Sequence effect on ampicillin blood levels noted in an amoxicillin, ampicillin, and epicillin triple crossover study.

Amoxicillin, ampicillin, and epicillin (500 mg of each) were given orally to fasting men and women in a triple crossover study. Peak serum concentrations were significantly higher for amoxicillin than for ampicillin and significantly lowest for epicillin. The concentrations of antibiotics in serum were comparable in men and women. Total urine recovery was highest for amoxicillin (56.7%) and lowest for epicillin (27.5%), and higher in men than in women for each of the three antibiotics. Saliva, sweat, and tears contained only very small amounts of amoxicillin and, rarely, ampicillin or epicillin. A significant (P < 0.02) sequence effect was noted in that peak serum concentrations of ampicillin were higher (6.4 mug/ml) if epicillin had been taken the previous week than when ampicillin was taken first (2.7 mug/ml).