To determine which class of non-opioid analgesics - paracetamol (acetaminophen), NSAIDs or COX-2 inhibitors - is the most effective at reducing morphine consumption and associated adverse effects when used as part of multimodal analgesia following major surgery.
A systematic literature review was conducted using MEDLINE, EMBASE and CENTRAL databases, searched from January 2003 to February 2009 and updating an earlier review.
Randomised controlled trials comparing paracetamol, NSAIDs or COX-2 inhibitors to each other or placebo, in adults receiving patient-controlled analgesia (PCA) with morphine following major surgery, were included. The COX-2 inhibitors rofecoxib and valdecoxib were excluded. Only trials that reported 24-hour morphine consumption were included. Other outcomes of interest were morphine-related adverse effects and adverse effects related to the non-opioids. Adequacy of randomisation, concealment of allocation, double blinding, and the flow of patients within the trial was assessed. The main analysis was a mixed treatment comparison (MTC) evaluating the relative effects of the four treatment classes. Four main outcomes were prioritised: 24-hour morphine consumption, sedation, nausea and vomiting, and surgical bleeding. Studies reporting nausea alone were pooled with studies reporting postoperative nausea and vomiting (PONV). Comparisons were described as statistically significant (at 5% level) when the credibility interval (CrI) did not cross 1 for odds ratio (OR) and zero for mean difference (MD). Trials making direct comparisons between the active interventions were also pooled in a meta-analysis using a random effects model. Sensitivity analyses were performed to assess the effects of study quality, individual drugs, and baseline morphine consumption.
Sixty relevant studies were identified. When paracetamol, NSAIDs or COX-2 inhibitors were added to PCA morphine, there was a statistically significant reduction in morphine consumption: paracetamol (MD -6.34 mg; 95% CrI -9.02 to -3.65); NSAIDs (MD -10.18; 95% CrI -11.65 to -8.72); and COX-2 inhibitors (MD -10.92; 95% CrI -12.77 to -9.08). NSAIDs and COX-2 inhibitors were both significantly better than paracetamol, and there was no significant difference between NSAIDs and COX-2 inhibitors (MD -0.74; 95% CrI -3.03 to 1.56). There was a significant reduction in nausea and PONV with NSAIDs compared to placebo (OR 0.70; 95% CrI 0.53 to 0.88) but not for paracetamol or COX-2 inhibitors, nor for NSAIDs compared to paracetamol or COX-2 inhibitors.
24-hour morphine consumption decreased by 6.3 mg to 10.9 mg, compared to placebo, when paracetamol, NSAID or COX-2 inhibitors were added to PCA morphine following surgery. Differences in effect between the three drug classes were small and unlikely to be of clinical significance. There does not appear to be a strong case for recommending routine addition of any of the three non-opioids to PCA morphine in the 24 hours immediately after surgery, or for favouring one drug class above the others.