1. Clinical Overview
A sterile, topical ophthalmic suspension/ointment combining a potent corticosteroid (Dexamethasone) with a broad-spectrum aminoglycoside antibiotic (Tobramycin). It is primarily indicated for the treatment of steroid-responsive inflammatory ocular conditions where the risk of superficial bacterial infection is high or where such an infection already exists. This combination provides anti-inflammatory, anti-allergic, and antibacterial actions.
| Onset | Duration | Bioavailability |
|---|---|---|
| Anti-inflammatory effects begin within hours; antibacterial effects begin immediately upon contact with susceptible organisms. | Topical ocular duration is approximately 4 to 8 hours per dose, necessitating multiple daily applications. | Negligible systemic absorption following topical ocular administration in the presence of an intact corneal epithelium. Absorption into the aqueous humor is minimal. |
2. Mechanism of Action
Dexamethasone exerts potent anti-inflammatory, anti-allergic, and anti-proliferative effects by inducing phospholipase A2 inhibitory proteins (lipocortins), which control the biosynthesis of potent mediators of inflammation like prostaglandins and leukotrienes. It suppresses migration of polymorphonuclear leukocytes and reverses increased capillary permeability. Tobramycin is a bactericidal aminoglycoside that binds irreversibly to the 30S ribosomal subunit of susceptible bacteria, inhibiting protein synthesis and causing misreading of the genetic code.
3. Indications & Uses
- Steroid-responsive inflammatory ocular conditions with a risk of or presence of superficial bacterial infection.
- Post-operative ocular inflammation following cataract surgery or other intraocular procedures where infection prophylaxis is desired.
- Blepharitis, conjunctivitis, and keratitis of mixed inflammatory and suspected bacterial etiology.
4. Dosage & Administration
Adult Dosage: Suspension: Instill 1 or 2 drops into the conjunctival sac(s) every 4 to 6 hours. In severe disease, may be used hourly initially, tapering as inflammation subsides. Ointment: Apply a small ribbon (approx. 1 cm) into the conjunctival sac up to 3-4 times daily.
Administration: Shake suspension well before use. Wash hands. Tilt head back, pull lower eyelid down to form a pouch. Instill drops/apply ointment without touching the tip to the eye or any surface. Close eye gently for 1-2 minutes. Apply gentle pressure to the nasolacrimal duct (inner corner of eye) for 1 minute to reduce systemic absorption. Wait at least 5-10 minutes before instilling any other ophthalmic medication.
5. Side Effects
Common side effects may include:
- Transient ocular burning or stinging upon instillation
- Blurred vision (especially with ointment)
- Foreign body sensation
- Mild conjunctival hyperemia
- Itching
6. Drug Interactions
| Drug | Effect | Severity |
|---|---|---|
| Other Aminoglycosides (systemic or topical) | Increased risk of ototoxicity and nephrotoxicity (additive). | Moderate |
| Systemic Corticosteroids | Additive systemic steroid effects, increasing risk of hypercortisolism. | Moderate |
| Neuromuscular Blocking Agents (e.g., Succinylcholine) | Tobramycin may potentiate neuromuscular blockade, leading to respiratory depression. | Major |
| Loop Diuretics (e.g., Furosemide) | Increased risk of ototoxicity when combined with tobramycin. | Moderate |
| Cyclosporine | Concurrent use may increase risk of cataract formation. | Moderate |
7. Patient Counselling
- DO shake the suspension well before use.
- DO wash hands before and after use.
- DO apply pressure on the inner corner of the eye for a minute after instillation.
- DO NOT touch the dropper tip to your eye, fingers, or any surface.
- DO NOT wear contact lenses during treatment unless advised by doctor (preservative can be absorbed).
- DO NOT stop the medication abruptly if used for more than 10 days; taper as directed.
- DO NOT use for any condition other than prescribed.
8. Toxicology & Storage
Overdose: Topical overdose is unlikely to cause acute systemic toxicity. Accidental oral ingestion may cause GI upset. Excessive topical application may lead to severe ocular side effects: severe elevation of IOP, corneal damage, severe infection.
Storage: Store at controlled room temperature (15°C to 25°C). Protect from light. Do not freeze. Keep the container tightly closed. Keep out of reach of children. Discard the suspension/ointment 4 weeks after opening the bottle/tube. Do not use if the suspension is discolored or contains particles.