Determination of alternative ceftolozane/tazobactam dosing regimens for patients with infections due to Pseudomonas aeruginosa with MIC values between 4 and 32 mg/L

Background: Optimization of the antibiotics for patients with infections due to MDR Pseudomonas aeruginosa (MDR-PA) often requires consideration of alternate dose and infusion times that can be influenced by renal function. Objectives: We sought to identify ceftolozane/tazobactam dosing schemes that optimized the probability of target attainment (PTA) against infections due to MDR-PA with ceftolozane/tazobactam MICs between 4 and 32 mg/L across different categories of renal function. Methods: A prior validated ceftolozane/tazobactam population pharmacokinetic model was used for Monte Carlo simulation of 128 alternate permutations of dose, infusion time and renal function in 5000 cases/permutation. Four ceftolozane/tazobactam doses (250/125mg to 2/1 g) every 8 h with infusion durations of 1-7 h and as continuous infusions were simulated. The model simulated ceftolozane/tazobactam clearance as a function of creatinine clearance (CLCR) within four categories of estimated renal function: 15-29, 30-50, 51-120 and 121-180 mL/min. The PTA was benchmarked on 40% free ceftolozane/tazobactam concentration time above the MIC. Results: The 512 alternate scenarios identified the current ceftolozane/tazobactamdose of 1/0.5 g to be optimal for MICs <= 32 mg/L (CLCR 15-50 mL/min), <= 16 mg/L (CLCR 51-120 mL/min) and <= 8 mg/L (CLCR 121-180 mL/min). Extended infusion of 4-5 h had a higher PTA than shorter and continuous infusions in simulations of augmented renal clearance across infections with MICs of 4-32 mg/L. Conclusions: Extended infusion ceftolozane/tazobactam regimens should be investigated as a potential dosing solution to improve the PTA against infections due to MDR-PA with higher ceftolozane/tazobactam MICs.