THE METABOLISM OF PHENYTOIN BY ISOLATED HEPATOCYTES AND HEPATIC MICROSOMES FROM MALE-RATS

  • 1 January 1982
    • journal article
    • research article
    • Vol. 222  (3) , 658-661
Abstract
Previous in vivo and in vitro studies have indicated that the Km for phenytoin hydroxylation is .apprx. 30 .mu.M. Yet, the drug shows dose-dependent kinetics sugesting a Km of .apprx. 5 .mu.M. The discrepancy is evidently not due to active transport of the drug in the hepatocyte or a decrease in the Km due to the low pO2 [partial pressure of O2] of the portal vein leading to uncompetitive inhibition [of ethylmorphine-N-demethylase]. Studies in both hepatocytes and microsomes indicate the presence of a high-affinity hydroxylase with a Km of 2-5 .mu.M. This enzyme is the one primarily involved in phenytoin metabolism.

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