Pharmacokinetics of amoxicillin

Amoxicillin, a new semisynthetic penicillin, was administered in 250-mg doses intravenously and orally to normal men. After intravenous doses, the mean alpha disposition constant was 3.994 hr^-1 and the mean beta disposition constant was 0.692 hr^-1 with a corresponding beta half-life of 1.05 hr. The serum clearance rate was 0.264 1.kg^-1 with a volume of distribution at steady state (Vd₈₈) of 0.311 1.kg^-1. The mean k_a of the oral dose was 1.08 hr^-1 with a lag time o f 0.34 hr. Calculation o f areas under individual oral and intravenous serum concentration-time curves indicated an absolute availability of the oral dose of 88.7% (range, 70.9 to 105.5). In comparison with ampicillin, amoxicillin is absorbed at a faster rate and more completely from the gastro-intestinal tract and has a larger Vd₃₃. The beta phase half-life and serum clearance rates o f the two antibiotics are similar.