Full reports of randomised controlled trials of oral paracetamol combined with codeine for acute postoperative pain were sought. Different search strategies were used to identify eligible reports in MEDLINE (1966 - March 2000), EMBASE (1980 - March 2000), the Cochrane Library (Issue 3, 2000) and the Oxford Pain Relief Database (1950 - 1994) [16 (
link)]. Reference lists of retrieved reports and reviews [1 (
link),2 ] were searched for additional trials. Abstracts, review articles and unpublished reports were not considered.
Criteria for inclusion for postoperative pain were: full journal publication, randomised controlled trials which included single dose treatment groups of oral paracetamol combined with codeine, double blind design, baseline postoperative pain of moderate to severe intensity, patients over 15 years of age, at least 10 patients per group, and the pain outcome measures of total pain relief (TOTPAR) or summed pain intensity difference (SPID) over 4-6 hours or sufficient data provided to allow their calculation. Pain measures allowed for the calculation of TOTPAR or SPID were a standard five point pain relief scale (none, slight, moderate, good, complete), a standard four point pain intensity scale (none, mild, moderate, severe) or a standard visual analogue scale (VAS) for pain relief or pain intensity. Each report was scored for quality using a three item, 1-5 score, quality scale [6 (
link)].
For each trial, mean TOTPAR, SPID, VASTOTPAR or VASSPID values for each drug group were converted to %maxTOTPAR by division into the calculated maximum value [17 ]. The proportion of patients in each treatment group who achieved at least 50%maxTOTPAR was calculated using valid equations [18 (
link),19 (
link),20 (
link)]. The number of patients with >50%maxTOTPAR was then used to calculate relative benefit and NNT for paracetamol plus codeine versus placebo. Relative benefit and relative risk estimates were calculated with 95% confidence intervals (CI) using a fixed effects model [21 (
link)]. NNT with 95% confidence intervals was calculated by the method of Cook and Sackett [22 (
link)]. A statistically significant difference from control was assumed when the 95% confidence interval of the relative benefit did not include 1. Confidence intervals of proportions were calculated according to Morris and Gardner [23 ]. Calculations were performed using Excel v 5.0 on a Power Macintosh G3. Simulations and calculations of probability were conducted as described in Moore et al, 1998 [11 (
link)].
Smith L.A., Moore R.A., McQuay H.J, & Gavaghan D. (2001). Using evidence from different sources: an example using paracetamol 1000 mg plus codeine 60 mg. BMC Medical Research Methodology, 1, 1.