Pharmacokinetics of fosfosal in rats and dogs

Fosfosal (Disdolen) is a non acetyl derivative of salicylic acid with antiinflammatory and analgesic properties and a greater tolerance than acetylsalicylic acid and lysine acetylsalicylate. In the present work the pharmacokinetics of fosfosal have been studied after oral and intravenous administrations of 100 and 80 mg/kg in rats and dogs, respectively. Plasma concentrations of fosfosal and salicylic acid were determined by an HPLC method. After intravenous administration fosfosal plasma levels decreased rapidly showing a half-life of 2.7 min in rats and 6.7 min in dogs. Fosfosal in plasma is quickly hydrolyzed into salicylic acid producing high concentrations in few minutes after administration. The half-life of salicylic acid was 13.8 and 7.1 h for rats and dogs, respectively. After oral administration only salicylic acid was detected in plasma, indicating that fosfosal, when orally administered, behaves as a prodrug. From the comparison of the AUC for salicylic acid obtained after oral and intravenous administrations it can be deduced that fosfosal it totally absorbed in the two species studied.