Correlation of aspirin excretion with parameters from different dissolution methods.

The cumulative urinary excretion of four different aspirin products (two tablets, a capsule, and a timed-release tablet) was determined in a crossover study using five subjects. Comparison of in vivo results showed a significant difference in cumulative urinary excretion levels at only 1 hr. The excretion from the two regular tablets was significantly different from the timed-release tablet, but the capsule showed no significant difference from the other three products. Each product was tested in the USP, Levy beaker, and the regular and large magnetic basket dissolution apparatus. Analysis of variance of the in vitro results showed a significant difference between the aspirin products and the dissolution methods at selected times. In vitro comparison with in vivo results for the four products showed that a regression analysis can be used to determined which dissolution methods produce a significant correlation with urinary excretion.