Constant blood withdrawal method for area under plasma concentration-time curve.

The area under the plasma concentration-time curve (AUC) was measured after an intravenous injection of sodium salicylate and after intragastric administration of aspirin, using either an intermittent sampling and the trapezoid rule (AUC-trapezoid) or the recently introduced constant blood withdrawal method (AUC-integrated concentration). Six dogs were used in each study. The AUC-integrated concentration was significantly higher than the AUC-trapezoid. The difference between the two methods was more significant after the intravenous infusion than after the intragastric administration. The higher AUC-integrated concentration was attributed to the inclusion of the initial plasma levels, which is an inherent advantage of the constant blood withdrawal method.