Total and free plasma and total synovial fluid piroxicam concentrations: relationship to antiinflammatory effect in patients with reactive arthritis and other arthritides.

Twenty-five patients (14 males, 11 females), sixteen with reactive arthritis and 9 with other arthritides were treated with piroxicam, 40 mg at day 1 and 20 mg daily the following 9 days. Both local knee joint and general disease activity were assessed at day 0 and day 10. At day 10, plasma and synovial fluid were drawn. Total and free (determined after equilibrium dialysis) plasma concentrations and total synovial fluid concentrations were measured by HPLC. Total plasma piroxicam concentrations (micrograms/ml) were 4.1 (0.5-8.3) [median (range)], free piroxicam plasma concentrations were 0.051 (0.012-0.118), total synovial fluid concentrations were 2.2 (0.3-4.6) and ratios total synovial to total plasma concentration were 0.51 (0.39-0.90). The effect of piroxicam treatment varied among the patients. We found no relationship between drug concentration and change in any of the disease activity parameters nor any correlation between the ratio of synovial fluid to plasma piroxicam concentration and the local knee joint disease activity parameters.