Effects of paracetamol and acetylsalicylic acid on the post-operative course after experimental orthopaedic surgery in dogs.

In placebo-controlled cross-over trials in dogs, two 'identical' operations were performed on the forelimbs of each animal with an interval of 28 days, to evaluate how daily doses of 1.5 g paracetamol, 1.5 g acetylsalicylic acid (ASA) and 0.5 g ASA might modulate an acute post-operative inflammatory reaction. On the third post-operative day the reductions in swelling compared with placebo averaged 33% with 1.5 g paracetamol (P = 0.02), 24% with 1.5 g ASA (P = 0.03) and 15% with 0.5 g ASA (P = 0.18); while the reductions in pain estimates averaged 47% with 1.5 g paracetamol (P = 0.01), 32% with 1.5 g ASA (P = 0.07) and 28% with 0.5 g ASA (P = 0.21). There were no clinical signs of adverse drug effects, such as vomiting, haematochezia, cyanosis or depression. The results disagree with the traditional view that paracetamol has little or no anti-inflammatory effect, and demonstrate that paracetamol may reduce an acute inflammatory reaction, at least as efficiently as ASA. The potential pro-inflammatory effect of ASA in low doses is discussed. It is concluded that paracetamol appears to be a valuable drug against post-operative or post-traumatic sequelae in the veterinary as well as in the human clinic.