Comparison of In Vitro Susceptibility between 7:1 and 4:1 Mixtures of Amoxicillin and Clavulanate against Major Clinically-isolated Bacteria

Yi, Jongyoun; Lee, Jae Kyoo; Lee, Eun Joung; Kim, Eui Chong

Abstract

BACKGROUND: Amoxicillin/clavulanate (A/C) is a combination of a broad spectrum -lactam antibiotic amoxicillin and the potent -lactamase inhibitor clavulanate. A/C 7:1 combination is known to be equal in its clinical efficacy and to have less gastrointestinal adverse effects compared to conventional A/C 4:1 combination. We estimated in vitro antimicrobial activities of the 7:1 combination (AMOCLA Duo) and the conventional 4:1 combination against clinical bacterial isolates known to be the major causes of acute otitis media or sinusitis.
METHODS
Total 183 strains isolated from clinical specimens of patients at Seoul National University Hospital were tested for minimal inhibitory concentraion (MIC). Streptococcus pneumoniae and Haemophilus influenzae were tested by microdilution broth method and other bacterial species by agar dilution method according to the recommendations of National Committee for Clinical Laboratory Standards (NCCLS).
RESULTS
AMOCLA Duo was compared with the 4:1 combination in respect to MIC50, MIC90 and MIC range. For total 183 strains (30 methicillin-susceptible Staphylococcus aureus, 30 methicillin-sus-ceptible Staphylococcus epidermidis, 25 penicillin-susceptible S. pneumoniae, 42 penicillin-resistant S. pneumoniae, 33 H. influenzae and 23 Moraxella catarrhalis), mean MICs did not show statistically significant difference between the 2 combinations but they did for H. influenzae and M. catarrhalis.
CONCLUSIONS
As for the total test strains, in vitro antimicrobial activity of AMOCLA Duo was equal to that of the conventional 4:1 combination. For each species, H. influenzae and M. catarrhalis showed significant difference between mean MICs of the 2 combinations but other species did not. We do not suppose, however, that in case of H. influenzae this difference is of practical and clinical significance according to the NCCLS interpretive criteria for MIC. Although M. catarrhalis showed statistically very significant difference of MICs, this difference can be clinically solved due to the higher dose of amoxicillin in AMOCLA Duo.