Alkylation of the prosthetic heme in cytochrome P-450 during oxidative metabolism of the sedative-hypnotic ethchlorvynol.

The clinically used sedative-hypnotic ethchlorvynol destroys hepatic microsomal cytochrome P-450 enzymes in a process catalyzed by the same hemoproteins. Abnormal porphyrins accumulate in the livers of phenobarbital-pretreated rats after administration of ethchlorvynol. The abnormal porphyrin fraction has been isolated and shown to consist of the four possible regioisomers of N-(5-chloro-3-ethyl-3-hydroxy-2-oxo-4-pentenyl)protoporphyrin IX. Cytochrome P-450 inactivation thus appears to result from alkylation of the prosthetic heme by the oxidatively activated acetylenic function in ethchlorvynol. The autocatalytic destruction of the hemoprotein is likely to alter the metabolism and elimination of ethchlorvynol and coadministered drugs and may be the cause of the porphyrinogenic properties of ethchlorvynol.