Inhibition of Drug Metabolizing Enzyme:

Several drugs or chemicals have the ability to decrease the drug metabolizing activity of certain enzymes known as enzyme inhibition. It can be either non-specific of microsomal enzymes or specific of some non-microsomal enzyme. Inhibition of hepatic microsomal enzyme mainly occurs due to administration of hepatotoxic agents, which cause either rise in rate of enzyme degradation of fall in the rate of enzyme synthesis. Nutritional deficiency, hormonal imbalance, or hepatic dysfunction also inhibit microsomal enzymes indirectly. When structurally similar compounds compete for the active site on the enzymes, there is inhibition of non-microsomal enzymes.

Enzyme inhibition generally results in depressed metabolism of drugs. As a result, plasma half-lives, duration of action, and efficacy as well as toxicity of the object drugs are significantly enhanced. They may also produce undesirable drug interactions.