Dexamytrex (Dexamethasone/Gentamicin Ophthalmic Preparation)
Dexamytrex is a combination ophthalmic ointment containing neomycin, polymyxin B sulfates, and dexamethasone, indicated for steroid-responsive inflammatory ocular conditions where bacterial infection or risk of infection exists, applied 3-4 times daily to the conjunctival sac. 1
Indications
This combination product is used for:
- Steroid-responsive inflammatory conditions of the eye where bacterial infection is present or there is risk of bacterial infection
- External ocular infections requiring both anti-inflammatory and anti-infective treatment
- Conditions where the dual benefit of corticosteroid (to reduce inflammation) and antibiotic coverage (gentamicin/polymyxin B/neomycin) is needed
The rationale is that external ophthalmic infections often require both antibiotics to reach therapeutic levels above the minimal inhibitory concentration (MIC) and corticosteroids to limit precorneal damage caused by infection 2.
Dosing
Apply a small amount (approximately 1/2 inch) into the conjunctival sac(s) 3-4 times daily 1.
Application technique:
- Tilt head back
- Pull down lower lid to form a "V" pocket between eyeball and lower lid
- Place approximately 1/2 inch of ointment in the pocket
- Avoid touching the tube tip to the eye
- Look downward before closing the eye 1
Important prescribing limitations:
- No more than 8 grams should be prescribed initially
- Do not refill without further evaluation - this is critical to monitor for complications such as increased intraocular pressure, which can lead to glaucoma with prolonged corticosteroid use 1, 2
Absolute Contraindications
This medication is absolutely contraindicated in the following conditions 1:
- Epithelial herpes simplex keratitis (dendritic keratitis) - corticosteroids can worsen viral infections
- Vaccinia
- Varicella
- Other viral diseases of the cornea and conjunctiva
- Mycobacterial infection of the eye
- Fungal diseases of ocular structures
- Known or suspected hypersensitivity to any component (particularly the antibiotic component, which has higher rates of hypersensitivity)
Critical Clinical Pitfalls
Viral keratitis misdiagnosis
The most dangerous pitfall is using this medication in viral keratitis, particularly herpes simplex. The 2024 Bacterial Keratitis Preferred Practice Pattern emphasizes proper diagnosis before initiating treatment 3. Always rule out dendritic keratitis before prescribing any steroid-containing preparation.
Prolonged use risks
Repeated administration of corticosteroids can increase intraocular pressure and lead to glaucoma 2. This is why the FDA label specifically limits initial prescriptions to 8 grams and prohibits refills without re-evaluation 1.
Antibiotic component considerations
The neomycin component has a higher rate of hypersensitivity reactions compared to other components 1. Monitor for allergic reactions, particularly with repeated use.
Relationship to Current Guidelines
The 2024 Bacterial Keratitis guidelines discuss fortified antibiotic preparations for severe infections, noting that gentamicin can be fortified to 14 mg/ml for topical use 3. However, for routine external infections with inflammatory components, the commercial combination product provides adequate coverage with the added benefit of dexamethasone for inflammation control.
The combination approach is supported by research showing that concomitant release of both drugs during the first 10 hours of treatment, followed by adequate gentamicin concentrations above the MIC for 50 hours, provides optimal therapeutic benefit 2.