Sodium valproate inhibits seizures through multiple mechanisms. Which of the following mechanisms is considered most responsible for its broad-spectrum efficacy across absence, tonic-clonic, and myoclonic seizures?

• A Blockade of T-type calcium channels in thalamic relay neurons, interrupting the spike-wave pattern
• B Selective inhibition of carbonic anhydrase in glial cells, reducing bicarbonate-mediated depolarisation
• C NMDA receptor antagonism in the hippocampus preventing glutamate excitotoxicity
• D Combined effects: enhanced GABA transmission (via GABA-T inhibition and increased synthesis), sodium channel use-dependent blockade, and T-type calcium channel inhibition ✓

Explanation

Valproate's broad-spectrum activity stems from its multi-target mechanism: (1) it inhibits GABA transaminase (GABA-T) and succinic semialdehyde dehydrogenase, increasing GABA levels; (2) it augments GABA synthesis; (3) it blocks voltage-gated sodium channels in a use-dependent manner (effective for tonic-clonic); and (4) it inhibits T-type Ca2+ channels in thalamus (effective for absence). No other single mechanism alone explains its full spectrum. Ethosuximide has pure T-channel blockade (only for absence). Carbonic anhydrase inhibition is topiramate's and acetazolamide's mechanism.

Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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