Alfentanil infusions in patients requiring intensive care

Alfentanil is a short acting opioid that has an established place in anaesthesia. Its predictable pharmacokinetics and pharmacodynamics, particularly its rapid termination of effect and haemodynamic stability, have led to its use by continuous intravenous infusion both during anaesthesia and more recently in critically ill patients. Fine control of a potent analgesic that has respiratory depressant and antitussive properties would be particularly advantageous in this group, offering patients an improvement in comfort without increasing the risk of oversedation. Pharmacokinetic studies of alfentanil have demonstrated wide interindividual variations. This may be due to a wide variety of factors including age, obesity, hepatic dysfunction, changes in regional haemodynamics, sex, and alterations in plasma protein binding ability and concentration. The importance of pharmacogenetic differences and tolerance to alfentanil remains to be elucidated. Renal disease does not appear to significantly alter the pharmacokinetics of this agent, which may make it particularly useful in this situation. Since alfentanil does not depress conscious level or produce anxiolysis, additional agents such as a benzodiazepine will be necessary to provide adequate sedation. The difficulties in accurately predicting the response of an individual critically ill patient necessitate careful and continuous dose titration of alfentanil according to the clinical response.