Analgesic efficacy and potency of two oral controlled-release morphine preparations

MS Contin tablets and Oramorph SR tablets are two forms of oral controlled-release morphine sulfate available for the alleviation of pain. Our objective was to compare their analgesic effects in a relative potency assay. In this study, 151 patients undergoing caesarean section or abdominal hysterectomy and reporting moderate or severe postoperative pain received a 30 or 90 mg dose of either drug in a balanced, randomized, double-blind, parallel-group, single-dose experimental design. Patients provided self-ratings of analgesia. Relative potency for pain relief were calculated from log dose-effect curves. For total pain relief (rated by visual analog scales) over 12 hours, the log dose relative potency estimate for MS Contin tablets/Oramorph SR tablets was 1.9 (95% confidence limits, 0.89 to 11.1); for peak pain relief (visual analog scales) the relative potency estimate was 1.7 (95% confidence limits, 0.65 to 48.3). Overall, the 90 mg dose of MS Contin was more effective than 30 or 90 mg doses of Oramorph SR and the 30 mg dose of MS Contin at hours 6 to 12. Adverse experiences (mainly drowsiness) were mostly mild to moderate, with no significant differences in their overall incidence or severity between equivalent doses. MS Contin tablets provided greater peak, total, and duration of analgesia, without higher incidence of adverse experiences.