title: Efficacy of human-simulated exposures of tomopenem (formerly CS-023) in a murine model of Pseudomonas aeruginosa and methicillin-resistant Staphylococcus aureus infection.
abstract: Tomopenem (formerly CS-023) is a novel carbapenem with improved activity against diverse hospital pathogens, including Pseudomonas aeruginosa and methicillin-resistant Staphylococcus aureus (MRSA), and has a half-life about twice longer than the half-lives of other carbapenems such as imipenem and meropenem. Our objective in this study was to estimate the efficacy of tomopenem in humans by human-simulated exposures in a neutropenic murine thigh infection model against 9 clinical isolates of P. aeruginosa with MICs of 4 to 32 μg/ml and 9 clinical isolates of MRSA with MICs of 4 to 16 μg/ml. Human-simulated dosing regimens in neutropenic mice were designed to approximate the cumulative percentage of a 24-h period that the free drug concentration exceeds the MIC under steady-state pharmacokinetic conditions (f%T(MIC)) observed with tomopenem at 750 and 1,500 mg given as a 0.5-h infusion three times a day (TID) in humans. As reported previously, there was no difference between the target values of P. aeruginosa and MRSA required for efficacy (K. Sugihara et al., Antimicrob. Agents Chemother. 54:5298-5302, 2010). Tomopenem at 750 mg showed bactericidal or bacteriostatic effects against 10 of 11 strains of P. aeruginosa and MRSA with MICs of ≤ 8 μg/ml (f%T(MIC) ≥ 41), and tomopenem at 1,500 mg showed bactericidal effects against 16 of 17 strains of P. aeruginosa and MRSA with MICs of ≤ 16 μg/ml (f%T(MIC) ≥ 43). Meropenem at 1,000 mg TID was tested for comparison purposes and showed bactericidal or bacteriostatic effects against 3 of 4 strains of P. aeruginosa with MICs of ≤ 4 μg/ml (f%T(MIC) ≥ 33). From these results, tomopenem is expected to be effective with an f%T(MIC) of over 40 against P. aeruginosa and MRSA strains with MICs of ≤ 8 μg/ml at doses of 750 mg TID and strains with MICs of ≤ 16 μg/ml at doses of 1,500 mg TID.
authors.affiliation: Biologics Research Laboratories, Daiichi Sankyo Co Ltd, Edogawa-ku, Tokyo 134-8630, Japan. sugihara.kiyoshi.mv@daiichisankyo.co.jp
authors.forename: Kiyoshi
authors.initials: K
authors.lastname: Sugihara
authors.forename: Kazuhiro
authors.initials: K
authors.lastname: Tateda
authors.forename: Naotoshi
authors.initials: N
authors.lastname: Yamamura
authors.forename: Tetsufumi
authors.initials: T
authors.lastname: Koga
authors.forename: Chika
authors.initials: C
authors.lastname: Sugihara
authors.forename: Keizo
authors.initials: K
authors.lastname: Yamaguchi
mesh_terms: D000818:Animals; D015780:Carbapenems / Q000493:pharmacokinetics / Q000627:therapeutic use*; D006801:Humans; D008297:Male; D055624:Methicillin-Resistant Staphylococcus aureus / Q000187:drug effects* / Q000472:pathogenicity*; D051379:Mice; D008813:Mice, Inbred ICR; D011552:Pseudomonas Infections / Q000188:drug therapy*; D011550:Pseudomonas aeruginosa / Q000187:drug effects* / Q000472:pathogenicity*; D013203:Staphylococcal Infections / Q000188:drug therapy*
chemical_list: D015780:Carbapenems; C492232:tomopenem