What it is
Bacitracin is a mixture of ring-shaped peptides made by a bacterium. The prescription eye-ointment label describes bacitracin zinc as the zinc salt of "a mixture of related cyclic polypeptides (mainly bacitracin A) produced by the growth of an organism of the licheniformis group of Bacillus subtilis var Tracy."
Its main component, bacitracin A, is described by ChEBI (via PubChem) as a homodetic cyclic peptide: a first unit carrying a thiazoline ring, attached to leucine, D-glutamate, lysine, D-ornithine, isoleucine, D-phenylalanine, histidine, D-aspartate and asparagine. The ring is closed from the side chain of lysine to the last amino acid, so the molecule is a loop with a short tail. PubChem gives C66H103N17O16S, molecular weight 1,422.7 (CID 10909430). Several of the residues are D-forms, the mirror images of the amino acids human proteins use.
Because it is a natural mixture, bacitracin's strength is measured in units of activity, not milligrams: the eye-ointment label requires not less than 40 units per milligram.
What it does
The prescription eye-ointment label states that bacitracin "is active against most gram-positive bacilli and cocci including hemolytic streptococci," which is why combination products pair it with polymyxin B, an antibiotic for Gram-negative bacteria.
Three regulatory lives
| Form | US status | Basis |
|---|---|---|
| First-aid ointment (bacitracin or bacitracin zinc, 500 units/g) | Over the counter | Monograph, 21 CFR 333.110; labelling fixed by 333.150; 356 OTC labels list bacitracin in openFDA |
| Eye ointments (with polymyxin B; some also with neomycin and hydrocortisone) | Prescription | Generic applications, e.g. Bausch & Lomb ANDA 064046 (1995); 4 prescription ophthalmic products listed |
| Intramuscular injection (10,000 and 50,000 units/vial) | Withdrawn | FDA request 2020-01-31; safety-or-effectiveness determination 2022-09-15 (87 FR 56680) |
The over-the-counter status deserves a plain reading: a monograph is a rule listing permitted ingredients, strengths and label wording. The first-aid claim the rule allows — "first aid to help prevent infection in minor cuts, scrapes, and burns", in permitted variants — rests on the rulemaking record cited in the CFR (1987–1999), not on a modern placebo-controlled trial reported on the label.
The injection: approved in 1948, withdrawn in 2020
The Federal Register notice of 2022-09-15 (87 FR 56680) sets out the record:
- 1948-07-29: bacitracin for injection first approved (originally NDA 6-483, later ANDA 060733, last held by Pharmacia and Upjohn, a Pfizer subsidiary), for intramuscular use limited to infants with staphylococcal pneumonia and empyema.
- 1984: the Anti-Infective Drugs Advisory Committee concluded intramuscular bacitracin was not safe and effective.
- April 2019: the Antimicrobial Drugs Advisory Committee advised that its benefits did not outweigh its risks for that one indication.
- 2020-01-31: citing nephrotoxicity and anaphylactic reactions, FDA asked every holder to request withdrawal; Pfizer, Akorn, Mylan, X-Gen and Fresenius Kabi did so on 5–7 February 2020.
- 2022-09-15: FDA determined the injection was withdrawn for reasons of safety or effectiveness and will not accept or approve generic versions.
The notice adds that clinicians had generally stopped using it because other approved treatments without these risks were available.
Safety
For the ointments, the warnings are fixed by the monograph (21 CFR 333.150): external use only, not in the eyes or over large areas of the body; a doctor for deep or puncture wounds, animal bites or serious burns; stopping and seeing a doctor if the condition persists or worsens or if a rash or other allergic reaction develops; not for people allergic to any ingredient; and no longer than one week unless a doctor directs it. The kidney toxicity and anaphylaxis that ended the injection were named for the injected form (87 FR 56680); the opened records do not report them for the labelled topical use.
Where it stands
- Over the counter as a first-aid antibiotic ointment under 21 CFR part 333.
- Prescription in eye ointments combined with polymyxin B.
- Injection withdrawn (FDA request 2020; determination 2022, 87 FR 56680).
- Research record: PubMed indexes 5,006 records, 139 tagged as randomised trials (2026-10-11).
Related reading
Bacitracin is one of several antibiotics that are peptides at heart: vancomycin is a glycopeptide used in hospitals, and daptomycin a ring-shaped lipopeptide. The bacterial wall many of these drugs target is described under the bacterial wall polymer peptidoglycan, and the body's own antimicrobial peptide in the LL-37 entry.