Pharmacology · Antiseizure medicines
Topiramate !
An antiseizure and migraine-prevention medicine with several targets. It causes weight loss, tingling, slowed thinking and kidney stones.
Updated 2026-11-01
The figure shows topiramate bound to human carbonic anhydrase II, one of its targets. Inhibiting this enzyme explains metabolic acidosis and kidney stones; the antiseizure effect also involves sodium channels, GABA-A and AMPA/kainate receptors.
Mechanism of action
Topiramate blocks voltage-gated sodium channels, strengthens GABA at some GABA-A receptor subtypes and blocks the AMPA/kainate type of glutamate receptor. It also inhibits carbonic anhydrase, which causes metabolic acidosis, kidney stones and less sweating.
- Blocks voltage-gated sodium channels
- Strengthens GABA at some GABA-A receptors
- Blocks AMPA/kainate glutamate receptors
- Also inhibits carbonic anhydrase (acidosis, stones)
Pharmacokinetics
- Absorption
- Absorbed by mouth
- Metabolism
- Not extensively metabolized
- Elimination
- About 70% unchanged in the urine; the dose is adjusted in kidney disease
- Half-life
- About 21 hours
Indications
- Focal and generalized tonic-clonic seizures, and seizures of Lennox-Gastaut syndrome Epilepsy and seizures →
- Migraine prevention (not for an attack already under way) Migraine →
Adverse effects
Common
- Tingling (paraesthesia)
- Loss of appetite and weight loss
- Slowed thinking, word-finding and memory problems
- Altered taste
- Dizziness, fatigue and drowsiness
Contraindications
- None listed in the label; it is avoided with other carbonic anhydrase inhibitors and the ketogenic diet because of kidney stones
Key interactions
- Hormonal contraceptives
- Less contraceptive effect and breakthrough bleeding
- Valproate
- Hyperammonaemia, encephalopathy and hypothermia
- Other carbonic anhydrase inhibitors (acetazolamide, zonisamide)
- More metabolic acidosis and kidney stones
- Anticholinergic drugs
- More risk of heat-related illness
What is monitored
- Serum bicarbonate at baseline and periodically
- Eye symptoms: sudden blurred vision or eye pain
- Sweating and body temperature in children
- Weight, mood and cognition
Administration and safety
- Given by mouth; immediate- and extended-release forms are not swapped without care
- Good fluid intake helps prevent kidney stones
- Withdrawn gradually: stopping suddenly can trigger seizures
Nursing care
- Teach to report sudden blurred vision or eye pain at once
- Encourage plenty of fluids, and watch for flank pain or blood in the urine
- Watch children for reduced sweating and fever in hot weather
- Warn about slowed thinking before driving
- Remind that hormonal contraception may be less effective
Pregnancy and breastfeeding
Exposure in pregnancy raises the risk of cleft lip or palate and of a baby small for gestational age.
Test yourself
Think of the answer, then tap the question to see it.
Which eye emergency is linked to topiramate?
Acute myopia with secondary angle-closure glaucoma, usually in the first weeks; vision can be lost permanently if the drug is not stopped.
Why does topiramate cause kidney stones and metabolic acidosis?
It inhibits carbonic anhydrase, which lowers bicarbonate reabsorption and favours stone formation.
Besides epilepsy, what is topiramate used for?
Migraine prevention; it does not treat an attack that has already started.
Which birth defect is linked to topiramate in pregnancy?
Oral clefts (cleft lip and/or palate).
Related drugs
Related conditions
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Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.
Sources: Topiramate: MedlinePlus Drug Information (MedlinePlus (U.S. National Library of Medicine), 2026); DailyMed - TOPIRAMATE tablet, film coated (DailyMed (U.S. National Library of Medicine), 2026); ATCDDD - ATC/DDD Index (WHO Collaborating Centre for Drug Statistics Methodology, 2026).
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Representative model, for educational purposes only.