ABSTRACT
The inhibitor can bind reversibly or irreversibly. Reversible enzyme inhibitors may be subject to competition from the endogenous ligand and their action ceases when they are metabolized or excreted. Their action is not dependent on permanent bonds, they have to be administered regularly or by infusion (e.g. aminophylline), and their actions stop with cessation of treatment. Conversely, irreversible inhibitors usually form stable (sometimes covalent) bonds with the enzyme. In such a case, deactivation may depend on cellular turnover and synthesis of new enzymes. Examples of such drugs are organophosphorus compounds and monoamine oxidase inhibitors. It may be weeks before the action of these drugs is overcome by normal cellular mechanisms. Drugs encountered in anaesthetic practice which inhibit enzymes are given in Table 19.14.
