Behavioral and Physiological Effects of Remifentanil and Alfentanil in Healthy Volunteers

Abstract

Background The subjective and psychomotor effects of remifentanil have not been evaluated. Accordingly, the authors used mood inventories and psychomotor tests to characterize the effects of remifentanil in healthy, non-drug-abusing volunteers. Alfentanil was used as a comparator drug. Methods Ten healthy volunteers were enrolled in a randomized, double-blinded, placebo-controlled, crossover trial in which they received an infusion of saline, remifentanil, or alfentanil for 120 min. The age- and weight-adjusted infusions (determined with STANPUMP, a computer modeling software package) were given to achieve three predicted constant plasma levels for 40 min each of remifentanil (0.75, 1.5, and 3 ng/ml) and alfentanil (16, 32, and 64 ng/ml). Mood forms and psychomotor tests were completed, and miosis was assessed, during and after the infusions. In addition, analgesia was tested at each dose level using a cold-pressor test. Results Remifentanil had prototypic micro-like opioid subjective effects, impaired psychomotor performance, and produced analgesia. Alfentanil at the dose range tested had more mild effects on these measures, and the analgesia data indicated that a 40:1 potency ratio, rather than the 20:1 ratio we used, may exist between remifentanil and alfentanil. A psychomotor test administered 60 min after the remifentanil infusion was discontinued showed that the volunteers were still impaired, although they reported feeling no drug effects. Conclusions The notion that the pharmacodynamic effects of remifentanil are extremely short-lived after the drug is no longer administered must be questioned given our findings that psychomotor effects were still apparent 1 h after the infusion was discontinued.