Ibuprofen kinetics in plasma and synovial fluid of arthritic patients.

After administration of a single dose and at steady state, ibuprofen concentrations were measured simultaneously in plasma and synovial fluid obtained from eight patients with rheumatoid arthritis. By seven hours after a dose at steady state, the mean synovial fluid: plasma ibuprofen concentration ratios were constant, and the synovial fluid levels were, on average, greater than those in plasma. The extent to which ibuprofen was bound to protein was somewhat greater in plasma than in synovial fluid. As a result, the mean synovial fluid:plasma free concentration ratio for seven-hour and later specimens was greater than that based on total concentrations. The degree of accumulation of ibuprofen in each fluid was minimal, consistent with its short half-life.