Bacitracins are branched, cyclic, decapeptide antibiotics. Bacitracin A is the most active of the group and the main component of the commercial bacitracin preparations that are used either topically or PO. These antibiotics are bactericidal. They interfere with cell membrane function, suppress cell wall formation by preventing the formation of peptidoglycan strands, and inhibit protein synthesis. Bactericidal activity requires the presence of divalent cations, such as zinc.
The spectrum of bacitracins is similar to that of penicillin G and is mostly limited to gram-positive and a few gram-negative bacteria, as well as some spirochetes. Most gram-negative organisms are not susceptible, probably due to lack of penetration of the drug through the outer membrane. Resistance is rare. Bacitracins are often used in combination with neomycin and polymyxins to enhance the antibacterial spectrum.
Bacitracins are not appreciably absorbed from the GI tract and are not used systemically because of their pronounced nephrotoxicity. However, they are used locally in wound powders and ointments, dermatologic preparations, eye and ear ointments, and as feed additives in swine and poultry rations for growth promotion. In antibiotic-associated pseudomembranous colitis caused by Clostridium difficile cytotoxin, bacitracin (given PO) is considered an alternative to vancomycin. Hypersensitivity reactions to bacitracins are seen occasionally.
Last full review/revision March 2012 by Dawn Merton Boothe, DVM, PhD, DACVIM, DACVCP