[Pharmacokinetic studies following 2 and 4-week Felbinac gel administration to the knee joint].

Twelve patients with osteoarthrosis were locally treated with Felbinac Gel (biphenyl acetic acid (BPAA) 3%) three times daily for 14 days (five patients), 28 days (six patients) or 42 days (one patient) before elective knee joint surgery. BPAA plasma concentrations as of the seventh day of treatment were steady at between 423 and 1040 ng/ml. In surgery, synovial and tissue samples were taken to determine BPAA concentrations. Moderate and sometimes higher synovial BPAA levels in the treated knee joint compared to the contralateral knee seem to indicate a combined direct and systemic absorption. The highest BPAA concentrations (1497-13939 ng/g) were measured in the skin. Drug levels in the synovial membrane (36-994 ng/g), the synovia (104-768 ng/ml), tendon (less than 10-197 ng/g), cartilage (less than 10-109 ng/g), muscle (12-101 ng/g), and subcutis (16-97 ng/g) were lower. BPAA neither accumulates in the skin, nor in any other peri-articular tissue. A steady state was reached as of the 14th day of treatment at the latest. None of the patients reported any local or systemic side effects.