EpilepsyRx

Topiramate

Topamax · Trokendi XR · Qudexy XR

DailyMed-verified antiseizure indications

Indication / use

Label / evidence summary
Topamax, Eprontia, and Qudexy XR: initial monotherapy or adjunctive therapy for focal-onset or primary generalized tonic-clonic seizures from age 2 years; adjunctive Lennox-Gastaut syndrome-associated seizure treatment from age 2 years. Trokendi XR has these epilepsy indications from age 6 years.
Role
Maintenance
Class
Multiple proposed actions: sodium channels, GABA-A, AMPA/kainate and carbonic anhydrase

Indications checked 26 September 2026. Product, route, age, and treatment-role limits apply. A DailyMed listing alone does not establish FDA approval.

Formulations & strengths

U.S. products unless another country is named. Strengths are per unit or stated volume.

Brand & formulation labels

Each link names the product and formulation it covers. Archived labels do not establish current availability.

Dosing & administration

Adult / product-specific schedule
Slow titration is standard. Epilepsy targets commonly 200–400 mg/day in divided doses, depending on regimen and indication.
Pediatric
Age 2–16 years adjunctive therapy: start 1–3 mg/kg/day; titrate to 5–9 mg/kg/day in two divided doses. Other indications and formulations have separate schedules.
Titration / repeat dosing
Adults: commonly 25–50 mg/day initially, increasing by 25–50 mg/week to 200–400 mg/day depending on indication. Pediatric adjunctive therapy: 1–3 mg/kg/day initially, titrating over 5–7 weeks to 5–9 mg/kg/day.

Dose adjustment & concentrations

Renal impairment
Use one-half usual adult dose when creatinine clearance <70 mL/min/1.73 m²; dialysis supplement may be needed.
Hepatic impairment
Use caution; clearance may be decreased.
Serum reference information
5–20 mcg/mL

Safety

Boxed warning
No boxed warning.
Contraindications
Hypersensitivity to topiramate or ingredients.
Serious precautions & monitoring
Cognitive effects, metabolic acidosis, nephrolithiasis, oligohidrosis, acute myopia/glaucoma, and fetal risk are key counseling points.

Common / selected adverse effects

  • Paresthesia
  • Weight decrease
  • Somnolence
  • Difficulty with memory
  • Anorexia
  • Dizziness

Drug interactions: toxicity & clinical action

Partner / combinationClinical effectClinical action
ValproateHyperammonemia/encephalopathy and hypothermia may occur even when either drug was tolerated alone.Check ammonia with unexplained lethargy, vomiting or altered mental status; review temperature and consider stopping a contributing drug.
Other carbonic anhydrase inhibitors / ketogenic dietHigher acidosis and kidney-stone risk.Monitor bicarbonate and renal symptoms; assess whether combined therapy is necessary.
Phenytoin / carbamazepineLower topiramate exposure; phenytoin may itself rise in some patients.Monitor seizure control and concentration-related neurotoxicity after changes.
Hormonal contraceptives / lithium / hydrochlorothiazideReduced contraceptive effectiveness (especially >200 mg/day); lithium exposure may rise at high topiramate doses; HCTZ increases exposure and potassium loss.Review contraception; monitor lithium, potassium and tolerability as relevant.

Pregnancy & contraception

Fetal / neonatal risk
Topiramate increases the risk of oral clefts and small-for-gestational-age birth. AAN/AES/SMFM advises avoiding it when clinically feasible to reduce fetal growth risk.
Contraception
Hormonal contraceptive effectiveness can fall, especially above 200 mg/day, and failure can occur without breakthrough bleeding. Use effective contraception and review the exact regimen.
Pregnancy / postpartum monitoring
Monitor maternal bicarbonate for metabolic acidosis; monitor newborns after in-utero exposure for acidosis.

Clinical evidence

Research summaries describe studied populations and outcomes; they do not add indications or constitute treatment recommendations.

Direct pivotal trial Guideline-supported off-label use

Trial summary

Study design / duration
Multicenter, randomized, double-blind, placebo-controlled adjunctive studies in focal seizures, generalized tonic-clonic seizures, and Lennox-Gastaut syndrome; baseline was followed by titration and fixed maintenance.
Primary endpoint
No single pivotal endpoint is identified in the cited source.
Results
Pivotal adjunctive focal-seizure studies generally showed median seizure reductions of approximately 27–48% at recommended doses versus roughly 1–13% with placebo; ≥50% responder rates increased with dose.

Trial publications

Mechanism of action

  • Preclinical studies identify four potentially contributing actions: voltage-dependent sodium-channel inhibition, GABA-A response enhancement at some receptor subtypes, AMPA/kainate receptor antagonism, and carbonic anhydrase inhibition (especially II and IV).
  • The relative contribution of each to seizure control is unresolved. GABA-A enhancement should not be assumed to mean action at the classical benzodiazepine site.
  • Carbonic anhydrase inhibition is also relevant to metabolic acidosis and kidney-stone risk; it is not simply another proven antiseizure pathway.

Pharmacology

Adult values unless specified. Vd/F denotes apparent oral distribution volume.

Pharmacokinetics

Bioavailability
Tablet bioavailability approximately 80% relative to oral solution; this is a relative comparison, not an absolute IV-referenced estimate. Food does not meaningfully affect absorption.
Elimination half-life
Approximately 21 hours in adults with normal renal function; shorter with enzyme inducers and often in children.
Volume of distribution
Apparent volume approximately 0.55–0.80 L/kg across single oral doses of 100–1,200 mg (UK SmPC); dose and sex influence estimates.
Active metabolite(s)
No clinically established active metabolite. Six metabolites are described; none individually represents more than 5% of the administered dose.
Active-metabolite half-life
Not applicable — no clinically established active metabolite.
Protein binding
15–41%
Metabolism / elimination
Mostly renal unchanged; partial hepatic metabolism

Renal clearance predominates. Do not apply high research-dose PK ranges as prescribing recommendations.

Molecular structure

Molecular structure of Topiramate
Principal compound; salt and product forms may differ.
NIH PubChem structure and record ↗

Product history

Initial U.S. approval
1996
Brands
Topamax · Trokendi XR · Qudexy XR
Manufacturer / marketer
Janssen (Topamax); Supernus (Trokendi XR/Qudexy XR)
Generic availability
Yes (immediate-release); ER products vary
Related drugs
Shares carbonic-anhydrase inhibition with zonisamide and acetazolamide.

Sources & review status

Representative sources are selected product labels, not an exhaustive list of generic manufacturers. Consult the exact product and formulation prescribed. Brand-name package inserts are linked separately.

Brand references: Topamax tablets / sprinkle capsules ↗ · Qudexy XR ↗ · Trokendi XR ↗

Indications and DailyMed PDFs checked: 2026-09-26. Other profile sources reviewed: 2026-09-15 · label revision noted at that review: 3/2026. This is a draft reference; final review is pending.

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