Assessment of aspirin absorption rate from urinary excretion rate measurements

It is shown on the basis of pharmacokinetic simulations and experimental data that adequate evaluation of aspirin dosage forms with different absorption rates by urinary excretion measurements in man requires that such measurements be made during the first hour after drug administration. Measurements made only after 3 hours are totally inadequate for that purpose. An assessment of the completeness of absorption obviously does not require serial measurements but needs only a determination of the total amount excreted.