A 25-year-old woman with absence epilepsy is started on a drug that blocks T-type voltage-gated calcium channels in thalamic neurons, disrupting the 3 Hz spike-and-wave oscillations. Which drug is this?

• A Carbamazepine
• B Vigabatrin
• C Phenobarbital
• D Ethosuximide ✓

Explanation

Ethosuximide is the drug of choice for pure absence epilepsy. Its primary mechanism is blockade of T-type (low-threshold, transient) calcium channels in thalamic relay neurons, which disrupts the 3 Hz spike-and-wave oscillations characteristic of absence seizures. Carbamazepine blocks sodium channels and may worsen absence seizures. Vigabatrin inhibits GABA transaminase, increasing GABA concentrations. Phenobarbital enhances GABAergic inhibition but is a second-line agent for absence seizures.

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

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