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 g/ml and 9 clinical isolates of MRSA with MICs of 4 to 16 g/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 g/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 g/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 g/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 g/ml at doses of 750 mg TID and strains with MICs of <16 g/ml at doses of 1,500 mg TID.

Emerging Treatment Options for Infections by Multidrug-Resistant Gram-Positive Microorganisms

“…The inhibitory concentration value of tomopenem was also more than 15-fold lower than that of imipenem and meropenem [113]. In murine models of MRSA infection, tomopenem showed bactericidal effects against all nine strains of MRSA with MICs of ≤16 µg/mL [117]. The half-life of tomopenem was 0.197 h in sera and 0.343 h in the lungs and the percentage of the dosage interval in which the serum level exceeded the MIC (%T > MIC) for tomopenem was 16% in sera and 15% in the lungs [118].…”