Treating infections with ceftolozane/tazobactam in subjects having impaired renal function

A method of treating an infection in a patient having an estimated creatinine clearance of up to about 50 mL/min, comprising administering to the patient in need thereof a dose of ceftolozane and tazobactam in a 2:1 weight ratio between ceftolozane active and tazobactam active, on two or more successive days of treatment, in amounts and at a dosing interval effective to provide at least an unbound concentration of ceftolozane of at least 8 micrograms/mL for at least 30% of the time between successive treatment days and unbound tazobactam of about 1 microgram/mL for at least 20% of the time and about 0.5 microgram/mL for about or higher than 50% of the time.