NEOMYCIN AND POLYMYXIN B SULFATES AND GRAMICIDIN
Clinical safety rating: safe
Other nephrotoxic or ototoxic drugs increase risk of toxicity Can cause ototoxicity and nephrotoxicity with systemic use.
Neomycin and gramicidin are aminoglycoside and polypeptide antibiotics, respectively, that inhibit bacterial protein synthesis by binding to the 30S and 50S ribosomal subunits, while polymyxin B is a cationic detergent that disrupts bacterial cell membrane integrity by binding to lipopolysaccharides.
| Metabolism | Neomycin: minimally metabolized, primarily renal excretion; Polymyxin B: not metabolized, primarily renal excretion; Gramicidin: not metabolized, primarily renal excretion. |
| Excretion | Neomycin and polymyxin B sulfates and gramicidin are poorly absorbed from intact skin or ophthalmic sites. After topical application, absorbed neomycin is excreted primarily unchanged in urine (30-50% of absorbed dose) via glomerular filtration; polymyxin B is excreted slowly via renal tubular secretion and glomerular filtration (60-70% of absorbed dose in urine); fecal elimination accounts for minor amounts. Gramicidin is not significantly absorbed. |
| Half-life | Neomycin: plasma half-life ~2-3 hours in patients with normal renal function, but can extend to 12-24 hours or more in renal impairment. Polymyxin B: half-life ~6 hours in normal renal function, prolonged significantly in renal failure (up to 2-3 days). Gramicidin: not systemically absorbed; half-life not applicable. |
| Protein binding | Neomycin: <10% bound to serum proteins. Polymyxin B: approximately 60% bound to serum proteins. Gramicidin: not systemically absorbed; binding not clinically relevant. |
| Volume of Distribution | Neomycin: Vd ~0.2-0.4 L/kg (limited distribution due to high polarity). Polymyxin B: Vd ~0.5-0.8 L/kg (distributes mainly in extracellular fluid). Gramicidin: not applicable. |
| Bioavailability | Topical and ophthalmic: Bioavailability is negligible (<0.1%) due to poor absorption through intact skin and mucosa. Oral: Not used systemically (highly toxic if absorbed). Intravenous: Not available. |
| Onset of Action | Ophthalmic use: Onset of antibacterial effect occurs within 1-2 hours after application. Topical dermatologic: Onset varies depending on infection severity; clinical improvement typically seen within 24-48 hours. |
| Duration of Action | Ophthalmic: Duration of activity is approximately 6-8 hours after a single dose, requiring frequent administration (every 4-6 hours). Topical: Duration depends on formulation and site; typically 12 hours after application. |
1-2 drops or a small amount applied to affected eye(s) every 4 hours, or more frequently if severe, for up to 7-10 days. Ophthalmic ointment: apply a 1/2-inch ribbon into conjunctival sac every 3-4 hours.
| Dosage form | SOLUTION/DROPS |
| Renal impairment | No dose adjustment required for topical ophthalmic use due to negligible systemic absorption. |
| Liver impairment | No dose adjustment required for topical ophthalmic use. |
| Pediatric use | Safety and efficacy in children <2 years have not been established. For children >=2 years, same as adult dosing. |
| Geriatric use | No specific dose adjustments; use with caution due to potential for prolonged healing or increased sensitivity. |
| 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 | Minimal systemic absorption suggests negligible excretion into breast milk; no M/P ratio available. Use caution on large areas or broken skin due to potential for infant ingestion of topically applied drug. Consider benefit-risk; generally compatible with breastfeeding. |
| Teratogenic Risk | Neomycin and polymyxin B (both poorly absorbed) and gramicidin (not absorbed) present negligible systemic exposure following topical or otic administration; no known teratogenic effects in humans. However, neomycin has been associated with ototoxicity and nephrotoxicity when absorbed systemically. Avoid use on broken skin or in large areas during pregnancy, especially first trimester. FDA Pregnancy Category C for neomycin (systemic) and D for polymyxin B (systemic); topical use considered low risk. |
■ FDA Black Box Warning
None
| Common Effects | topical infections |
| Serious Effects |
["Hypersensitivity to any component of the product.","Known or suspected viral infections of the eye (e.g., herpes simplex, vaccinia, varicella).","Fungal infections of the eye."]
| Precautions | ["Prolonged use may result in overgrowth of nonsusceptible organisms including fungi.","Hypersensitivity reactions, including contact dermatitis, may occur.","Ototoxicity and nephrotoxicity risk with systemic absorption if applied to open wounds or damaged skin.","Use with caution in patients with renal impairment or hearing loss."] |
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| Fetal Monitoring | No specific monitoring required for topical/otic use. If used on extensive wounds or mucosal surfaces, monitor for signs of nephrotoxicity (urine output, serum creatinine) and ototoxicity (hearing loss, tinnitus). For prolonged use, consider audiometry and renal function tests. |
| Fertility Effects | No known effects on fertility from topical/otic use. Systemic neomycin may impair spermatogenesis in animal studies at high doses, but relevance to humans is unknown. |