Pharmacokinetics of amoxycillin in elderly in-patients

The pharmacokinetics of amoxycillin (500 mg) given by intravenous injection and as two oral formulations on three consecutive days were investigated in eight frail elderly in-patients. Marked interindividual variation was found in all kinetic parameters after intravenous injection. The area under the curve (AUC) ranged from 32 to 155 mg.l-1.h and the distribution volume ranged from 13 to 37.1. The mean plasma clearance was 109 ml/min (range 53 to 255 ml/min). Elimination half-life ranged from 1.6 to 3.0 h (mean 2.4 h). The absolute bioavailability after oral administration was highly variable and ranged from 24 to 86% (mean 55%). The bioavailability of the two formulations was not significantly different. The performance of a pharmacokinetic study in these patients was very difficult, regarding their inability to tolerate an intravenous infusion, incontinence, disruption of everyday routine and problems with drinking the required volume of water.