Valproic acid and immune thrombocytopenia.

During the course of a prospective serial study over a period of one year, findings compatible with immune-mediated thrombocytolysis accompanied the administration of valproic acid in about half of 45 children with epilepsy. Thrombocytopenia occurred in 15 and neutropenia in 12 patients, but was transient and self-limiting in each. The association is probably one of cause and effect, and it may reflect the structural similarity between valproic acid and constituents of cell membranes.