Topiramate
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Topiramate
Topamax (IR), Trokendi XR, Qudexy XR, Eprontia (oral solution); component of Qsymia (with phentermine)
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Summary
Common uses
Partial-onset seizures (FDA, monotherapy and adjunct)0, Primary generalized tonic-clonic seizures (FDA, ages 2+)0, Lennox-Gastaut syndrome (FDA adjunct)0, Migraine prophylaxis (FDA, adult)0, Alcohol use disorder (off-label, evidence-supported)0, Binge-eating disorder and bulimia nervosa (off-label)0, Chronic weight management (Qsymia combination with phentermine, FDA)0
Pharmacy
Starting dose
Migraine: 25 mg PO at bedtime, titrate by 25 mg weekly to target 100 mg/day divided BID. Seizures: 25-50 mg/day, titrate weekly to 200-400 mg/day divided BID
Preparations
IR tablets 25, 50, 100, 200 mg; sprinkle capsules 15, 25 mg; Trokendi XR capsules 25, 50, 100, 200 mg; Qudexy XR capsules; Eprontia oral solution 25 mg/mL
US FDA Max
1600 mg/day (theoretical seizure dosing); practical use 400 mg/day for seizures, 100-200 mg/day for migraine prophylaxis
Pharmacology
Routes
Oral
Onset
Anticonvulsant effect within days at therapeutic level; migraine prophylaxis effect emerges over 2-3 months
Duration
12-24 hours (IR BID); 24 hours (ER once-daily)
Half-life
~21 hours[1]
Bioavailability
~80% (oral)[1]
Pregnancy
Substantial teratogenic risk including cleft lip/palate, hypospadias, and growth restriction (pregnancy registry data clear); effective contraception and pre-pregnancy counseling are required in reproductive-age patients[1]
Purported mechanism
Multi-target anticonvulsant: voltage-gated sodium channel blocker in the inactivated state, GABA-A receptor potentiator at a non-benzodiazepine site, AMPA/kainate glutamate receptor antagonist, and weak carbonic anhydrase inhibitor. The carbonic anhydrase inhibition explains the characteristic adverse-effect cluster (paresthesias, metabolic acidosis, kidney stones, oligohidrosis with heat intolerance) and likely contributes to the cognitive slowing nicknamed "dopamax" in clinical lore.0 Weight loss is a class effect, the basis of the Qsymia combination with phentermine for chronic weight management. Carbonic-anhydrase-related acute angle-closure glaucoma is a rare but vision-threatening idiosyncratic reaction, typically within the first month[1].