Induction of Drug Metabolizing Enzymes:

Several drugs and chemicals have the ability to increase the drug metabolizing activity of certain enzymes; referred to as enzyme induction. These drugs are known as enzyme inducers. They mainly interact with DNA and cause an increase in weight of liver, proliferation of SER and enhance the synthesis of microsomal enzyme proteins especially cytochrome P-450 and glucuronyl transferase. As a result, there is enhanced metabolism of those endogenous substance and drugs those are metabolized by microsomal enzymes. Enzyme inducers are generally lipid soluble compounds with relatively long plasma half-lives. Repeated administration of inducers for a few days is often required to induce enzyme and on stoppage of drug administration, the enzymes return to their original value over 1-3 weeks. Eg; Rifampicin, Ethanol, Carbamazepine, etc.

Clinical importance of enzyme inducers:

• It reduces efficacy and potency of drugs metabolized by these enzymes.
• It reduces plasma half-lives and duration of action of drugs
• It enhances drug tolerance
• It increases drug toxicity by enhancing concentration of metabolite, if metabolite is toxic. It increases chances of drug interactions.
• It alters physiological status of animal due to altered metabolism of endogenous compounds like sex steroids.