BACITRACIN
Clinical safety rating: safe
Animal studies have demonstrated safety
Bacitracin inhibits bacterial cell wall synthesis by binding to bactoprenol pyrophosphate (C55-isoprenyl pyrophosphate) and preventing its dephosphorylation, thereby blocking the incorporation of peptidoglycan precursors. It is primarily active against Gram-positive bacteria.
| Metabolism | Bacitracin is not metabolized systemically; it is excreted unchanged in the urine following parenteral administration. Topical application results in minimal systemic absorption. No significant hepatic metabolism. |
| Excretion | Renal: 90-100% (glomerular filtration and tubular secretion); biliary/fecal: minimal, <1% |
| Half-life | Terminal elimination half-life: 1.5-2 hours in normal renal function; prolonged to 3-6 hours in renal impairment; clinically relevant for dosing interval adjustment in renal failure. |
| Protein binding | Approximately 10-20%; primarily bound to albumin and alpha-1-acid glycoprotein. |
| Volume of Distribution | 0.3-0.6 L/kg; distributed mainly in extracellular fluid with poor penetration into CSF, eyes, and brain. |
| Bioavailability | Intramuscular: 100% (complete absorption); topical: negligible (<0.1%) systemic absorption; oral: not absorbed due to degradation in GI tract. |
| Onset of Action | Intramuscular: peak effect at 1-2 hours; topical: local effect within 24-48 hours; no systemic absorption via intact skin. |
| Duration of Action | Intramuscular: 6-8 hours (due to rapid renal clearance); topical: variable, requires reapplication every 6-12 hours for local infections. |
Intramuscular: 10,000-25,000 units/kg/day divided every 6-8 hours. Topical: apply thin layer to affected area 1-3 times daily.
| Dosage form | OINTMENT |
| Renal impairment | Creatinine clearance (CrCl) 20-50 mL/min: administer every 12 hours. CrCl <20 mL/min: administer every 24 hours or avoid due to nephrotoxicity risk. |
| Liver impairment | No specific adjustment recommended; not hepatically metabolized. |
| Pediatric use | Intramuscular: 10,000-25,000 units/kg/day divided every 6-8 hours. Topical: same as adults. |
| Geriatric use | Assess renal function; reduce dose or interval according to CrCl due to age-related decline in renal function. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
No significant systemic drug interactions due to minimal absorption For topical use only not for eyes or deep wounds.
| Breastfeeding | Not known if bacitracin is excreted in human breast milk. Given its poor systemic absorption, excretion is likely minimal. Risk to nursing infant is probably low, but caution advised. |
| Teratogenic Risk | Bacitracin is not absorbed systemically after topical administration and has minimal systemic absorption after intramuscular injection. There are no adequate controlled studies in pregnant women. Animal studies have not shown teratogenicity. Risk to fetus is low but cannot be ruled out. Use only if clearly needed. |
■ FDA Black Box Warning
Bacitracin injection (IM) has a boxed warning for nephrotoxicity and respiratory arrest due to its potential for severe renal toxicity, particularly in patients with pre-existing renal impairment or those receiving other nephrotoxic drugs. Fatal anaphylactic reactions have been reported with topical use in rare cases.
| Common Effects | Hypersensitivity reactions |
| Serious Effects |
["Hypersensitivity to bacitracin or any component of the formulation","Renal impairment (for IM use; avoid unless potential benefit outweighs risk)","Concurrent use with other nephrotoxic drugs (e.g., aminoglycosides, vancomycin) (for IM use)","Infants (IM use is contraindicated in neonates due to risk of renal toxicity and respiratory depression; however, it has been used in some settings with extreme caution)"]
| Precautions | ["Nephrotoxicity: IM use can cause acute tubular necrosis and renal failure; monitor renal function frequently.","Anaphylaxis: Severe hypersensitivity reactions including anaphylaxis have occurred with topical use, especially in patients with prior sensitivity.","Neuromuscular blockade: Bacitracin may potentiate neuromuscular blocking agents; use caution with anesthesia.","Superinfection: Prolonged use may result in overgrowth of nonsusceptible organisms including fungi.","Ophthalmic use: Avoid contamination of ophthalmic preparations; do not use for prolonged periods without medical supervision.","Pregnancy: Limited data; use only if clearly needed."] |
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| Fetal Monitoring |
| No specific monitoring required. For intramuscular use, monitor renal function due to potential nephrotoxicity. |
| Fertility Effects | No known effects on fertility. No human data available. |
| Food/Dietary | No clinically significant food interactions with topical bacitracin. Systemic administration (rare) has no known food interactions. |
| Clinical Pearls | Bacitracin is a polypeptide antibiotic effective against Gram-positive bacteria, primarily used topically for skin infections. It is not absorbed systemically when applied to intact skin, but can be nephrotoxic if used on large wounds or burns due to absorption. It is often combined with neomycin and polymyxin B (e.g., Neosporin). Intramuscular administration is limited to infants with staphylococcal pneumonia or empyema. Always monitor renal function if systemic absorption is possible. |
| Patient Advice | Apply a thin layer of bacitracin to the affected area 1 to 3 times daily. · Do not use on large areas of broken skin, deep wounds, or animal bites without consulting a doctor. · Avoid contact with eyes and mucous membranes. · Stop use and inform your doctor if irritation, rash, or swelling occurs. · Finish the full course of treatment as prescribed, even if symptoms improve. |