Alfentanil used in the aged: a clinical comparison with its use in young patients.

The clinical effects of an i.v. bolus dose of 50 micrograms kg-1 alfentanil were studied during surgical anaesthesia in 10 elderly patients and compared with those of the same dosage in nine young adults. Plasma samples, to determine alfentanil concentrations, were taken at regular intervals during the first hour following injection. Cardiovascular changes were minor. A transient fall in systolic blood pressure shortly after the alfentanil administration was seen in both groups but was more pronounced in the elderly patients. The quality of initial intra-operative analgesia was good in all patients. The duration of action of 50 micrograms kg-1 alfentanil, as judged by the occurrence of signs of insufficient analgesia, was longer in the elderly patients (mean: 36 min) than in young patients (mean: 22 min). The alfentanil plasma levels extrapolated for these time points were similar. Hence, the difference in duration of action must be due to the slower elimination from the body in the elderly patient, rather than an increased sensitivity. On these grounds, age should be one of the criteria for selecting the appropriate dose of alfentanil.