A 6-year-old child is brought with sudden-onset staring episodes lasting 5–10 seconds with eye blinking, occurring >20 times daily. EEG confirms 3 Hz spike-and-wave discharges. The drug of choice and its primary mechanism are:

• A Phenytoin — blocks voltage-gated Na+ channels
• B Carbamazepine — stabilises Na+ channels in inactive state
• C Ethosuximide — blocks T-type Ca2+ channels in thalamic neurons ✓
• D Levetiracetam — binds SV2A synaptic vesicle protein

Explanation

Ethosuximide is the drug of first choice for pure childhood absence epilepsy. Its primary mechanism is selective inhibition of T-type (transient, low-voltage-activated) calcium channels in thalamo-cortical relay neurons, thereby suppressing the oscillatory burst firing responsible for the characteristic 3 Hz spike-wave pattern. Phenytoin and carbamazepine are contraindicated as they can worsen absence seizures.

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

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Written and medically reviewed by the StethoPrep medical team.