Anticonvulsant hypersensitivity syndrome

Anticonvulsant hypersensitivity syndrome is a rare disorder which occurs after administration of phenytoin, phenobarbitone or carbamazepine. It may be distinguished from a simple drug rash by the presence of fever, hepatitis, haematological abnormalities and other signs of systemic disease. These drugs all contain a benzene ring which is thought to form a toxic metabolite called arene oxide. This highly electrophilic molecule covalently binds to molecules and causes cell death. This compound is normally detoxified by the enzyme epoxide hydroxylase. Those individuals with impaired or absent activity of the enzyme will manifest the syndrome. In the unborn foetus, lack of this enzyme will predispose the child to developing foetal hydantoin syndrome. Treatment consists of removing the offending agent and supportive care. The use of steroids remains controversial.