Trimethoprim-Sulfamethoxazole-Induced Hepatitis in Mixed Connective Tissue Disease

Trimethoprim-Sulfamethoxazole (TMP-SMZ) is associated with severe hepatic toxicity or liver failure. We present a case of severe hepatic toxicity for whom TMP-SMZ was prescribed as part of treatment for mixed connective tissue disease (MCTD). TMP-SMZ was used to prevent complications from steroid therapy, but fever and hepatic toxicity developed with repeated TMP-SMZ medication. While the drug lymphocyte stimulation test (DLST) for TMP-SMZ showed negative, the genotype for N-acetyltransferase 2 (NAT2) showed type *6/*7, which is the slow acetylating type for NAT2 activity. This finding for NAT2 genotype and the patient’s clinical history lead us to speculate that her fever and hepatic toxicity were caused by TMP-SMZ.