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Topiramate neurochemistry — MRCPsych Paper A MCQ

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HardNeurophysiology and neurochemistryTopiramate neurochemistryMRCPsych Paper A

A 32-year-old man with binge-eating disorder and frequent migraine is started on a licensed migraine-preventive medicine. His headaches improve and he loses weight, but he develops paraesthesia and prominent word-finding difficulty. Which pharmacodynamic profile best identifies the medicine?

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Correct answer: D — Use-dependent sodium-channel blockade, GABA-A potentiation and AMPA/kainate receptor antagonism

The medicine is topiramate, identified by its use in migraine prevention together with weight loss, paraesthesia and language-related cognitive adverse effects. Topiramate has several actions: use-dependent blockade of voltage-gated sodium channels, potentiation of inhibitory GABA signalling at GABA-A receptors, and antagonism of excitatory glutamate transmission at AMPA/kainate receptors. It also weakly inhibits carbonic anhydrase. Option E describes vigabatrin; option B describes gabapentin or pregabalin; option A describes tiagabine; and option C describes levetiracetam or brivaracetam. These are credible antiseizure-drug mechanisms but do not fit topiramate's distinctive multimodal pharmacology and clinical adverse-effect pattern.

Reference: electronic Medicines Compendium. Topiramate Morningside 100 mg Film-coated tablets, Summary of Product Characteristics, section 5.1 Pharmacodynamic properties. Updated 10 March 2025. https://www.medicines.org.uk/emc/product/100615/smpc