ABSTRACT
No drug is suitable for prescribing unless it can be inactivated by metabolism, usually in the liver, and/or excreted, usually by the kidneys. The liver has a powerful battery of iso-enzymes, similar in structure and function but each specific only for the metabolism (bioconversion/transformation) of a particular group of drugs or poisons. The problem for the prescriber is that many effective and commonly used drugs interfere with the function of one or more of these P450 liver enzymes in one of two ways. Some drugs inhibit P450 enzymes, reducing their metabolic effectiveness, while others induce them, increasing their drug-metabolising function. If one drug inhibits a liver enzyme which is essential for the metabolism of other drugs, the plasma concentration of those drugs will increase and may reach toxic levels. A major risk of failing to understand enzyme induction is that the prescriber may attribute treatment failure to an inadequate dose, and increase the dose of the drug to compensate.
