Assessment of oral S+ ketamine associated with morphine for the treatment of oncologic pain.

BACKGROUND AND OBJECTIVES Morphine is used frequently to treat oncologic pain. However, tolerance may develop with prolonged use. The association of a NMDA receptor antagonist may reduce or delay the onset of tolerance. S(+) ketamine seems to be more potent and with fewer side effects. The aim of this study was to evaluate the association of S(+) ketamine and morphine in the treatment of oncologic pain. METHODS Thirty patients, randomly divided in two groups, participated in this double-blind study. Patients in G1 received 10 mg of morphine PO every 6 hours and 10 mg of S(+) ketamine PO every 8 hours. Patients in G2 received 10 mg of morphine PO every 6 hours and placebo PO every 8 hours. The dose of morphine was adjusted by 5 mg increments whenever necessary. Pain severity was evaluated through a verbal scale. RESULTS The percentage of no pain and mild pain was similar in both groups (G1 = 0 and G2 = 0 at M0; G1 = 22.2 and G2 = 53.8 at M1; G1 = 22.2 and G2 = 61.5 at M2; G1 = 44.6 and G2 = 61.5 at M3; and G1 = 44.5 and G2 = 53.8 at M4); Chi-square test. The percentage of moderate relief and complete relief was similar in both groups (G1 = 33.4 and G2 = 53.9 after one week; G1 = 44.4 and G2 = 69.2 after two weeks; G1 = 66.6 and G2 = 69.2 after three weeks; and G1 = 55.6 and G2 = 53.9 after four weeks); Chi-square test. The need to increase the dose of morphine was also similar in both groups (G1 = 2.22 and G2 = 2.15); Mann-Whitney test. CONCLUSIONS We did not observe an increase on the analgesic effects of morphine with the association of 10 mg of S(+) ketamine PO in the treatment of oncologic pain.