1. Clinical Overview
A sterile, topical ophthalmic solution combining the bactericidal aminoglycoside antibiotic Gentamicin with the potent corticosteroid Dexamethasone. It is primarily indicated for the treatment of steroid-responsive inflammatory ocular conditions where a risk of bacterial infection exists or where such infection is present. The combination provides anti-inflammatory, anti-allergic, and anti-infective actions.
| Onset | Duration | Bioavailability |
|---|---|---|
| Anti-inflammatory effects of dexamethasone may be observed within hours. Antimicrobial effects of gentamicin begin upon contact with susceptible bacteria. | Topical duration is approximately 4 to 6 hours per instillation, necessitating multiple daily doses. | Negligible systemic absorption following topical ocular administration in normal eyes. Absorption into the aqueous humor is variable and depends on corneal integrity. |
2. Mechanism of Action
Gentamicin binds irreversibly to the 30S ribosomal subunit of susceptible bacteria, inhibiting protein synthesis and causing bacterial cell death (bactericidal). Dexamethasone is a potent glucocorticoid that induces phospholipase A2 inhibitory proteins (lipocortins), which inhibit the release of arachidonic acid, thereby reducing the production of inflammatory mediators like prostaglandins and leukotrienes. It also suppresses migration of polymorphonuclear leukocytes and reverses increased capillary permeability.
3. Indications & Uses
- Steroid-responsive inflammatory conditions of the palpebral and bulbar conjunctiva, cornea, and anterior segment of the globe (e.g., allergic conjunctivitis, acne rosacea, superficial punctate keratitis)
- Inflammatory conditions where bacterial infection or risk of bacterial infection exists
4. Dosage & Administration
Adult Dosage: One or two drops into the conjunctival sac(s) every 4 to 6 hours. In severe disease, drops may be used hourly initially, tapering as inflammation subsides.
Administration: 1. Wash hands. 2. Tilt head back. 3. Gently pull lower eyelid to form a pouch. 4. Instill prescribed drops without touching the dropper tip to eye or any surface. 5. Close eyes gently for 1-2 minutes. Apply gentle pressure to the nasolacrimal duct (inner corner of eye) for 1 minute to minimize systemic absorption. 6. Wait at least 5-10 minutes before instilling any other ophthalmic medication. Do not wear soft contact lenses during treatment.
5. Side Effects
Common side effects may include:
- Transient burning or stinging on instillation
- Blurred vision temporarily after application
- Mild ocular irritation/itching
6. Drug Interactions
| Drug | Effect | Severity |
|---|---|---|
| Other topical ophthalmic corticosteroids | Additive risk of elevated IOP and cataract formation. | Major |
| Systemic corticosteroids (e.g., Prednisolone) | Increased systemic corticosteroid effects and side effects. | Moderate |
| Other topical aminoglycosides (e.g., Tobramycin) or systemic aminoglycosides | Potential additive ototoxicity and nephrotoxicity if significant systemic absorption occurs. | Moderate |
| Neuromuscular blocking agents (e.g., Succinylcholine) | Gentamicin may potentiate neuromuscular blockade. | Moderate |
| Loop diuretics (e.g., Furosemide) | Increased risk of ototoxicity and nephrotoxicity with systemic gentamicin. | Moderate |
7. Patient Counselling
- DO wash hands before and after use.
- DO apply gentle pressure on the inner corner of the eye for 1 minute after instillation.
- DO wait at least 5-10 minutes before using other eye drops.
- DO keep the bottle tip clean and do not let it touch anything.
- DO report any worsening symptoms, eye pain, or vision changes immediately.
- DON'T wear contact lenses during treatment unless directed by doctor.
- DON'T share your eye drops with anyone.
- DON'T stop the medication abruptly if used for more than 10 days; taper as directed.
- DON'T use the drops for any other condition or after the expiry date.
8. Toxicology & Storage
Overdose: Topical overdose is unlikely to cause systemic toxicity. Excessive use may lead to severe ocular side effects: marked elevation of IOP, severe corneal damage, exacerbation of infection. Accidental oral ingestion may cause GI upset.
Storage: Store at controlled room temperature (15°C to 25°C). Protect from light. Do not freeze. Keep the bottle tightly closed when not in use. Keep out of reach of children. Discard the bottle 4 weeks after opening to prevent contamination. Do not use if the solution is discolored or contains particles.