Naproxen concentrations in serum, synovial fluid, and synovium.

Naproxen levels in serum, synovial fluid and synovium of eighteen patients with "classical" or "definite" rheumatoid arthritis and chronic knee effusion were studied. After oral administration of 250 mg naproxen twice daily, naproxen levels in synovial fluid were found to be more than half as high as in serum. Even in synovium itself naproxen levels were appreciable.