The study's primary objective is to determine plasma and dialysis fluid concentrations in patients prescribed ceftazidime-avibactam as the standard treatment for their infection and requiring continuous venovenous hemodiafiltration (CVVHDF) as part of the standard treatment for acute or chronic renal failure. Secondarily, the study will evaluate the pharmacokinetics of ceftazidime-avibactam in these patients on CVVHDF. The study will also determine if the prescribed dose meets pharmacodynamic targets.