Injected morphine in postoperative pain
Clinical bottom line:A 10 mg intramuscular dose of morphine is an effective analgesic. It has an NNT of 2.9 (2.6-3.6) for at least 50% pain relief over 4 to 6 hours compared with placebo in pain of moderate to severe intensity. The incidence of minor adverse effects is significantly higher with 10 mg intramuscular morphine compared with placebo.
Few trials of acceptable quality have been carried out. This is especially true for subcutaneous and intravenous studies.
Morphine is the archetypal analgesic for use in moderate or severe pain. It is the principle alkaloid of opium, and is given by many different routes. Morphine is the "gold standard" against which other injected analgesics are tested.
Systematic review
HJ McQuay, D Carroll, RA Moore. Injected morphine in postoperative pain: a quantitative systematic review. Journal of Pain and Symptom Management 1999; 17:164-74.
- Date review completed: March 1997
- Number of trials included: 20
- Number of patients: 1259 (696 active / 563 control; 494 treated patients for 10 mg dose)
- Control group: placebo
- Mainoutcomes: 4-6 hours TOTPAR or SPID; number-needed-to-treat (NNT) for 50% pain relief (with 95% confidence intervals); relative benefit (with 95% confidence intervals).
Inclusion criteria were full journal publication of trials of injected morphine in acute postoperative pain; single dose treatment of injected morphine and placebo (intravenous, intramuscular or subcutaneous); randomised; blinded design; moderate to severe baseline pain; adult populations.
For each trial the mean TOTPAR or SPID values for intramuscular morphine and placebo groups were converted to the percent of maximum total pain relief based on the categorical pain scales (%maxTOTPAR or %maxSPID). These values were then converted to dichotomous information on the proportion, and then the number of patients, who achieved at least 50%maxTOTPAR. A number-needed-to-treat for at least 50% pain relief and the relative benefit of the treatment were then calculated. Adverse effects frequency data were used to calculate numbers-needed-to-harm and relative risk.
Findings
Morphine was given by intramuscular injection in all trials except one intravenous trial. Sufficient data for meta-analysis was available for 10 mg intramuscular morphine trials only. The NNT for 10 mg intramuscular morphine was 2.9 (2.6 to 3.6).
Figure: At least 50% pain relief with intramuscular morphine 10 mg compared with
placebo
Adverse effects
Minor adverse effects occurred in 34% of patients given intramuscular morphine compared with 23% with placebo. This was significantly higher than placebo, with an NNH of 9.1 (5.6 to 27). There was no difference between morphine and placebo with major adverse effects (drug-related study withdrawal).
Related topics
- League table of analgesics
- NNT
- Relative benefit/risk
- Identifier AP014 - 2101 IM MORPHINE: Jul-99