Oral aspirin in postoperative pain: a quantitative systematic review.

Objectives: A systematic review of the analgesic efficacy and adverse effects of single-dose aspirin compared with placebo in postoperative pain.

Design: Published studies were identified from systematic searching of bibliographic databases and reference lists of retrieved reports. Summed pain intensity and pain relief data were extracted and converted into dichotomous information to yield the number of patients with at least 50% pain relief. This was used to calculate the relative benefit and number-needed-to-treat for one patient to achieve at least 50% pain relief. For adverse effects, relative risk and number-needed-to-harm were calculated. Sensitivity analyses were planned to test the impact of different pain models, pain measurements, sample sizes, quality of study design, and study duration on the results.

Results: Seventy-two randomized single-dose trials met our inclusion criteria, with 3253 patients given aspirin, and 3297 placebo. Significant benefit of aspirin over placebo was shown for aspirin 600/650 mg, 1000 mg and 1200 mg, with numbers-needed-to-treat for at least 50% pain relief of 4.4 (4.0-4.9), 4.0 (3.2-5.4) and 2.4 (1.9-3.2) respectively. Single-dose aspirin 600/650 mg produced significantly more drowsiness and gastric irritation than placebo, with numbers-needed-to-harm of 28 (19-52) and 38 (22-174) respectively. Type of pain model, pain measurement, sample size, quality of study design, and study duration had no significant impact on the results.

Conclusions: There was a clear dose-response for pain relief with aspirin, even though these were single dose studies. Adverse effects, drowsiness and gastric irritation were also evident in the single dose studies. The pain relief achieved with aspirin was very similar milligram for milligram to that seen with paracetamol.