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. |
| Molecular Weight | Neomycin: 908.9 Da (neomycin B); Polymyxin B: 1301.6 Da (average); Bacitracin: 1422.7 Da. Combined product: variable, but all >500 Da. |
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 | Avoid use in first trimester unless clearly needed; risk of ototoxicity and nephrotoxicity to fetus. Considered FDA Pregnancy Category D. |
| 2nd trimester | Use only if potential benefit justifies risk to fetus; caution due to potential for fetal harm from aminoglycosides and polymyxins. |
| 3rd trimester | Avoid prolonged or high-dose use; theoretical risk of fetal ototoxicity and nephrotoxicity, especially with neomycin. |
Clinical note
Other nephrotoxic or ototoxic drugs increase risk of toxicity Can cause ototoxicity and nephrotoxicity with systemic use.
| FDA category | Animal |
| Placental transfer | Neomycin: limited data, but aminoglycosides cross placenta; polymyxin B: minimal placental transfer; bacitracin: placental transfer not well studied, but likely low due to high molecular weight. |
■ 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 (neomycin, polymyxin B, bacitracin)Myasthenia gravis (risk of neuromuscular blockade from neomycin and polymyxin B)Severe renal impairment (accumulation of neomycin and polymyxin B)Pre-existing hearing loss (ototoxicity risk with neomycin)
| 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. |
| Food/Dietary |
Loading safety data…
| Breastfeeding |
| Neomycin and polymyxin B are poorly absorbed orally; bacitracin is not significantly absorbed. Minimal systemic absorption suggests low risk to nursing infant, but caution due to potential alteration of infant gut flora. Monitor for diarrhea or allergic reactions. |
| Lactation Rating | L2 (Safer) - limited data but likely compatible with breastfeeding due to poor oral absorption. |
| 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. |
| 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. |
| None known for topical administration. Avoid oral ingestion. |
| Clinical Pearls | This triple antibiotic ointment is indicated for topical use only; avoid application to large areas of denuded skin due to risk of systemic absorption, particularly neomycin which can cause ototoxicity. Neomycin is a common contact allergen; consider patch testing in patients with prolonged use or rash. Bacitracin zinc has a low but present risk of anaphylaxis. Polymyxin B is active against gram-negative bacilli including Pseudomonas. Do not use in eyes or ears with perforated tympanic membrane. |
| Patient Advice | Apply a thin layer to the affected area 1 to 3 times daily. · Wash hands before and after application unless treating hands. · Do not use on large wounds, deep cuts, or serious burns without medical advice. · Discontinue and contact your doctor if skin irritation, rash, or swelling occurs. · Antibiotics can cause allergic reactions; seek emergency help if you have trouble breathing or swelling of the face. · Do not use this product for longer than 1 week unless directed by a doctor. · Keep out of eyes, nose, mouth, and ears (if eardrum is torn). |