Background and aimBecausein vitrostudies have shown that nimesulide not only preferentially inhibits COX-2 but also reduces the action/release of pro-inflammatory cytokines, down-regulates the synthesis and/or activity of collagenase(s), and releases reactive oxygen species and other toxic substances from neutrophils, this study investigated whether nimesulide and ibuprofen could affect levels of biochemical markers of joint inflammation and collagen catabolism in patients with flare-up of knee or hip osteoarthritis.MethodsNinety patients were included in this randomised, prospective, single- blind study. They received either nimesulide (n = 45) or ibuprofen (n = 45) for a 4-week treatment period. The following parameters were analysed by ELISA: urinary levels of C-terminal cross-linking telopeptide of type II collagen (CTX-II), a marker of type II collagen breakdown; serum levels of hyaluronan (HA), a marker of synovial inflammation and hyperplasia; and circulating levels of stromelysin-1 (matrix metalloproteinase-3 [MMP-3]), collagenase-1 (MMP-1) and collagenase-3 (MMP-13). Statistical analysis used was ANOVA.ResultsAt the end of the treatment period, nimesulide but not ibuprofen markedly reduced the urinary levels of CTX-II (p < 0.001) and the serum levels of HA (p < 0.05), two markers known to prognosticate poor outcome of the osteoarthritis disease process. Nimesulide also reduced the serum levels of both MMP-3 (p < 0.05) and MMP-13 (p < 0.001). Furthermore, in the nimesulide group, the decrease in levels of CTX-II correlated significantly with the decrease in levels of HA and MMP-13.ConclusionAlthough nonsteroidal anti-inflammatory drugs are effective in improving pain and disability in OA patients, to date it has been unclear to what extent these drugs could affect joint metabolism and hence joint structure. Patients with flare-up of their osteoarthritis disease process exhibit enhanced levels of markers of joint inflammation and cartilage collagen breakdown, which were markedly decreased by nimesulide but not by ibuprofen.