Bacitracin
Bacitracin
Generic Name
Bacitracin
Mechanism
* Interference with peptidoglycan biosynthesis – Bacitracin binds to the dephosphorylated form of the bactoprenyl carrier (C55‑pyrophosphate), preventing its re‑phosphorylation.
* Inhibition of lipid carrier recycling – By sequestering the carrier, it blocks MurA–MurF enzymes and disrupts translocation of cell‑wall precursors across the plasma membrane.
* Result – Rapid inhibition of cell wall synthesis in Gram‑positive organisms with high cell wall turnover (e.g., *Staphylococcus aureus*, *Enterococcus faecalis*).
Pharmacokinetics
| Parameter | Value/Comment |
| Absorption | Poor systemic absorption when used topically. |
| Distribution | Low plasma levels; negligible tissue penetration. |
| Metabolism | Not metabolized; excreted unchanged. |
| Excretion | Primarily renal, mainly via the kidneys (≈90% unchanged). |
| Half‑life | ~1.5–2 h in healthy adults. |
| Bioavailability | Negligible ( *Because of minimal systemic exposure, bacitracin is rarely associated with systemic toxicity when used topically.*
Indications
* Topical treatment of superficial cutaneous, perineal, and mucocutaneous infections caused by susceptible Gram‑positive bacteria.
* Preservation agent in ophthalmic solutions (e.g., ophthalmic antibiotic eye drops) to prevent bacterial growth.
* Additive in over‑the‑counter ointments (e.g., bacitracin–polymyxin B) for minor wounds and burns.
Contraindications
* Allergy to bacitracin or other polypeptide antibiotics.
* Renal impairment – although topical use is safe, systemic side effects (e.g., acute interstitial nephritis) can occur with accidental ingestion or large surface application.
* Ototoxicity – avoid aqueous solutions in patients with hearing loss or concurrent ototoxic drugs.
* Pregnancy – considered category C; limited data, but topical use is generally acceptable if benefits outweigh risks.
* Lactation – minimal systemic absorption; usually considered safe.
Dosing
| Form | Dose / Frequency | Notes |
| Bacitracin ointment (7.5 WPU) | Apply 1 g (roughly a finger‑breadth thickness) to affected area 2–4 × daily. | Used on intact skin, non‑infected wounds. |
| Bacitracin ophthalmic solution (0.5 %) | 1–2 drops into each eye 4–6 × daily (or per provider’s instruction). | Use only as directed; not for glaucoma patients unless otherwise prescribed. |
| Bacitracin/Polymyxin B ointment (both 7.5 WPU) | Same dosing as bacitracin alone; provides broad‑spectrum coverage. | For superficial skin or external ear infections. |
> *Avoid prolonged (>10 days) ocular or extensive skin use to reduce risk of nephro‑/ototoxicity.*
Adverse Effects
Common (≤10 %)
* Local irritation, itching, or rash at application site.
* Mild burning or stinging of eyes (ophthalmic use).
Serious (>1 %)
* Acute interstitial nephritis – may present with hematuria, proteinuria, or decreased renal function (especially after inadvertent ingestion).
* Angioedema or severe hypersensitivity reactions.
* Ototoxicity – hearing loss, tinnitus with systemic exposure or high‑dose ocular usage.
Monitoring
| Parameter | Frequency | Rationale |
| Renal function (serum creatinine, BUN) | Prior to prolonged use if risk factors present; repeat if clinical signs of nephrotoxicity develop. | Detect early interstitial nephritis. |
| Ocular status | During prolonged ophthalmic therapy (>7 days). | Detect changes in vision or hearing. |
| Allergic reactions | Monitor after first application, especially in patients with drug allergies. | Early identification of hypersensitivity. |
Clinical Pearls
1. Limited systemic absorption – Bacitracin’s safety margin is largely due to minimal bioavailability; still, caution in large‑area application or in patients with severe renal disease.
2. “Ophthalmic bacitracin is a preservative” – In many ophthalmic solutions, bacitracin serves as a preservative rather than the active antimicrobial; this reduces systemic exposure.
3. Polymyxin B synergy – When combined with polymyxin B, bacitracin provides coverage against both Gram‑positive and Gram‑negative organisms in topical formulations, useful for burn wounds.
4. Contraindicated in patients on aminoglycosides – Ototoxicity risk is additive; avoid concurrent use of bacitracin eye drops in patients receiving other ototoxic agents.
5. Use caution in diabetic foot ulcers – Excessive topical bacitracin may delay epithelialization; consider alternative agents when systemic infection is suspected.
> *Stay informed about local antibiograms; bacitracin resistance is uncommon on topical use, but empirical therapy should still consider susceptibility patterns.*
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• *Sources: UpToDate, Goodman & Gilman’s The Pharmacological Basis of Therapeutics, FDA prescribing information.*