Injected morphine in postoperative pain: A quantitative systematic review

This systematic review of single-dose, placebo-controlled, randomized trials assessed pain relief from subcutaneous, intramuscular or intravenous morphine compared with placebo in postoperative pain. Pain relief or pain intensity difference over 4 to 6 hours was extracted and converted into the number of patients with at least 50 % pain relief. This was used to calculate the relative benefit and the number-needed-to-treat (NNT) for one patient to achieve at least 50 % pain, relief In 15 trials, comparing intramuscular morphine 10 mg (486 patients) with placebo (460 patients) morphine had an NNT of 2.9 (95 % confidence interval 2.6-3.6). This meant that one of every three patients with moderate or severe postoperative pain treated with 10 mg intramuscular morphine had at least 50 % pain relief and would not have achieved this had they been given placebo. Minor adverse effects were more common with morphine (34 %) than with placebo (23 %) (relative risk 1.49 [1.09-2.04]), but drug-related study withdrawal was rare (1.2 % overall) and no different from placebo. J Pain Symptom Manage 1999;17:164-174. (C) U.S. Cancer Pain Relief Committee, 1999.