Agonist-antagonist opioids: theory and clinical practice

Abstract

The agonist-antagonists are effective analgesics with some significant differences from the pure agonists. The clinical indications for these two classes overlap but are not identical. All of the agonist-antagonists have excellent safety profiles: life-threatening respiratory depression is uncommon, and minor toxic effects like nausea, constipation, and urinary retention occur less frequently than with morphine. Several of these agents have been widely available for over ten years, and during that time they have been subject to remarkably little diversion or abuse. There are at least three promising applications for these drugs in anaesthesia: 1 The kappa type drugs appear to be useful as sedatives and adjuncts to local or regional anaesthesia. We need better dosage guidelines for this indication and more data on interactions with other sedative drugs like benzodiazepines. 2 Epidural butorphanol has already shown some promise in obstetrics. A single dose provides relief of post-Caesarean pain for six to ten hours without pruritus or excessive sedation. 3 Finally, these analgesics may have advantages for Patient Controlled Analgesia, since they do not require locked pumps or narcotic inventory control. If the use of agonist-antagonists can significantly reduce pharmacy paperwork, their total costs will probably compare favourably with morphine and meperidine. © 1989 Canadian Anesthesiologists.