Ceftolozane/tazobactam dose regimens in severely/morbidly obese patients with complicated intra-abdominal infection or complicated urinary tract infection

Ceftolozane/tazobactam is approved for treatment of complicated intra-abdominal infection (cIAI) and complicated urinary tract infection (cUTI) with renal function-based dose adjustment. Given that creatinine clearance, body weight and sex are highly correlated in severely/morbidly obese patients, this study investigated whether approved dosing regimens for ceftolozane/tazobactam are appropriate in severely/morbidly obese patients based on simulated pharmacokinetic/pharmacodynamic target attainment, with confirmation from observed clinical outcomes data from the phase 3 clinical development programme. Using a previously published population pharmacokinetic model, 1000 patients were randomly sampled from an internal pooled database of 201 severely/morbidly obese patients (BMI ≥ 35 kg/m2) and were used for Monte Carlo simulation to test whether the labelled dose regimens can achieve ≥90% probability of a target of 32.2% (1-log kill) time above free ceftolozane concentration against pathogens at an MIC up to 8 mg/L. Clinical outcomes data for severely/morbidly obese patients with cIAI or cUTI from pivotal phase 3 studies were summarised to calculate clinical and composite cure rates as a complimentary support. With the approved renal function-based dosing regimens, >90% target attainment of bactericidal activity was achieved at MICs up to 8 mg/L in the simulated severely/morbidly obese patients with cIAI or cUTI, similar to target attainment in non-obese patients and further confirmed by phase 3 outcomes where cure rates in severely/morbidly obese patients and non-obese patients are similar. Approved dosing regimens of ceftolozane/tazobactam, adjusted according to renal function, can achieve adequate target attainment and high clinical cure rates in severely/morbidly obese patients with cIAI or cUTI.