6 Interactions between intravenous anaesthetic agents

Interactions between intravenous anaesthetic agents can be either pharmacokinetic or pharmacodynamic. The clinical significance of a pharmacokinetic drug-drug interaction will depend on the magnitude of the change in the concentration of the drug at the site of pharmacological action. Intravenous anaesthetic agents can influence the distribution and elimination and/or the effect of other co-administered intravenous anaesthetic agents. Because of the larger pharmacodynamic variability (300–400%) compared to the pharmacokinetic variability (60–80%), pharmacodynamic interactions are more important clinically than pharmacokinetic interactions. Many pharmacodynamic interactions involving intravenous anaesthetics are synergistic, and this allows lower doses or concentrations to be used to achieve adequate depth of anaesthesia, with a corresponding reduction in the incidence of side-effects.