Effects of pirazolac on arachidonic acid metabolism in the human synovial system.

Six patients suffering from rheumatoid arthritis with massive knee joint effusions were treated with single daily doses of 600 mg pirazolac, a novel non-steroidal anti-inflammatory drug, for 3 days. Before the first dose, 3 hours after the second and the third dose, specimens of plasma and synovial fluid were drawn simultaneously. Plasma and synovial fluid concentrations of pirazolac, as determined by HPLC, amounted to 47.9 micrograms/ml and 19.8 micrograms/ml (Day 2) and 55.5 micrograms/ml and 18.7 micrograms/ml (Day 3), respectively. The samples were analyzed for PGE2, LTB4, LTC4 and LTD4 applying various extraction procedures and subsequent radioimmunoassays. PGE2 levels decreased during treatment from 928 pg/ml to 443 pg/ml after the third dose of pirazolac. LTB4 levels were slightly but insignificantly augmented. LTC4 and LTD4 concentrations were below the detection limit prior to and after administration of the drug.