Which of the following antibiotics is known to have a combination with a salt?

Piperacillin-Tazobactam is a combination antibiotic that includes piperacillin, a broad-spectrum penicillin, and tazobactam, a β-lactamase inhibitor. This combination is specifically used to enhance the effectiveness of piperacillin against certain bacteria that produce β-lactamase enzymes, which can otherwise render penicillins ineffective.

The use of tazobactam, which is not an antibiotic by itself but instead helps protect piperacillin from degradation, helps in treating infections caused by resistant organisms. Therefore, this particular combination allows for broader coverage against a variety of gram-negative and some gram-positive bacteria.

In contrast, the other antibiotics listed do not come as a combination with a salt: Ciprofloxacin is a fluoroquinolone, Azithromycin is a macrolide, and Cephalexin is a first-generation cephalosporin. None of these have a co-formulated agent that serves to enhance their antibacterial spectrum in the same manner as piperacillin-tazobactam.