NEOMYCIN AND POLYMYXIN B SULFATE
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 antibiotic that binds to the 30S ribosomal subunit, causing misreading of mRNA and inhibiting protein synthesis. Polymyxin B sulfate is a cationic detergent that disrupts bacterial cell membrane permeability by interacting with phospholipids, leading to cell death.
| Metabolism | Neomycin is minimally absorbed after topical application; absorbed fraction is primarily excreted unchanged by the kidneys. Polymyxin B is also minimally absorbed; systemic metabolism is negligible. |
| Excretion | Renal: ~90-95% (neomycin, polymyxin B) unchanged; fecal: 5-10% (biliary excretion negligible). |
| Half-life | Neomycin: 2-3 hours (normal renal function), prolonged to 24-48 hours in renal impairment; Polymyxin B: 4.5-6 hours (normal renal function), extended significantly in renal failure. |
| Protein binding | Neomycin: negligible (<10%); Polymyxin B: moderate (50-60%), primarily to albumin. |
| Volume of Distribution | Neomycin: 0.2-0.3 L/kg (mainly extracellular); Polymyxin B: 0.6-0.8 L/kg (distributes to extravascular tissues, low CNS penetration). |
| Bioavailability | Oral: <3% (local effect only, minimal systemic absorption); Topical/ophthalmic/irrigation: negligible (<1% systemic). |
| Onset of Action | Oral: 1-2 hours (local GI effect); Topical: minutes (local antibacterial); Ophthalmic: 15-30 minutes; Irrigation: immediate. |
| Duration of Action | Oral: 6-12 hours (local); Topical/ophthalmic: 6-8 hours; Irrigation: varies with irrigation rate; renal elimination limits duration systemically. |
| Molecular Weight | Neomycin: 614.65 Da (neomycin B); Polymyxin B: 1301.56 Da (polymyxin B1, B2 mixture; average ~1285 Da) |
For irrigation of urinary bladder: 1 mL of solution containing 40 mg neomycin and 200,000 units polymyxin B per mL diluted in 1 liter of 0.9% sodium chloride, instilled via continuous irrigation at a rate of 1 liter per 24 hours. For topical use: apply thin layer to affected area 2-4 times daily.
| Dosage form | SOLUTION |
| Renal impairment | Neomycin is significantly excreted renally; accumulation may occur in renal impairment. Avoid systemic use in renal failure (CrCl <30 mL/min). For topical or irrigation use, risk of systemic absorption is low but caution is advised in severe renal impairment. |
| Liver impairment | No dosage adjustment required for hepatic impairment. Neomycin is not metabolized by the liver and is excreted renally. |
| Pediatric use | Neomycin and polymyxin B sulfate for bladder irrigation: not established in pediatric patients. For topical use: apply thin layer to affected area 2-4 times daily. Safety and efficacy not established for systemic use in children. |
| Geriatric use | Use with caution due to age-related renal impairment. Monitor renal function and consider dose reduction if using prolonged irrigation. For topical use, no specific adjustment needed but avoid application to large areas or broken skin. |
| 1st trimester | Neomycin and polymyxin B sulfate are poorly absorbed after topical application; however, if significant systemic absorption occurs (e.g., on large wounds or damaged skin), potential for fetal risk exists due to nephrotoxicity and ototoxicity. Avoid use in first trimester unless benefit outweighs risk. |
| 2nd trimester | Similar to first trimester; systemic absorption is minimal with intact skin but caution with extensive areas or compromised skin. Use only if clearly needed. |
| 3rd trimester | Avoid use near term due to theoretical risk of neonatal nephrotoxicity and ototoxicity if absorbed. Caution with prolonged or extensive use. |
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 and polymyxin B are poorly absorbed; significant placental transfer is unlikely with proper topical use. Data limited but minimal systemic absorption suggests negligible transfer. |
■ FDA Black Box Warning
Neomycin is potentially nephrotoxic and ototoxic (vestibular and cochlear). The risk is increased in patients with renal impairment, pre-existing hearing loss, or prolonged use. Polymyxin B can cause nephrotoxicity and neurotoxicity. Combined use of neomycin and polymyxin B may increase these risks.
| Common Effects | topical infections |
| Serious Effects |
Hypersensitivity to neomycin, polymyxin B, or any component of the formulationKnown allergy to aminoglycosides (neomycin) or polymyxinsApplication to large open wounds or extensive skin areas with impaired renal function (risk of systemic toxicity)
| Precautions | Prolonged use may result in overgrowth of nonsusceptible organisms including fungi., Cross-allergenicity among aminoglycosides may occur., Ophthalmic use only; not for injection or irrigation., Discontinue if sensitivity or irritation occurs., Caution in patients with renal impairment or myasthenia gravis due to potential neuromuscular blockade. |
Loading safety data…
| Breastfeeding | Neomycin and polymyxin B are not absorbed systemically after topical application; therefore, minimal excretion into breast milk is expected. Considered compatible with breastfeeding when applied to small areas. Avoid application to breast or large areas where infant may ingest directly. |
| Lactation Rating | L2 (Probably Compatible) |
| Teratogenic Risk | FDA Pregnancy Category D for neomycin; polymyxin B is Category C. Both cross placenta. First trimester: potential ototoxicity and nephrotoxicity minimal due to poor absorption; systemic exposure from topical use negligible. Second and third trimesters: theoretical risk of fetal ototoxicity and nephrotoxicity if significant maternal systemic absorption occurs. Data insufficient to quantify risk. |
| Fetal Monitoring | Monitor maternal renal function (serum creatinine, BUN) and hearing if prolonged treatment or underlying renal impairment. For fetal monitoring, standard antenatal surveillance. Assess for signs of ototoxicity or nephrotoxicity in neonate if maternal toxicity suspected. |
| Fertility Effects | No known direct effects on fertility. Animal studies with neomycin showed no impairment. Systemic absorption minimal; unlikely to affect reproductive organs or gametes. |
| Food/Dietary | No significant food interactions. This is a topical medication with negligible systemic absorption; no dietary restrictions required. |
| Clinical Pearls | Neomycin and polymyxin B sulfate combination is typically used topically for superficial skin infections. Neomycin is an aminoglycoside antibiotic with potential for ototoxicity and nephrotoxicity if absorbed through broken skin or mucosal surfaces; avoid use on large wounds or burns. Polymyxin B is a polypeptide antibiotic effective against Gram-negative bacteria, including Pseudomonas. This combination is often found in otic suspensions for otitis externa; ensure tympanic membrane is intact to prevent ototoxicity. Monitor for allergic contact dermatitis with prolonged use. |
| Patient Advice | Apply a thin layer to the affected skin; do not cover with occlusive dressings unless directed. · Avoid use on large areas of broken skin, deep wounds, or severe burns to minimize absorption. · Do not use in the ear if the eardrum is perforated; seek medical advice if you have ear drainage or hearing loss. · Notify your doctor if you develop rash, itching, or worsening of skin condition; this may indicate an allergy. · Use for the full prescribed duration; do not use longer than 1 week unless advised by your doctor. |