CLINICALLY SIGNIFICANT DRUG-INTERACTIONS WITH GENERAL-ANESTHETICS - INCIDENCE, MECHANISMS AND MANAGEMENT

The frequency of adverse drug interactions increases disproportionatel y with the increase in the number of drugs given to patients. It was s hown that 40% of patients given 16 drugs experienced an adverse drug i nteraction, compared with 5% of patients given fewer than 6 drugs. The magnitude of the drug interaction problem increases substantially in anaesthetised patients because of: (i) the increased use of multiple d rugs in the preoperative and intraoperative periods; and (ii) the grow ing population of geriatric patients who, in addition to having dimini shed drug metabolising capacity, are often prescribed multiple medicat ions for concomitant medical illness. Drug interactions with volatile and intravenous anaesthetics can be divided into those that are pharma cokinetic and pharmacodynamic in nature. Pharmacokinetic interactions occur when the absorption, distribution, metabolism or excretion of a drug is altered by the coadministration of a second drug. Pharmacodyna mic interactions involve a change in the pharmacological effect of a d rug as a result of the action of a second drug at receptor sites. An i nteraction between drugs, if not recognised and corrected, can result in decreased drug efficacy or serious toxicity. It is essential that c areful scrutiny of the patient's drug history is an integral part of t he preoperative assessment.