Loss of Warfarin Effect After Occupational Insecticide Exposure

NUMEROUS drugs have been reported to induce the metabolism of warfarin sodium, 1 and several chemicals in the environment are known to be inducers of oxidative drug metabolism. 2 There have been reports of enzyme induction in workers occupationally exposed to chlorinated hydrocarbon insecticides, in which the individuals were given test drugs, and half-lives were studied. 3 We report the case of a patient who demonstrated resistance to the hypoprothrombinemic effect of warfarin on two occasions after intense exposure to a chlorinated hydrocarbon insecticide mixture. Report of a Case A 53-year-old rancher was first admitted to Bernalillo County Medical Center, Albuquerque, NM, in December 1973, with the diagnosis of left femoral thrombophlebitis. He was treated with heparin sodium and warfarin and discharged taking warfarin sodium, 7.5 mg daily. His warfarin sodium dosage was increased to 10 mg alternating with 7.5 mg daily on Dec 28, 1973. On Jan 10, 1974,