Among organophosphorothioate (OPT) pesticides, malathion is considered relatively safe
for use in mammals. Its rapid degradation by carboxylesterases competes with the
cytochrome P450 (P450)-catalyzed formation of malaoxon, the toxic metabolite. However,
impurities in commercial formulations are potent inhibitors of carboxylesterase, allowing a
dramatic increase in malaoxon formation. Malathion desulfuration has been characterized in
human liver microsomes (HLMs) with a method based on acetylcholinesterase inhibition that …