Pharmacokinetics of the infusion of alfentanil in man

The pharmacokinetics of alfentanil under the conditions of an empirically derived 1-h continuous infusion of 3 micrograms kg-1 min-1, with a bolus of 80 micrograms kg-1, both i.v., were determined in five patients. The distribution half-life (mean +/- SD) (7.4 +/- 3.1 min), elimination half-life (86.7 +/- 15.8 min), apparent volume of distribution, Varea (0.44 +/- 0.15 litre kg-1) and elimination clearance (3.33 +/- 0.75 ml kg-1 min-1) were similar to those previously reported for a single bolus of alfentanil. These values for apparent volume of distribution and clearance can be used to calculate correct bolus and infusion doses to maintain any desired steady state plasma concentration using standard formulae: for example, to maintain a steady state plasma concentration of 400 ng ml-1, a bolus dose of 176 micrograms kg-1 and an infusion of 1.3 micrograms kg-1 min1 would be required.