Which first-line drug prescribed for absence seizures most likely caused this result? A 2-year-old boy who started treatment for absence seizures 2 weeks ago presents to the physician with blistering around his nose and mouth. On examination, it is noted that there is an extensive shedding of the skin.

Ethosuximide

The correct answer is B. Ethosuximide is the only agent that is both used for absence seizures and associated with StevensJohnson syndrome. Ethosuximide is an antiepileptic indicated for absence seizures that works by blocking T-type calcium channels. A rare but severe adverse effect is drug-induced Stevens Johnson syndrome. This is characterized by blistering of the nasal, oral, and genital mucosa as well as the conjunctivae. Erythema, palpable purpura, and epidermal necrolysis may also ensue Answer A is incorrect. Carbamazepine is used to treat partial and tonic-clonic seizures, but not absence seizures. It acts by increasing sodium channel inactivation. Carbamazepine can cause diplopia, induction of the cytochrome P450 system, blood dyscrasias, liver toxicity, and StevensJohnson syndrome Answer C is incorrect. Lamotrigine is used to treat partial and tonic-clonic seizures, but not absences seizures. It acts by blocking voltagesensitive sodium channels. Lamotrigine can cause gastrointestinal upset, dizziness, diplopia, amnesia, and StevensJohnson syndrome Answer D is incorrect. Phenytoin is used to treat partial and tonic-clonic seizures, but not absence seizures. It acts by increasing sodium channel inactivation. Phenytoin toxicity causes nystagmus, diplopia, ataxia, gingival hyperplasia, hirsutism, and StevensJohnson syndrome Answer E is incorrect. Valproic acid is also indicated for absence seizures, and adverse effects include gastrointestinal distress and a rare, but fatal, hepatotoxicity. It acts by elevating concentrations of gamma-aminobutyric acid (GABA) in the brain. Valproic acid is not associated with StevensJohnson syndrome.