Anti-hyperalgesic effects of nimesulide: studies in rats and humans

Nonsteroidal anti-inflammatory drugs (NSAIDs) are frequently used as analgesics. Despite the fact that clinical experience indicates a considerable disparity in the analgesic efficacy of NSAIDs, the animal models of nociception do not allow a clear distinction to be made between the analgesic properties of these agents. In contrast to nociceptive pain, clinical pain is characterised by hyperalgesia. Therefore, we evaluated the anti-hyperalgesic effects of the four NSAIDs nimesulide, diclofenac, celecoxib and rofecoxib which are widely used to treat inflammatory pain. We performed two animal studies in which each drug was administered intraperitoneally (i.p.) at its previously defined ED50 for the anti-inflammatory effect in the rat (i.e. the inhibition of carrageenan-induced hindpaw oedema measured by plethysmometry). In the first study, nimesulide (2.9 mg/kg) completely inhibited the development of thermal hindpaw hyperalgesia induced by the injection of formalin in the tail, whereas diclofenac (3.0 mg/kg) or celecoxib (12.7 mg/kg) partly reduced the hyperalgesia, and rofecoxib (3.0 mg/kg) was ineffective. In the second study, nimesulide and diclofenac were significantly more effective than celecoxib and rofecoxib in reducing the mechanical hindpaw hyperalgesia induced by the intraplantar injection of Freund's complete adjuvant (FCA). The anti-hyperalgesic activity of the drugs was also investigated in patients with rheumatoid arthritis. After a single oral dose, all drugs reduced the inflammatory hyperalgesia. However, only nimesulide was effective 15 minutes after treatment. Moreover, nimesulide (100 mg) was significantly more effective than rofecoxib (25 mg). Overall, our data demonstrate that NSAIDs may show different anti-hyperalgesic properties. Nimesulide seems to be particularly effective and fast-acting against inflammatory pain.