Usage
Dexamethasone + Gentamicin is prescribed for inflammatory eye conditions with or at risk of bacterial infection. This includes conditions like conjunctivitis, keratitis, blepharitis, hordeolum, chronic anterior uveitis, corneal injuries (chemical, radiation, thermal burns, foreign body), and post-operative eye infection prevention. It is also used for ear infections, particularly otitis externa with eczema.
Its pharmacological classifications are:
- Corticosteroid (Dexamethasone)
- Aminoglycoside Antibiotic (Gentamicin)
Mechanism of Action: Dexamethasone reduces inflammation by inhibiting inflammatory mediators like prostaglandins. Gentamicin inhibits bacterial protein synthesis, leading to bacterial cell death.
Alternate Names
Dexa-Gentamicin, DEEXA-G
Brand names vary depending on the region and manufacturer.
How It Works
Pharmacodynamics: Dexamethasone exerts anti-inflammatory and immunosuppressive effects. Gentamicin disrupts bacterial ribosome function, leading to bactericidal action.
Pharmacokinetics:
- Absorption: Topical application results in local action with limited systemic absorption. However, some systemic absorption can occur, especially with prolonged use or compromised corneal/skin integrity.
- Metabolism: Dexamethasone is metabolized primarily in the liver. Gentamicin is not metabolized.
- Elimination: Dexamethasone is excreted mainly in the urine. Gentamicin is primarily excreted unchanged in the urine via glomerular filtration.
Mode of Action: Dexamethasone binds to glucocorticoid receptors, altering gene transcription to suppress inflammation. Gentamicin irreversibly binds to the 30S ribosomal subunit of susceptible bacteria, interrupting protein synthesis.
Dosage
Standard Dosage
Adults:
- Ophthalmic: 1-2 drops every 4 hours for mild to moderate infections. For severe infections, 1-2 drops hourly, tapering as the condition improves. Ointment can be applied every 8-12 hours.
- Otic: 3-4 drops in the affected ear 3 times daily.
Children:
- Ophthalmic/Otic: Similar to adult dosing, but always consult pediatric guidelines and consider age and weight. For children under two years old safety and efficacy have not been established. For children below six years old otic administration requires doctor supervision.
Special Cases:
- Elderly Patients: Close monitoring for adverse effects, especially with prolonged use.
- Patients with Renal Impairment: Gentamicin dosage adjustment needed based on creatinine clearance.
- Patients with Hepatic Dysfunction: Caution advised with dexamethasone.
- Patients with Comorbid Conditions: Caution with diabetes, glaucoma, heart disease, and other conditions.
Clinical Use Cases
Dosage for specific settings follows standard recommendations, adjusted based on severity and patient factors.
Dosage Adjustments
Renal impairment requires gentamicin dose reduction.
Side Effects
Common Side Effects:
Eye: Minor irritation, burning, stinging, itching, redness, blurred vision.
Rare but Serious Side Effects:
Allergic reactions, corneal ulceration, glaucoma, cataracts.
Long-Term Effects:
Cushing’s syndrome, adrenal suppression (with systemic absorption).
Adverse Drug Reactions (ADR)
Severe allergic reactions, vision changes, increased intraocular pressure.
Contraindications
Hypersensitivity to dexamethasone or gentamicin, viral/fungal/mycobacterial eye infections, perforated tympanic membrane, herpes simplex keratitis. Relative contraindications include glaucoma, cataracts.
Drug Interactions
Antiviral eye drops (e.g., ganciclovir), other ophthalmic corticosteroids or antibiotics, ritonavir, cobicistat, amphotericin B, heparin, sulfadiazine, cephalotin, and cloxacillin.
Pregnancy and Breastfeeding
Use only if clearly needed, with careful risk-benefit assessment. Dexamethasone crosses the placenta and is present in breast milk. Gentamicin use during pregnancy should be restricted to life-threatening infections.
Drug Profile Summary
(As above)
Popular Combinations
Not applicable for a topical combination product.
Precautions
(As detailed in the side effects and contraindications sections above)
FAQs (Frequently Asked Questions)
Q1: What is the recommended dosage for Dexamethasone + Gentamicin?
A: Refer to the detailed dosage guidelines above.
Q2: What are the common side effects?
A: Eye irritation, burning, stinging, itching, and redness.
Q3: Can this medication be used during pregnancy?
A: Use with extreme caution and only if benefits outweigh the risks, after consulting with a specialist.
Q4: Are there any drug interactions I should be aware of?
A: Yes, see the drug interactions section for details.
Q5: How should I administer the eye drops?
A: Tilt head back, pull down the lower eyelid, instill drops into the conjunctival sac, avoid touching the tip of the bottle to the eye or any surface.
Q6: What if I miss a dose?
A: Administer the missed dose as soon as remembered, unless it is close to the next dose. Do not double the dose.
Q7: How long should the treatment last?
A: Typically, no more than two weeks for eye infections.
Q8: Can this be used for ear infections as well?
A: Yes, it can be prescribed for specific ear infections like otitis externa. Consult dosage guidelines specific to otic administration.
A: Contact lens wear should generally be avoided during treatment. Consult a doctor for further guidance.
Q10: What should I do if symptoms don’t improve or worsen?
A: Consult a doctor immediately for further evaluation and potential treatment modification.
