NEOMYCIN AND POLYMYXIN B SULFATES AND DEXAMETHASONE
Clinical safety rating: safe
Other nephrotoxic or ototoxic drugs increase risk of toxicity Can cause ototoxicity and nephrotoxicity with systemic use.
Neomycin and polymyxin B sulfates are aminoglycoside and polypeptide antibiotics, respectively, that inhibit bacterial protein synthesis and disrupt bacterial cell membrane integrity. Dexamethasone is a corticosteroid that suppresses inflammation by inhibiting phospholipase A2, reducing prostaglandin and leukotriene synthesis.
| Metabolism | Neomycin and polymyxin B are minimally absorbed after ophthalmic administration; if absorbed, neomycin is excreted unchanged by kidneys, polymyxin B undergoes minimal metabolism. Dexamethasone is metabolized in the liver by CYP3A4. |
| Excretion | Neomycin: ~99% of oral dose eliminated unchanged in feces; <1% absorbed renally excreted. Polymyxin B: ~60% renal elimination of absorbed fraction; remainder non-renal via biliary/fecal. Dexamethasone: ~65% renal as metabolites, <10% unchanged; ~35% fecal. |
| Half-life | Neomycin: 2-3 hours (IM/IV, if absorbed); Polymyxin B: 6-7 hours; Dexamethasone: 3-4.5 hours. Clinically, neomycin's half-life is not relevant due to minimal absorption; polymyxin B prolonged in renal impairment; dexamethasone CNS effect lasts > half-life. |
| Protein binding | Neomycin: <10% (albumin); Polymyxin B: ~80% (albumin, α1-acid glycoprotein); Dexamethasone: ~77% (albumin, corticosteroid-binding globulin). |
| Volume of Distribution | Neomycin: ~0.2 L/kg (extracellular fluid); Polymyxin B: ~0.5 L/kg (interstitial); Dexamethasone: ~0.6 L/kg (total body water). |
| Bioavailability | Oral neomycin: <3%; polymyxin B: negligible; dexamethasone: 80-90% oral. Ophthalmic/otic: minimal systemic absorption (<1% for all). |
| Onset of Action | Otic/ophthalmic: Neomycin/polymyxin B bacterial inhibition within 1-2 hours; dexamethasone anti-inflammatory within 1-3 hours. Topical: similar. |
| Duration of Action | Otic/ophthalmic: Neomycin/polymyxin B effect lasts 6-12 hours; dexamethasone 12-24 hours. Topical: antimicrobial duration 6-12 hours; anti-inflammatory 12-36 hours. |
| Molecular Weight | 1280.58 |
Ophthalmic: 1-2 drops in affected eye(s) every 3-4 hours; severe infections: 1-2 drops every 1-2 hours, then taper. Otic: 3-4 drops in affected ear(s) 3-4 times daily.
| Dosage form | SUSPENSION/DROPS |
| Renal impairment | No adjustment required for ophthalmic or otic use due to minimal systemic absorption. |
| Liver impairment | No adjustment required for ophthalmic or otic use due to minimal systemic absorption. |
| Pediatric use | Ophthalmic: 1-2 drops in affected eye(s) every 3-4 hours; severe infections: 1-2 drops every 1-2 hours, then taper. Otic: 3-4 drops in affected ear(s) 3-4 times daily. Use with caution in infants. |
| Geriatric use | Same as adult dosing. Monitor intraocular pressure with prolonged ophthalmic use due to dexamethasone. |
| 1st trimester | Generally avoided due to teratogenic potential; systemic absorption minimal but caution advised. Corticosteroids have been associated with low birth weight and cleft palate. Only use if benefit outweighs risk. |
| 2nd trimester | Use with caution; limited human data. Dexamethasone has known fetal effects. Consider risk-benefit. |
| 3rd trimester | Use with caution; prolonged use or high doses may cause hypothalamic-pituitary-adrenal suppression in neonate. Avoid near term if possible. |
Clinical note
Other nephrotoxic or ototoxic drugs increase risk of toxicity Can cause ototoxicity and nephrotoxicity with systemic use.
| FDA category | Animal |
| Placental transfer | Dexamethasone readily crosses the placenta; neomycin and polymyxin B have limited transfer due to molecular size and polarity. |
■ FDA Black Box Warning
Not assigned. However, neomycin is associated with nephrotoxicity and ototoxicity with systemic absorption, but this is not a boxed warning for ophthalmic use.
| Common Effects | topical infections |
| Serious Effects |
Hypersensitivity to any componentOcular tuberculosisFungal infections of the eyeViral infections (e.g., herpes simplex, vaccinia, varicella)Perforated tympanic membrane (otic use)
| Precautions | Prolonged use may lead to fungal superinfection or secondary ocular infections, Risk of increased intraocular pressure with prolonged corticosteroid use, Neomycin may cause skin sensitization; discontinue if irritation occurs, Use with caution in patients with glaucoma, corneal thinning, or herpes simplex keratitis |
| Food/Dietary | No known food interactions. No dietary restrictions required. |
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| Breastfeeding |
| Minimal systemic absorption due to topical/ophthalmic use. Dexamethasone is excreted in low amounts; unlikely to cause adverse effects in infant. Use smallest effective dose for shortest duration. |
| Lactation Rating | L2 (probably compatible) |
| Teratogenic Risk | First trimester: Limited data; neomycin and polymyxin B are poorly absorbed, systemic levels negligible. Dexamethasone is a corticosteroid; association with oral clefts at very high doses, but topical use with low systemic absorption considered low risk. Second/third trimesters: No known fetal toxicity from topical use. Avoid prolonged use in high doses due to theoretical risk of adrenal suppression. |
| Fetal Monitoring | Monitor for maternal skin irritation or hypersensitivity. No specific fetal monitoring required for topical use. For prolonged use, monitor for maternal adrenal suppression (rare). |
| Fertility Effects | No known adverse effects on fertility from topical use at recommended doses. |
| Clinical Pearls | This is a combination otic suspension for bacterial otitis externa and superficial bacterial keratitis. Neomycin is an aminoglycoside, polymyxin B is a polymyxin, and dexamethasone is a corticosteroid. Neomycin carries risk of ototoxicity if applied to a perforated tympanic membrane; contraindicated in tympanic membrane perforation. Polymyxin B covers gram-negative rods including Pseudomonas. Corticosteroid component reduces inflammation but may mask infection, prolong fungal infections, or increase intraocular pressure in ophthalmic use. Shake well before use. For otic use, warm bottle in hands to avoid vertigo. Instill 4 drops into affected ear(s) 3-4 times daily for up to 10 days. For ophthalmic use, instill 1-2 drops into conjunctival sac 4-6 times daily; maximum duration 10 days to avoid steroid-induced glaucoma/cataracts. Do not use in viral or fungal infections. |
| Patient Advice | Shake the bottle well before each use. · For ear infections: lie on your side for 5 minutes after instilling drops to allow medication to reach the ear canal. · Do not touch the dropper tip to any surface, including the ear or eye, to avoid contamination. · Complete the full course of treatment even if symptoms improve. · Report any hearing loss, ringing in the ears, dizziness, or worsening of symptoms to your healthcare provider immediately. · Avoid swimming or getting water in the ear during treatment. · For eye infections: remove contact lenses before use and wait 15 minutes before reinserting. · Do not use this medication for longer than prescribed (typically 7-10 days) due to risk of side effects. · If you have a perforated eardrum, do not use this medication in the ear. |