Chloramphenicol is a broad-spectrum antibiotic that was first isolated from Streptomyces venezuelae in 1947. The drug was subsequently chemically synthesized. It has both a bacteriostatic and bactericidal effect; in the usual therapeutic concentrations it is bacteriostatic. Chloramphenicol is used for the treatment of serious gram-negative, gram-positive, and anaerobic infections. It is especially useful in the treatment of meningitis, typhoid fever, and cystic fibrosis. It should be reserved for infections for which other drugs are ineffective or contraindicated. Chloramphenicol, a small inhibitor of bacterial protein synthesis, is active against a variety of bacteria and readily enters the CSF. It has been used extensively in the last decades for the treatment of bacterial meningitis. In industrialized countries, chloramphenicol is restricted mostly to topical uses because of the risk of induction of aplastic anemia. However, it remains a valuable reserve antibiotic for patients with allergy to β-lactam antibiotics or with CNS infections caused by multiresistant pathogens.

Metronidazole was synthesized by France's Rhone-Poulenc laboratories and introduced in the mid-1950s under the brand name Flagel in the US, while Sanofi-Aventis markets metronidazole globally under the same trade name, Flagyl, and also by various generic manufacturers. Metronidazole is one of the rare examples of a drug developed as ant parasitic, which has since gained broad use as an antibacterial agent. Metronidazole, a nitroimidazole, exerts antibacterial effects in an anaerobic environment against most obligate anaerobes. Metronidazole is indicated for the treatment of the following infections due to susceptible strains of sensitive organisms: Trichomoniasis: symptomatic, asymptomatic, asymptomatic consorts; Amebiasis: acute intestinal amebiasis (amebic dysentery) and amebic liver abscess; Anaerobic bacterial infections; Intra-abdominal infections, including peritonitis, intra-abdominal abscess, and liver abscess; Skin and skin structure infections; Gynecologic infections, including endometritis, endomyometritis, tubo-ovarian abscess, and postsurgical vaginal cuff infection; Bacterial septicemia; Bone and joint infections, as adjunctive therapy; Central Nervous System infections, including meningitis and brain abscess; Lower Respiratory Tract infections, including pneumonia, empyema, and lung abscess; Endocarditis. Metronidazole is NOT effective for infections caused by aerobic bacteria that can survive in the presence of oxygen. Metronidazole is only effective against anaerobic bacterial infections because the presence of oxygen will inhibit the nitrogen-reduction process that is crucial to the drug's mechanism of action. Once metronidazole enters the organism by passive diffusion and activated in the cytoplasm of susceptible anaerobic bacteria, it is reduced; this process includes intracellular electron transport proteins such as ferredoxin, transfer of an electron to the nitro group of the metronidazole, and formation of a short-lived nitroso free radical. Because of this alteration of the metronidazole molecule, a concentration gradient is created and maintained which promotes the drug’s intracellular transport. The reduced form of metronidazole and free radicals can interact with DNA leading to inhibition of DNA synthesis and DNA degradation leading to death of the bacteria. The precise mechanism of action of metronidazole is unknown. Metronidazole has a limited spectrum of activity that encompasses various protozoans and most Gram-negative and Gram-positive anaerobic bacteria. Metronidazole has activity against protozoans like Entamoeba histolytica, Giardia lamblia and Trichomonas vaginalis, for which the drug was first approved as an effective treatment.

Dimetridazole is an anti-fungal and anti-protozoal drug traditionally used in veterinary for the prevention and treatment of histomoniasis in turkeys, genital trichomoniasis in cattle and hemorrhagic enteritis in pigs. Results from the in vitro and in vivo tests suggested, that dimetridazole was not genotoxic compound, but its use is legally limited, although this compound is still can be found in eggs.