prescribing Information for recommended dosage, and dosing considerations in patients with renal impairment, geriatric patients, and patients undergoing hemodialysis (2.1, 2.2, 2.3, 2.4, 2.5, 2.6) 2.1 Dosing in Monotherapy Epilepsy Adults and Pediatric Patients 10 Years of Age and Older The recommended dose for topiramate monotherapy in adults and pediatric patients 10 years of age and older is 400 mg/day in two divided doses. The dose should be achieved by titration according to the following schedule (Table 1): Table 1: Monotherapy Titration Schedule for Adults and Pediatric …

Source: US FDA prescribing information (openFDA / DailyMed), label dated 2026-06-08. Accessed 2026-06-12. US dosing and indications can differ from UK practice — use UK sources for prescribing decisions.

Contraindications

History of hypersensitivity reaction to topiramate or to any of the inactive ingredients of the tablet — anaphylaxis and angioedema have occurred

Side effects

Acute myopia and secondary angle closure glaucoma — can lead to permanent visual loss; discontinue as soon as possible. Visual field defects also reported
Metabolic acidosis — baseline and periodic measurement of serum bicarbonate is recommended
Cognitive/neuropsychiatric adverse reactions, including depression and mood problems; suicidal behavior and ideation
Oligohidrosis and hyperthermia, especially in paediatric patients
Hyperammonemia and encephalopathy (with and without concomitant valproic acid); kidney stones; decrease in bone mineral density and negative effects on growth (height and weight) in children
Note: the fetched label's incidence-ranked 'most common adverse reactions' list was truncated in the source bundle — the reactions above are the labelled serious/clinically significant reactions from §5/§6

Interactions

Phenytoin or carbamazepine — clinically significant decrease in plasma concentrations of topiramate; a dosage adjustment may be needed
Valproic acid — concomitant administration has been associated with hypothermia and hyperammonemia with and without encephalopathy; examine blood ammonia levels in patients in whom hypothermia is reported
Other carbonic anhydrase inhibitors (e.g. zonisamide, acetazolamide) — may increase the severity of metabolic acidosis and the risk of kidney stone formation; monitor closely
Contraceptives — decreased contraceptive efficacy and increased breakthrough bleeding, especially at doses greater than 200 mg/day
Lithium — monitor lithium levels if used with high-dose topiramate

Clinical monograph

How it works

It has multiple actions — sodium-channel blockade, enhancement of GABA, and carbonic-anhydrase inhibition — that together reduce neuronal excitability.

Prescribing in practice

It is teratogenic (cleft lip/palate and reduced fetal growth) and is subject to MHRA restrictions in those able to become pregnant — use highly effective contraception, and it reduces the efficacy of hormonal contraception at higher doses.
Cognitive effects (word-finding difficulty, slowing), weight loss, paraesthesia, renal stones, metabolic acidosis and acute glaucoma can occur.
Titrate slowly and do not stop abruptly; maintain hydration to reduce stone risk.

Monitoring

Review seizure/migraine control, weight, cognition and mood; in those able to become pregnant confirm pregnancy-prevention measures.

Counselling the patient

If you can become pregnant, use highly effective contraception and seek advice before any pregnancy.
Report tingling, eye pain or blurred vision, or loin pain (possible kidney stone).
Drink plenty of fluids; do not stop it suddenly.

Evidence & guidelines

Used for epilepsy and migraine prophylaxis (NICE NG217/NG150), with MHRA pregnancy-prevention requirements.

Reference: MHRA Topiramate Safety Review 2023; NICE NG217; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. The structured dose values shown have been reviewed by a clinician. Monograph status: clinician-reviewed (2026-07-04).

Curated clinical cross-links plus same-class fallbacks.

Calculators

Pathways