Comparative bioavailability of aspirin from buffered, enteric-coated and plain preparations

The bioavailability and pharmacokinetics of acetylsalicylic acid were studied in 6 volunteers, under a cross-over design, using plain compressed aspirin, two buffered preparations and an enteric-coated tablet. Absorption, calculated from urinary excretion, was complete for all the formulations. The buffered forms gave higher peak concentrations and AUC for acetylsalicylic acid than the other forms. Absorption from the enteric-coated tablet was the slowest. Acetylsalicylic acid was not measurable in plasma (less than 0.1 micrograms/ml) at any time in 3 subjects after plain and in 2 after enteric-coated aspirin. Acetylsalicylic acid was no longer measurable in plasma after 4 hours, irrespective of the preparation given.