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. |
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 | 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 after topical use, negligible excretion into breast milk. M/P ratio not available. Compatible with breastfeeding, but avoid application to breast area to prevent infant ingestion. |
| 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. |
■ 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 component","Epithelial herpes simplex keratitis (dendritic keratitis)","Vaccinia, varicella, and other viral infections of the cornea and conjunctiva","Mycobacterial infections of the eye","Fungal diseases of ocular structures"]
| 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"] |
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| 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. |