Adjunctive analgesia with intravenous propacetamol does not reduce morphine-related adverse effects.

BACKGROUND: Propacetamol is widely used in the management of postoperative pain. It decreases morphine requirements but its effect on the incidence of morphine-related adverse effects remains unknown.

METHODS: Patients (550) were randomly assigned to receive propacetamol or a placebo over the first 24 h after operation in a blinded study. Intravenous morphine titration was performed, after which morphine was administered s.c. every 4 h according to their pain score. Pain was assessed using a visual analogue scale (VAS). The primary end-point was the incidence of morphine-related adverse effects. The main secondary end-points were morphine requirements and VAS score.

RESULTS: After morphine titration, the VAS score and the number of patients with pain relief did not differ between groups. Morphine requirements were decreased in the propacetamol group (21 vs 14.5 mg, P<0.001) but the incidence of morphine-related adverse effects did not differ between groups (42 vs 46%, not significant). In patients with moderate pain (n=395), morphine requirements decreased by 37% (P<0.001) and the percentage of patients requiring no morphine was greater (21 vs 8%, P=0.002) in the propacetamol group. In patients with severe pain (n=155), morphine requirements decreased by 18% (P=0.04) in the propacetamol group and the number of patients who did not require morphine (3 vs 8%) did not differ significantly.

CONCLUSIONS: Although propacetamol induced a small morphine-sparing effect, it did not change the incidence of morphine-related adverse effects in the postoperative period. Moreover, no benefit could be demonstrated in patients with severe postoperative pain.