Comparative in vitro potency of amoxycillin–clavulanic acid and four oral agents against recent North American clinical isolates from a global surveillance study

The in vitro activity of amoxycillin–clavulanic acid was compared with four comparator oral antimicrobial agents; ampicillin, azithromycin, cefuroxime and trimethoprim–sulphamethoxazole against 4536 recent clinical isolates covering 29 species isolated in the US and Canada between 1997 and 1999. Based upon Minimum inhibitory concentrations (MICs), amoxycillin–clavulanic acid was the most active agent against many Gram-positive species and phenotypes including methicillin susceptible Staphylococcus aureus (MSSA) Staphylococcus epidermidis, Enterococcus faecalis, Streptococcus pyogenes, Streptococcus pneumoniae including penicillin intermediate and macrolide resistant strains and was as active as ampicillin against Streptococcus agalactiae, penicillin resistant S. pneumoniae and viridans streptococci. Against Enterobacteriaceae amoxycillin–clavulanic acid in general, displayed weak activity with only Proteus mirabilis and Proteus vulgaris displaying levels of susceptibility above the 90th percentile. Amoxycillin–clavulanic acid had significant activity against many species of Gram-negative non-Enterobacteriaceae including Haemophilus influenzae, Haemophilus parainfluenzae and Moraxella catarrhalis but negligible activity against Burkholderia cepacia, Pseudomonas aeruginosa and Stenotrophomonas maltophilia. Amoxycillin–clavulanic acid continues to retain excellent activity against the majority of targeted pathogens despite 20 years of clinical use.