For absence (petit mal) seizures, which drug is preferred?

• A. Ethosuximide
• B. Valproic acid
• C. Carbamazepine
• D. Lamotrigine

Answer: (A)

Absence seizures respond best to a drug that specifically targets the thalamocortical mechanisms underlying these events. Ethosuximide does just that by inhibiting T-type calcium channels in thalamic neurons, which reduces the rhythmic thalamocortical oscillations that produce the characteristic 3 Hz spike-and-wave discharges of absence seizures. This makes it highly effective for absence seizures while having minimal impact on other seizure types.

Valproic acid is effective and broad-spectrum, but its use is limited by risks such as hepatotoxicity and, importantly, teratogenicity, which is a major concern in women of childbearing potential. Carbamazepine works well for focal (partial) seizures and can even worsen absence seizures, so it’s not preferred for absence-dominant cases. Lamotrigine has a broader spectrum and can help some patients, but it isn’t as specifically effective as ethosuximide for pure absence seizures and is often reserved as add-on therapy.

So the best choice for a primary absence seizure regimen is ethosuximide because its mechanism directly targets the key thalamic driver of these seizures, providing strong efficacy with a favorable profile for this specific type.