Availability studies on acetylsalicylic acid, salicylamide and phenacetin at different pH values.

The optimum partitioning rate of acetylsalicylic acid has been attained at pH = 4 and minimum partitioning rate was found to be at pH = 8. The maximum partitioning rate of salicylamide was observed at pH = 5 and the smallest one was found at pH = 6 or 8. At pH = 3 a maximum amount of phenacetin was found in the aqueous phase, while at pH = 6 a maximum amount was found in the octanolic layer. The maximum partitioning rate was found at pH = 6 and lowest one was observed at pH = 3. The gastrointestinal absorption of acetylsalicylic acid, salicylamide and phenacetin was significantly increased, as reflected by the urinary excretion data in presence of solid buffer components at pH values of 4,5 and 6 respectively.