Availability of salicylate from salsalate and aspirin

Salicylate availability from salsalate (SSA) and aspirin (ASA) was examined in six rheumatoid arthritis patients in a multiple-dose double-blind crossover study. Doses contained equimolar amounts of salicylic acid. After initial ASA treatment to achieve therapeutic salicylate levels (150 to 300 micrograms/ml) the patients received equimolar doses of SSA or ASA. When steady state was achieved patients were hospitalized, and blood and urine specimens were obtained during three dosing intervals and during the washout period that followed. Thereafter, patients were placed on the alternate medication for at least a week and the in-hospital pattern was repeated. Despite insignificant differences in absorption of the formulations, as measured by urinary salicylate recovery, the plasma salicylic acid AUC was lower after SSA. Evidence indicates that this apparent lower availability of salicylate from SSA is due to incomplete hydrolysis to salicylic acid, the unhydrolyzed SSA being excreted mainly as glucuronide conjugates.