Behavioral and physiological effects of remifentanil and alfentanil in healthy volunteers

Background: The subjective and psychomotor effects of remifentanil have not been evaluated. Accordingly, the authors used mood inventories and psychom otor tests to characterize the effects of remifentanil Ln healthy, non-dig- abusing volunteers, Alfentanil was used as a comparator drug. Methods: Ten healthy volunteers were enrolled in a randomized, double-blind ed, placebo-controlled, crossover trial in which they received an infusion of saline, remifentanil, or alfentanil for 120 min. The age- and weight-adj usted infusions (determined with STANPUMP, a computer modeling software pac kage) were given to achieve three predicted constant plasma levels for 40 m in each of remifentanil (0.75, 1.5, and 3 ng/ml) and alfentanil (16, 32, an d 64 ng/ml), Mood forms and psychomotor tests were completed, and miosis wa s assessed, during and after the infusions. In addition, analgesia was test ed at each dose level using a cold-presser test. Results: Remifentanil had prototypic mu-like opioid subjective effects, imp aired psychomotor performance, and produced analgesia. Alfentanil at the do se 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 use d, may exist between remifentanil and alfentanil. A psychomotor test admini stered GO 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 ar e extremely short-lived after the drug is no longer administered must be qu estioned given our findings that psychomotor effects were still apparent 1 h after the infusion was discontinued.