NEOMYCIN AND POLYMYXIN B SULFATES AND BACITRACIN ZINC
Clinical safety rating: safe
Other nephrotoxic or ototoxic drugs increase risk of toxicity Can cause ototoxicity and nephrotoxicity with systemic use.
Neomycin is an aminoglycoside that binds to the 30S ribosomal subunit, causing misreading of mRNA and inhibition of protein synthesis. Polymyxin B is a polypeptide that disrupts bacterial cell membrane permeability by interacting with phospholipids. Bacitracin inhibits bacterial cell wall synthesis by interfering with dephosphorylation of the lipid carrier in peptidoglycan biosynthesis.
| Metabolism | Neomycin: Not significantly metabolized; excreted unchanged in urine after systemic absorption. Polymyxin B: Not well characterized; likely hepatic metabolism. Bacitracin: Not metabolized; excreted primarily unchanged in urine. |
| Excretion | Renal: ~90% of absorbed neomycin and polymyxin B; bacitracin zinc: minimal systemic absorption, excreted primarily in feces. For neomycin: ~99% fecal after oral; polymyxin B: ~60% renal, rest biliary; bacitracin: nearly 100% renal if absorbed. |
| Half-life | Neomycin: 2-3 h (terminal), prolonged in renal impairment; polymyxin B: 6-7 h (terminal), extended in renal failure; bacitracin: 1.5 h (if absorbed), not clinically relevant due to minimal absorption. |
| Protein binding | Neomycin: 0-30% (low); polymyxin B: ~50-60% (albumin); bacitracin: minimal (<10%). |
| Volume of Distribution | Neomycin: 0.2-0.4 L/kg (limited to extracellular fluid); polymyxin B: 0.5-0.7 L/kg; bacitracin: not meaningful due to poor absorption. |
| Bioavailability | Oral: <3% for aminoglycosides (neomycin), negligible for polymyxin B and bacitracin; topical: minimal systemic absorption except through broken skin; ophthalmic: negligible systemic. |
| Onset of Action | Topical: within 24-48 h for bacterial suppression; ophthalmic: within hours; irrigations: immediate local effect. Oral: not absorbed, acts locally in gut. |
| Duration of Action | Topical: effects last while drug present; ophthalmic: every 4-6 h dosing needed. Systemic effect only if large wounds or renal impairment causing accumulation. |
Apply thin layer to affected area 2-3 times daily. For ophthalmic use: 1-2 drops in affected eye every 4 hours, or 1/2 inch ribbon of ointment in conjunctival sac 2-3 times daily.
| Dosage form | OINTMENT |
| Renal impairment | Not applicable for topical use due to minimal systemic absorption. For oral neomycin component (not typical combination): GFR 30-50 mL/min: reduce dose by 50%; GFR <30 mL/min: avoid or extend interval. |
| Liver impairment | No adjustment required for topical use. |
| Pediatric use | Same as adult dosing for topical application. For ophthalmic use in children: 1-2 drops in affected eye every 4 hours, or ointment 1/2 inch ribbon 2-3 times daily. |
| Geriatric use | No specific dosage adjustment needed; use with caution in elderly due to potential skin thinning or increased systemic absorption through compromised skin. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Other nephrotoxic or ototoxic drugs increase risk of toxicity Can cause ototoxicity and nephrotoxicity with systemic use.
| FDA category | Animal |
| Breastfeeding | Systemic absorption of bacitracin and polymyxin B is negligible; neomycin is poorly absorbed. M/P ratio not applicable due to minimal systemic presence. Compatible with breastfeeding; avoid application to breast area to prevent infant ingestion. |
| Teratogenic Risk | Neomycin: No evidence of fetal harm in animal studies; Polymyxin B: No malformations in animal studies; Bacitracin: Not absorbed significantly, minimal risk. First trimester: Theoretical risk from systemic absorption is low. Second/third trimesters: No reported adverse fetal effects from topical use. |
■ FDA Black Box Warning
Neomycin is nephrotoxic and ototoxic, even following topical application, especially in patients with renal impairment or prolonged use; avoid use in extensive areas or open wounds. Bacitracin may cause nephrotoxicity if systemically absorbed.
| Common Effects | topical infections |
| Serious Effects |
Hypersensitivity to any component; substantial burns or extensive denuded areas due to increased absorption; renal impairment.
| Precautions | Risk of ototoxicity and nephrotoxicity with neomycin; avoid prolonged use on extensive areas. Sensitization and allergic reactions may occur. Overgrowth of nonsusceptible organisms, including fungi. Not for ophthalmic or internal use. |
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| Fetal Monitoring | No specific monitoring required for topical use. Monitor for signs of systemic toxicity (e.g., nephrotoxicity, ototoxicity) only if applied to large areas of damaged skin. |
| Fertility Effects | No known effects on fertility in humans. Animal studies with neomycin showed no impairment of fertility. |