Morphine: controlled trial of different methods of administration for postoperative pain relief

Forty-five patients who had undergone major operations were given a slow intravenous injection of morphine sulphate (1 mg/ml saline) until their pain was relieved and were then randomly divided into three equal groups to receive different regimens of morphine sulphate over the next 72 hours. Patients in group A received 3.5 times the pain-relieving dose (28-63 mg, mean 36 mg) by continuous intravenous infusion; those in group B received the pain-relieving dose (90-160 mg, mean 110 mg) intramuscularly, four-hourly for the first 24 hours, six-hourly for the next 24 hours, and then eight and 20 hours later; and those in group C received the pain-relieving dose (80-280 mg, mean 140 mg) intramuscularly as required. Pain was assessed on a linear analogue scale and vital capacity and peak expiratory flow rate measured 12-hourly. The mean pain score was significantly lower and respiratory function significantly better in group A than in groups B and C. Only one patient (in group A) required extra morphine. Thus morphine administered by continuous intravenous infusion is superior to other regimens, giving better pain relief at a lower dosage.