Comparison of two enteric-coated acetylsalicylic acid preparations by monitoring steady-state levels of salicylic acid and its metabolites in plasma and urine.

In a randomized three-way crossover study, 12 healthy male volunteers were given multiple oral doses, i.e. 1.5 g b.i.d. for 7 days, of two different types of enteric-coated acetylsalicylic acid (ASA) preparations, one being a conventional enteric-coated tablet (ET) and the other enteric-coated granules (EG) in a capsule; conventional ASA tablets were used as a reference. Plasma levels and excretion of salicylic acid and some of its metabolites were investigated under steady-state conditions. Plasma salicylic acid (SA) and salicyluric acid (SUA) levels were determined using a liquid chromatographic method. Two separate analyses were done to quantitate the metabolites in urine. SA, SUA, and gentisic acid were each assayed by the method used for plasma. Total salicylate was also determined. There was no significant difference in urinary excretion of total salicylate between the three formulations. A diurnal variation in the excretion of SUA and SA in urine was found. The two enteric-coated formulations provided significantly higher morning plasma concentrations than the conventional aspirin. The AUC was found to be significantly higher for ET than for the other two formulations. EG gave more uniform plasma levels during the studied 12-h intervals and also less inter- and intra-individual variations than ET, indicating that a b.i.d. regimen may be suitable for EG.