A validated LC-MS/MS method for the simultaneous quantification of the novel combination antibiotic, ceftolozane-tazobactam, in plasma (total and unbound), CSF, urine and renal replacement therapy effluent: application to pilot pharmacokinetic studies.

Abstract

Novel treatment options for some carbapenem-resistant Gram-negative pathogens have been identified by the World Health Organization as being of the highest priority. Ceftolozane-tazobactam is a novel cephalosporin-beta-lactamase inhibitor combination antibiotic with potent bactericidal activity against the most difficult-to-treat multi-drug resistant and extensively drug resistant Gram-negative pathogens. This study aimed to develop and validate a liquid chromatography- tandem mass spectrometry method for the simultaneous quantification of ceftolozane and tazobactam in plasma (total and unbound), renal replacement therapy effluent (RRTE), cerebrospinal fluid (CSF) and urine. Analytes were separated using mixed-mode chromatography with an intrinsically base-deactivated C18 column and a gradient mobile phase consisting of 0.1% formic acid, 10mM ammonium formate and acetonitrile. The analytes and internal standards were detected using rapid ionisation switching between positive and negative modes with simultaneous selected reaction monitoring. A quadratic calibration was obtained for plasma (total and unbound), RRTE and CSF over the concentration range of 1-200mg/L for ceftolozane and 0.5-100mg/L for tazobactam, and for urine the concentration range of 10-2,000mg/L for ceftolozane and 5-1,000mg/L for tazobactam. For both ceftolozane and tazobactam, validation testing for matrix effects, precision and accuracy, specificity and stability were all within the acceptance criteria of ±15%. This methodology was successfully applied to one pilot pharmacokinetic study in infected critically ill patients, including patients receiving renal replacement therapy, and one case study of a patient with ventriculitis, where all patients received ceftolozane-tazobactam.