Morphine sulphate slow release. Comparison with i.m. morphine for postoperative analgesia.

Eighty patients undergoing abdominal surgery were studied after operation. Morphine was administered regularly every 4 h by either the i.m. (morphine sulphate 10 mg) or the oral route (MST Continus 20 mg) in a double-blind double-dummy trial. Both MST and i.m. morphine provided satisfactory postoperative analgesia, but significantly greater amounts of supplementary i.m. morphine were required in the MST group. More adverse effects were reported by the patients in the i.m. morphine group. The mean serum morphine concentration in 12 patients in the MST group was 1.7 ng ml-1 at 08.00 h and 19.5 ng ml-1 at 16.00 h on the 1st day after operation, suggesting impaired gastric emptying in the early postoperative period. It is therefore recommended that further studies of the bioavailability of MST in the early postoperative period be undertaken before any recommendations are made regarding its routine use for pain relief at that time.