Relative reinforcing effects of three opioids with different durations of action. J Pharmacol Exp Ther

The role of duration of action on the relative reinforcing effects of three opioid drugs (fentanyl, alfentanil, and remifentanil) was eval-uated. Duration and onset of action were determined using mea-sures of respiratory depression and antinociception after i.v. ad-ministration. Effects on minute volume of respiration indicated that each of the three opioids had immediate onsets of action after i.v. administration. Fentanyl’s duration of suppression of respiration and antinociception was longer than that of alfentanil, which was longer than that of remifentanil. Reinforcing strength was mea-sured in i.v. self-administration studies in which the fixed ratio resulting in drug administration was increased from one session to the next. Comparisons were made of the behavioral economic variables Pmax and area under the demand curve (Omax). Remifen-tanil maintained higher rates of responding than did alfentanil, an