Final answer:
The medication effective against fungi, protozoa, and bacteria is metronidazole, which is a nitroimidazole compound active against various protozoan pathogens and certain anaerobic bacteria.
Step-by-step explanation:
The medication that is effective against fungi, protozoa, and bacteria is metronidazole. Metronidazole belongs to the class of nitroimidazoles and exhibits activity against a variety of protozoan pathogens such as Giardia lamblia, Entamoeba histolytica, and Trichomonas vaginalis. It becomes activated in low-oxygen environments, leading to DNA strand breakage and interference with DNA replication in target cells. Although primarily known as an antibacterial, metronidazole's activity also extends to certain anaerobic bacteria and protozoa. This characteristic makes it a unique option among the provided choices as azithromycin, Diflucan (fluconazole), and cefazolin have more specific modes of action and are typically not effective against both bacteria and protozoa.