Acetylsalicylic acid metabolites in blood and urine after plain and enteric-coated tablets.

Acetylsalicylic acid (ASA) was administered orally as a single dose to 7 healthy male volunteers as plain or enteric-coated (Entrophen) tablets using a crossover design. Blood and urine samples were collected and analysed for ASA metabolites by high performance liquid chromatography. Labile and stable glucuronide conjugates of salicylic acid (SA) were measured in urine after differential hydrolysis with glucuronidase. Plasma kinetic parameters for the ASA metabolites SA and salicyluric acid were not different for the 2 formulations, apart from the delayed appearance after the enteric-coated tablets. Total urinary recovery, and recovery of salicyluric acid and the two SA glucuronides were not different, thus confirming the equivalent bioavailability and metabolite profile of the 2 ASA formulations.