Immune Thrombocytopenia Due to a Drug Metabolite

Abstract

A patient who developed thrombocytopenia while taking analgesics was found to have circulating antibody to a metabolic product of N-acetyl-p-aminophenol (NAPA), but not to the drug itself. The antibody reacted in vitro with an antigen present in the blood of a normal volunteer who had ingested NAPA. The antigenic material was purified from the urine of this volunteer and shown to be the sulfate conjugate of the drug. These findings demonstrate that a drug metabolite may be antigenically active in drug-induced thrombocytopenia when the drug itself is immunologically inert, representing a form of drug-induced thrombocytopenia.