Analgesic efficacy of parenteral paracetamol (propacetamol) and diclofenac in post-operative orthopaedic pain.

Background: Propacetamol is an injectable pro-drug of paracetamol (acetaminophen) with analgesic and antipyretic activities, especially used in the post-operative period. The aim of this study was to assess the analgesic efficacy and safety of intravenous paracetamol, administered as propacetamol, in comparison with placebo and intramuscular diclofenac in patients with post-operative pain.

Methods: This was a randomized, double-blind, double-dummy study. One hundred and twenty patients with moderate to severe pain following total hip arthroplasty received either two administrations of propacetamol 2 g intravenously, 5 h apart (n = 40), one single administration of diclofenac 75 mg intramuscularly (n = 40) or placebo (n = 40). Efficacy measures were assessed before each drug administration, for the 5 h following each study treatment administration and for the total study duration of 10 h. Safety was assessed by reporting adverse events and changes in vital signs, electrocardiogram (ECG) and biochemical investigations before and 24 h after dosing.

Results: Both active treatments were effective and statistically superior to placebo over the whole study period, as indicated by the total pain relief score. No significant differences were found between propacetamol and diclofenac for any measures of analgesic activity. Only minor and common adverse events were reported, with no overall differences between the groups.

Conclusion: Both active treatments were superior to placebo, and the overall efficacy of two intravenous infusions of propacetamol 2 g (equivalent to 1 g of paracetamol), 5 h apart, was not statistically different from that provided by a single intramuscular injection of diclofenac 75 mg over the first 5 h post-dose and over the total 10-h study period. The safety was good.