Biotransformation and toxicity of inhalational anaesthetics

In summary, anaesthetics and drugs used perioperatively are all xenobiotics and can be metabolized mainly by microsomal enzyme systems, which have a high activity in the liver. These enzyme systems are induced by repeated pre-administration of drugs, such as barbiturates and others which are used during the preoperative period. However, according to some reports, aerobic and anaerobic metabolism is inhibited by the simultaneous administration of drugs, such as isoflurane and halothane, halothane and enflurane, and cimetidine and halothane. Hypoxia is also an important factor in hepatic disorders and it is well known that anaerobic metabolism of halothane is increased by hypoxia and its intermediate production produces a free radical. Theoretically, this free radical is involved in hepatic disorders. In practice, in order to prevent hepatic dysfunction before, during and after anaesthesia, hypoxia and repeated pre-administration of enzyme-inducing drugs should be avoided. However, the choice and combination of drugs which inhibit drug metabolism and prevent hepato and/or nephro toxicity should be examined by further investigation.