Alfentanil hydrochloride: a new short-acting narcotic analgesic for surgical procedures

The chemistry, pharmacology, pharmacokinetics, clinical use, adverse effects, dosage, and administration of the short-acting synthetic narcotic analgesic alfentanil hydrochloride are reviewed. Alfentanil is a tertiary amine with an ionization constant of 6.5, resulting in approximately 10% ionization at physiologic pH. When compared with fentanyl, alfentanil has a faster onset and one third the duration of action, one fourth to one tenth the potency, less lipid solubility, greater protein binding, and a much greater unionized fraction at physiologic pH. Alfentanil is approximately 20-40 times less potent than sufentanil on a weight basis, but it has a faster onset and shorter duration of action. After i.v. injection, alfentanil is distributed in the body according to a two- or three-compartment model. When given to young and middle-aged patients for various surgical procedures, alfentanil has an elimination half-life of 70-99 minutes independent of the dose or route of administration. Clinical studies comparing alfentanil with fentanyl in short surgical procedures are reported; alfentanil produces earlier peak analgesic effect, faster recovery of consciousness, and a more pronounced narcotic effect without increased adverse effects. When alfentanil was given in high doses for anesthesia induction, chest-wall rigidity occurred frequently. Like fentanyl, alfentanil was found to produce a high incidence of nausea and vomiting. It was more effective when administered by infusion than by bolus. Alfentanil is useful for supplementation of analgesia for outpatient surgical procedures, as an infusion for maintenance of anesthesia during surgery, and perhaps as an induction agent.