Late antinociception and lower untoward effects of concomitant intrathecal morphine and intravenous buprenorphine in humans

Study Objective: To evaluate the perioperative antinociceptive effect of intrathecal morphine (a pure μ agonist), intravenous (IV) buprenorphine (a partial μ agonist) or their combination. Design: Randomized, double-blind, placebo-controlled study. Settings: Anesthesiology department of a university-affiliated public hospital. Patients: 45 ASA physical status I, II, and III patients undergoing hysterectomy with general anesthesia. Interventions: Preoperative and postoperative regimens consisted of intrathecal morphine 4.3 μg.kg^-1 plus IV 0.9% saline (Group 1), IV buprenorphine 1.3 μg.kg^-1 plus intrathecal saline (Group 2), and intrathecal morphine 4.3 μg.kg^-1 plus IV buprenorphine 1.3 μg.kg^-1 (Group 3; postoperative supplements consisting of IV buprenorphine 1.3 μg.kg^-1 plus intrathecal saline). Measurements and Main Results: Group 2 and 3 patients were given three analgesic dosings compared with two dosings in Group 1 (p < 0.001). The duration of action in Group 2 was significantly shorter (p = 0.001) than in the other two groups. The 12-hour postoperative pain intensity and sedation in Group 3 was significantly lower (p < 0.05) than in the other groups. Side effects (mainly pruritus and nausea and vomiting) were significantly fewer (p < 0.05) in Groups 2 and 3 (26% and 28%, respectively) than in Group 1 (46%). Conclusions: The concomitant administration of intrathecal morphine and IV buprenorphine alleviates pain sensation and minimizes sedation more effectively than when given after the administration of either drug separately. In addition, IV buprenorphine affords a reduction in side effects.