The disposition of biphenylacetic acid following topical application.

Plasma and synovial fluid concentrations of biphenylacetic acid were determined following application of 3 g of 3% biphenylacetic acid gel to one knee of patients suffering from rheumatoid arthritis. The mean peak plasma concentration was 34 ng/ml. Synovial fluid concentrations tended to follow plasma concentrations but at a somewhat lower level, the mean peak synovial fluid concentration was 21 ng/ml. The average ratio of synovial fluid AUC (0-24 h) to plasma AUC (0-24 h) was 0.58, r = 0.97. Where patients had bilateral effusions, the concentration in the ipsilateral knee at each time point examined was not significantly different to that in the contralateral knee, suggesting that absorption was initially into the plasma and subsequently into the synovium.