Antimicrobial Activity and Human Pharmacology of Amoxicillin

Abstract

The in vitro antibacterial activity of amoxicillin (α-arnino-p-hydroxybenzylpenicillin) against 568 clinical isolates was evaluated. Amoxicillin was active against gram-positive organisms at an inhibitory level similar to that of ampicillin or penicillin G. The majority of Streptococcus pyogenes, Diplococcus pneumoniae, and Streptococcus viridans were inhibited by 0.05 µg of amoxicillin/m1. Most Haemophilus infiuenzae and Neisseria gonorrhoeae were inhibited by 0.1 µg/ml. Amoxicillin and ampicillin were equally active against Escherichia coli and Proteus mirabilis. However, amoxicillin was twofold more active against Salmonella species than ampicillin but twofold less active against Shigella species. Enterococci were more susceptible to amoxicillin than to ampicillin. Amoxicillin produced peak serum levels that were two to two and a half times those produced with an identical amount of ampicillin. Blood levels of amoxicillin were still present 8 hr after administration of a single oral 500-mg dose. Absorption of amoxicillin was not decreased by food. Orally administered amoxicillin produced serum levels equal to levels produced by sodium ampicillin or ampicillin trihydrate administered im. The peak blood level achieved with a single oral 3-g dose of amoxicillin equaled that achieved with 3.5 g of ampicillin plus 1 g of probenecid or 4.8 × 10⁶ units of procaine penicillin plus 1 g of probenecid. Urinary excretion of amoxicillin was 50%–70%; this was significantly greater than the 30%–40% excretion of ampicillin.