The toxic effects of clofibrate and its metabolite on mammalian skeletal muscle: an electrophysiological study.

Membrane electrical parameters of rat extensor digitorum longus muscles were analysed in vitro, with intracellular microelectrodes, after chronic treatment with clofibrate or after in vitro application of chlorophenoxyisobutyric acid, the in vivo metabolite of clofibrate. Clofibrate caused only a 38% decrease in the membrane chloride conductance while its metabolite induced a large decrease of chloride conductance and drastic changes in the excitability characteristics of the muscles sampled. The capability of clofibrate to induce two types of myotonia is discussed.