Concentration of carprofen in the serum and the synovial fluid in rheumatoid arthritis patients.

Concentrations of carprofen in the serum and the synovial fluid were determined in 13 patients with classical or confirmed rheumatoid arthritis. Four hours after the oral administration of 100 mg of carprofen, as one capsule, concentrations in the synovial fluid were found to be between 3.5 micrograms/ml and 9.7 micrograms/ml, with a mean value (+/- SD) of 6.2 +/- 1.4 micrograms/ml, and concentrations in the serum were between 4.7 micrograms/ml and 14.8 micrograms/ml, with a mean value of 9.8 +/- 2.9 micrograms/ml. The carprofen concentrations in synovial fluid varied from 36.3 to 103.0% of those in serum, with a mean value of 65.0 +/- 14.4%. There is a highly significant correlation between carprofen concentrations in the serum and the synovial fluid.