1. Clinical Overview
Tobramycin (0.3% w/v) is an ophthalmic solution containing a potent aminoglycoside antibiotic. It is bactericidal and is primarily used for the treatment of external ocular infections caused by susceptible strains of bacteria, particularly Pseudomonas aeruginosa, which is a major concern in the Indian context due to high rates of infection and resistance. It is a first-line agent for bacterial keratitis and blepharitis.
| Onset | Duration | Bioavailability |
|---|---|---|
| Therapeutic concentrations are achieved in the aqueous humor within 30 minutes of topical application. | Approximately 4 to 6 hours per dose, necessitating frequent application (e.g., every 4-6 hours) during active infection. | Negligible systemic bioavailability (<1%) following topical ophthalmic administration when used correctly. |
2. Mechanism of Action
Tobramycin binds irreversibly to the bacterial 30S ribosomal subunit. This binding interferes with the initiation complex, misreads mRNA, and causes premature termination of protein synthesis, leading to bacterial cell death.
3. Indications & Uses
- Treatment of external infections of the eye and its adnexa caused by susceptible bacteria.
- Bacterial Conjunctivitis
- Bacterial Keratitis (Corneal Ulcer)
- Blepharitis
- Blepharoconjunctivitis
- Dacryocystitis
4. Dosage & Administration
Adult Dosage: For mild to moderate infections: Instill 1 or 2 drops into the affected eye(s) every 4 to 6 hours. For severe infections: Instill 2 drops every hour initially, reducing frequency as infection improves.
Administration: 1. Wash hands before use. 2. Tilt head back, pull lower eyelid down to form a pouch. 3. Instill prescribed number of drops. 4. Close eyes gently for 1-2 minutes, applying gentle pressure to the nasolacrimal duct (inner corner of eye) to minimize systemic absorption. 5. Do not touch dropper tip to any surface to avoid contamination. 6. 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
- Itching or redness of the eye or eyelid
- Mild blurred vision temporarily after application
- Superficial punctate keratitis
6. Drug Interactions
| Drug | Effect | Severity |
|---|---|---|
| Other Aminoglycosides (e.g., Gentamicin, systemic) | Additive risk of nephrotoxicity and ototoxicity. | Major |
| Neuromuscular Blocking Agents (e.g., Succinylcholine, Atracurium) | Enhanced neuromuscular blockade, leading to respiratory depression. | Major |
| Loop Diuretics (e.g., Furosemide, Ethacrynic acid) | Additive risk of ototoxicity. | Major |
| Cephalosporins (systemic) | Potential additive nephrotoxicity. | Moderate |
| Vancomycin (systemic) | Increased risk of nephrotoxicity. | Moderate |
| Other Topical Ophthalmic Agents | Physical or chemical incompatibility. Administer at least 5-10 minutes apart. | Minor |
7. Patient Counselling
- DO wash hands before and after use.
- DO apply gentle pressure on the inner corner of the eye (near the nose) for 1-2 minutes after instillation.
- DO wait at least 5-10 minutes before using other eye drops.
- DO complete the full course of treatment even if symptoms improve.
- DON'T touch the dropper tip to your eye, fingers, or any surface.
- DON'T wear contact lenses while having an active infection or while using this medication unless directed by your doctor.
- DON'T share your eye drops with others.
8. Toxicology & Storage
Overdose: Topical overdose is unlikely to cause systemic symptoms. Excessive topical use may lead to severe ocular irritation, punctate keratitis, corneal edema, and increased risk of superinfection. Accidental oral ingestion may cause nausea, vomiting, and ototoxicity.
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. Discard the bottle 4 weeks after opening to prevent contamination. Keep out of reach of children.