tomopenem and Staphylococcal-Infections

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.

Topics: Animals; Carbapenems; Humans; Male; Methicillin-Resistant Staphylococcus aureus; Mice; Mice, Inbred ICR; Pseudomonas aeruginosa; Pseudomonas Infections; Staphylococcal Infections

Tomopenem (formerly CS-023) is a novel carbapenem with broad-spectrum activities against diverse hospital pathogens, including Pseudomonas aeruginosa and methicillin-resistant Staphylococcus aureus (MRSA). We examined the in vivo pharmacodynamic characteristics of tomopenem against P. aeruginosa and MRSA by using a neutropenic murine thigh infection model with P. aeruginosa 12467 (MIC, 1 μg/ml) and MRSA 12372 (MIC, 2 μg/ml). The mice had 10(6) to 10(7) CFU/thigh of each strain 2 h after inoculation and were treated for 24 h with a fractionated administration of tomopenem given at intervals of 3, 6, 12, and 24 h. The serum protein binding of tomopenem was 17.4%. The efficacy of tomopenem in both infection models was enhanced by frequent dosing, which indicates that the efficacy is driven by the time above MIC (T(MIC)). In a sigmoid model, the cumulative percentages of the 24-h period that the concentrations of free, unbound fractions of the drug exceeded the MIC under steady-state pharmacokinetic conditions (f%T(MIC)s) were best correlated with efficacy when R(2) was 0.79 and 0.86 against P. aeruginosa and MRSA, respectively. Other pharmacokinetic and pharmacodynamic (PK-PD) indexes for the free, unbound fractions, the area under the concentration-time curve over 24 h in the steady state divided by the MIC (AUC/MIC) and the maximum concentration of the drug in serum divided by the MIC (C(max)/MIC), showed poor correlation with efficacy when R(2) was ≤0.42. The f%T(MIC) values required for a static effect, 1-log kill, and 2-log kill against P. aeruginosa were 29, 39, and 51, respectively, which were similar to those for meropenem, for which the values were 24, 33, and 45, respectively. Against MRSA, the values for tomopenem were 27, 35, and 47. In conclusion, the pharmacodynamic characteristics of tomopenem were similar to those of meropenem against P. aeruginosa, and there was no difference between the target values for P. aeruginosa and MRSA required for efficacy in this study.

Topics: Animals; Anti-Bacterial Agents; Carbapenems; Male; Methicillin-Resistant Staphylococcus aureus; Mice; Mice, Inbred ICR; Pseudomonas aeruginosa; Pseudomonas Infections; Staphylococcal Infections; Thigh