Zerbaxa (ceftolozane and tazobactam) is a combination antibiotic used to treat certain bacterial infections of the lungs, stomach, or urinary tract. It may be given with another antibiotic. Ceftolozane kills bacteria by preventing them from forming their cell wall. Some bacteria produce beta-lactamases that reduce ceftolozane's effectiveness, but tazobactam, a beta-lactamase inhibitor, blocks these substances, allowing ceftolozane to continue working.