Sensitivity to a metabolite of diclofenac as a cause of acute immune hemolytic anemia

A 75-year-old woman taking the nonsteroidal anti-inflammatory drug diclofenac (DCF) presented with acute Coombs-positive hemolytic anemia and subsequently developed renal failure. A drug-dependent antibody specific for red blood cells (RBCs) could not be demonstrated by in vitro testing with DCF. However, her serum was found to contain an IgM antibody that reacted strongly with RBCs in the presence of urine from any of four subjects who had ingested DCF. The active substance in urine was isolated, subjected to high-performance liquid chromatographic (HPLC) analysis, and found to be a glucuronide conjugate of a known DCF metabolite, 4'-hydroxydiclofenac (4'-OH DCF). Negative results were obtained with four other DCF metabolites. Two 4'-OH DCF glucuronides were synthesized in vitro using a liver microsomal system. One promoted agglutination of normal RBCs by the patient's serum and was identified as the glucuronide ester of 4'-OH DCF by proton nuclear magnetic resonance (NMR) analysis. Studies with a panel of RBCs showed that the patient's antibody reacted preferentially with the e antigen of the Rh system. Acute immune hemolytic anemia in this patient appears to have been caused by sensitization to DCF modified by 4' hydroxylation and glucuronidation. This is the first reported example of immune cytopenia caused by sensitivity to a glucuronide conjugate of a drug metabolite. Since glucuronidation is a common pathway of drug metabolism, studies of the frequency with which glucuronide derivatives of primary medications cause immune cytopenia seem warranted.