No effect of 10 mg of oral S(+)-ketamine combined with morphine on postoperative analgesia

Summary Background and objectives Morphine is one of the most important analgesics for postoperative pain relief; however, opioids may cause hyperalgesia. NMDA receptor antagonists such as ketamine may reduce hyperalgesia. The aim of this study was to evaluate the efficacy of S (+)-ketamine associated to morphine for postoperative pain. Methods Thirty patients with pain after lower limb surgery and herniorraphy have been evaluated in a double-blind study, allocated into two groups. Group 1 patients received 10 mg of morphine + 10 mg of S (+)-ketamine (0.5 ml) PO; group 2 patients received 10 mg of morphine + placebo (0.5 ml). Pain intensity was evaluated by a numerical scale from 0 to 10 at the times: 0, 15, 30, 60, 120, and 240 min. Results There was no significant difference on pain intensity between groups (G1 = 7 ± 2.3 and G2 = 6.8 ± 2.9 at T0; G1 = 6.2 ± 2.2 and G2 = 6.0 ± 2.9 at T15; G1 = 3.6 ± 2.5 and G2 = 3.6 ± 3.4 at T30; G1 = 2.0 ± 2.4 and G2 = 1.7 ± 3.4 at T60; G1 = 1.8 ± 2.6 and G2 = 1.2 ± 3.3 at T120; G1 = 0.7 ± 1.8 and G2 = 1.4 ± 3.3 at T240; Mann–Whitney test). There was no difference on the time for first analgesic supplementation (G1 = 208.2 min and G2 = 215.3 min; Mann–Whitney test). The number of patients not requiring analgesic supplementation in G1 (26.7%) was higher than in G2 (6.7%), chi-square McNemar test. Conclusions There was no significant difference on pain intensity with the association of 10 mg of S (+)-ketamine to 10 mg of morphine for postoperative pain. There was a significant decrease of patients not requiring analgesic supplementation.