Samples of blood and joint fluid, from 60 patients who had taken an aspirin compound, were examined for salicylates. The earliest appearance of salicylates occurred in blood between 3 and 13 minutes after intake, and in joint fluid between 11 and 36 minutes. Salicylates attained maximum concentration in joint fluid 100 to 155 minutes after intake. Simultaneous concentrations of salicylates (near peak level) in blood and joint fluid were invariably lower in the latter. Acetylsalicylate level in blood averaged 54% of the total salicylates ingested and decreased to 0 within 75 minutes after intake. Joint fluid contained a similar proportion of acetylsalicylate, but deacetylation progressed more slowly.
Soren A. Transport of Salicylates From Blood to Joint Fluid. Arch Intern Med. 1973;132(5):668-672. doi:10.1001/archinte.1973.03650110024005