Bacitracin

Bacitracin, produced by Bacillus licheniformis, forms a metal-dependent complex (typically with zinc) around C55-isoprenyl pyrophosphate, the lipid carrier that shuttles peptidoglycan precursors from the cytoplasm to the growing cell wall. By preventing the pyrophosphatase step that regenerates the monophosphate carrier, it starves cell wall synthesis of its transport machinery. This target is upstream of and distinct from the D-Ala-D-Ala site of vancomycin, so there is no cross-resistance. Its spectrum is gram-positive: staphylococci, streptococci and some anaerobes. Systemic use is limited by severe nephrotoxicity, and it is also the classic disc test used to distinguish group A streptococci.

Targets: Undecaprenyl pyrophosphate (C55 lipid carrier), Peptidoglycan precursor transport, Protein disulfide isomerase (in vitro)

• · Standard over-the-counter strength is 500 units per gram, often combined with neomycin and polymyxin B. A thin film is enough. Do not use for more than about a week on intact skin — prolonged use selects resistant flora and drives contact sensitisation.
• · 500 units per gram in a sterile ophthalmic base, used for superficial bacterial conjunctivitis and blepharitis for 7-10 days.
• · The old paediatric label was 800-1000 units/kg/day for staphylococcal pneumonia in infants. The FDA requested withdrawal of injectable bacitracin in January 2020 because the nephrotoxicity risk was not justified by any remaining clinical need. This route is now essentially historical.

Work out your exact syringe units →

• very commonNephrotoxicity— With injectable use only — proteinuria, azotaemia and tubular necrosis. This is why the injection was withdrawn.
• very commonInjection-site pain— The intramuscular formulation was painful enough to require procaine in the diluent.
• commonAllergic contact dermatitis— Bacitracin is a top-ranked contact allergen in patch testing. Redness and itching that worsens rather than improves with continued application is usually allergy, not infection.
• rareAnaphylaxis from topical application— Genuinely documented, most often when applied to large open wounds or mucosa. It is the reason many surgical services no longer use topical bacitracin.

• Known bacitracin hypersensitivity, including prior contact dermatitis to it.
• Application to large surface areas, deep wounds, or punctures — absorption and anaphylaxis risk rise sharply.
• Any systemic or intramuscular use, which the FDA moved to withdraw in 2020.
• Not for use in the eye unless the product is a sterile ophthalmic preparation.

• synergyneomycin — Combined in triple-antibiotic ointment to add gram-negative coverage, though neomycin carries its own high rate of contact allergy.
• synergypolymyxin-b — The standard pairing in double- and triple-antibiotic ointments; bacitracin covers gram-positives, polymyxin B covers gram-negatives.
• cautionaminoglycosides — Additive nephrotoxicity and neuromuscular blockade, relevant only to the historical injectable form.

• · For topical use, none beyond watching the wound and noticing if the surrounding skin becomes more inflamed rather than less.
• · Injectable use historically required daily renal function and urinalysis; the route is no longer available.

Available over the counter as a topical ointment in the US and many other countries. Injectable bacitracin was withdrawn from the US market at FDA request in 2020.

• FDA 2020 request for withdrawal of bacitracin for injection (label)
• Smack et al., randomised comparison of bacitracin ointment versus white petrolatum for ambulatory wound care (trial)
• North American Contact Dermatitis Group patch-test series data on bacitracin sensitisation (review)

A cyclic peptide that binds the isoprenyl pyrophosphate lipid carrier and blocks its dephosphorylation, halting the recycling step that ferries peptidoglycan subunits across the membrane. Because the target is a lipid carrier rather than an enzyme active site, resistance is uncommon - but the same chemistry makes it too nephrotoxic to give systemically.

Bacitracin is one of the commonest causes of allergic contact dermatitis from an over-the-counter product, and the presentation is deceptive: a spreading, itchy, worsening rash around a wound reads as infection, so people apply more of it. Anaphylaxis to topical bacitracin is rare but documented. The other error is systemic use, which is nephrotoxic enough that it has no modern place.

• Undecaprenyl pyrophosphate (bactoprenol) lipid carrier — Requires divalent zinc

  Blocks lipid carrier recycling, halting cell wall synthesis

Topical and local; no systemic onset to speak of.

• ?Whether routine topical antibiotic prophylaxis on clean wounds offers any benefit over plain petrolatum is doubted by dermatology guidance.