The effect of antacid on aspirin pharmacokinetics in healthy Thai volunteers.

The effect of antacid on aspirin pharmacokinetics and bioavailability was determined in 10 healthy adult male and female volunteers, aged 20-45 years old. Each subject received 650 mg of aspirin orally after an overnight fast. The wash out period was 14 days and then all subjects were given 650 mg of aspirin 10 minutes after antacid (aluminium hydroxide and magnesium hydroxide). Plasma aspirin, salicylate and salicyluric acid levels were determined by a specific high performance liquid chromatographic analysis. Individual plasma profiles were analysed using compartmental and non-compartmental methods. The results show that antacid affected the relative bioavailability of aspirin since the mean peak concentration (Cmax) of aspirin was significantly higher when antacid was given. However, the time to reach peak concentration (Tmax) and the area under the plasma concentration-time curve (AUC) showed no significant difference between the two treatments. It was, therefore, not possible to conclude that the non-bioequivalence was caused by a difference in rate or amount of aspirin absorption, or both. No significant difference was observed in Cmax, Tmax, AUC, t1/2, Ka, Kel of salicylate and salicyluric acid. However, the rate of total salicylate absorption was increased since the absorption rate constant (Ka) was higher when antacid was given. This may provide a more rapid effect of the drug.