Residual analgesic effects of morphine in 55 four-period crossover analgesic studies

Subjective response data from 55 postoperative pain studies were examined for the residual analgesic effects of morphine. The studies were planned as four-period crossover designs for four treatments. Each patient received 5 and 10 mg of morphine and two doses of a test preparation. Two measures of analgesia were used: Sum of the Pain Intensity Difference (SPID) and Total Pain Relief (TOTPAR). To facilitate analysis, two two-period groups were defined. Morphine data for periods 1 and 2 were designated as group A, and morphine data for periods 3 and 4 were designated as group B. Residual analgesic effects were 0.12 for both SPID and TOTPAR in group A and were 0.65 and 0.17 for SPID and TOTPAR, respectively, in group B. In these 55 studies, there was no evidence of significant residual analgesic effects. Thus the crossover design is an appropriate method for the evaluation of selected parenteral analgesics in the postoperative pain model.