cCeftolozane is a new cephalosporin with activity against Gram-negative and Gram-positive microorganisms. However, the compound is susceptible to degradation by extended-spectrum beta-lactamases (ESBLs). Tazobactam is an ESBL inhibitor and is combined with ceftolozane to broaden its activity. Surprisingly, although tazobactam has been available for over 20 years, few if any reliable data exist on the tazobactam pharmacokinetic (PK) properties in mice. To evaluate the PK and pharmacodynamic (PD) relationships in mice, the PK properties of tazobactam and ceftolozane were extensively investigated. Thigh-infected neutropenic CD-1 mice were injected intraperitoneally with a single 0.1-ml dose containing ceftolozane, tazobactam, or both compounds. Ceftolozane was applied in 2-fold-increasing doses of 4 mg/kg of body weight to 64 mg/kg alone or in combination. Tazobactam was combined in reverse doses (thus, 64/4 mg/kg, 32/8 mg/kg, etc.) (n ؍ 2 per time point). In separate validation experiments, ceftolozane-tazobactam was given alone or in combination at 32/8 mg/kg and 8/32 mg/kg (n ؍ 4 per time point). Plasma samples (one per mouse) and bronchoalveolar lavage samples were collected at up to 12 time points until 6 h after administration. There were no significant differences in the ceftolozane and tazobactam PK alone versus combined, indicating no PK interaction. The PKs were linear and dose proportional for both compounds and showed a good penetration in the epithelial lining fluid. The estimated mean (standard deviation) half-life of ceftolozane was 0.287 h (0.031 h), and that of tazobactam was 0.176 h (0.026), and the V was 0.43 liter/kg and 1.14 liter/kg, respectively. The estimates of tazobactam parameters can also be used to (re)interpret PD data.
Ceftolozane is a novel cephalosporin with activity against Pseudomonas aeruginosa and other Gram-negative microorganisms. However, the compound is susceptible to degradation by extended-spectrum beta-lactamases (ESBLs); therefore, the compound is combined with tazobactam, a potent beta-lactamase inhibitor, to broaden its activity. The combination had been shown to be active in vitro against a wide variety of microorganisms with different resistance mechanisms (1-5). The combination has also been shown to be active in vivo, in particular in animal models, against both P. aeruginosa and Enterobacteriaceae (6, 7). However, the pharmacodynamics of tazobactam in vivo have not been fully identified, despite being available for over 20 years in the combination piperacillin-tazobactam. Indeed few, if any, reliable data exist on the tazobactam pharmacokinetic (PK) properties in mice, including its penetration in lung epithelial lining fluid (ELF), precluding pharmacodynamic analyses. In addition, it is not clear whether pharmacokinetic interactions exist between cephalosporins and tazobactam. In one earlier, limited study, such a pharmacokinetic interaction was observed between these two compounds (8) in mice, although it was not observed in men (9). Thus, the primary object...