In vitro and in vivo antibacterial activities of a new injectable carbapenem, S-4661, against gynaecological pathogens

Carbapenems are often used to treat infections in obstetrics and gynaecology because of their activity against anaerobes. S-4661, a new injectable carbapenem antibiotic, has favourable pharmacokinetic properties and is not hydrolysed by dehydropeptidase I. We investigated the in vitro and in vivo antibacterial activities of S-4661 against strains of Streptococcus agalactiae, Escherichia coli, Peptostreptococcus magnus, Bacteroides fragilis and Prevotella bivia, which are major pathogens in the fields of obstetrics and gynaecology. The MIC50 and MIC90 of S-4661 for these strains were 0.25 and 1 mg/L, respectively. The in vivo efficacy of S-4661 was evaluated in a rat model of intrauterine infection, namely pyometra caused by E. coli and B. fragilis. The accumulation of neutrophils in the uterus in the S-4661-treated group was less marked and the number of bacteria significantly lower than those in the untreated group. These results suggest that S-4661 may be useful for treating polymicrobial infections in the fields of obstetrics and gynaecology.