Gentamicin (0.3% w/v) is a topical ophthalmic/otic formulation of a broad-spectrum aminoglycoside antibiotic. It is bactericidal and is primarily used for the treatment of superficial bacterial infections of the eye and external ear canal. It is effective against a wide range of Gram-negative bacteria (including Pseudomonas aeruginosa) and some Gram-positive bacteria. In the Indian context, it is a first-line, cost-effective option for bacterial conjunctivitis, blepharitis, and otitis externa.
Adult: **Ophthalmic:** Instill 1-2 drops into the affected eye(s) every 4 to 6 hours. For severe infections, may be used hourly initially, tapering as infection improves. **Otic:** Instill 3-4 drops into the affected ear 3-4 times daily.
Note: **Eye Drops:** Wash hands. Tilt head back, pull lower eyelid down to form a pouch. Instill drops without touching dropper to eye or any surface. Close eye gently for 1-2 minutes, apply gentle pressure to the nasolacrimal duct (inner corner of eye) to minimize systemic absorption. **Ear Drops:** Lie on side with affected ear upward. Pull the auricle upward and backward (in adults) to straighten the ear canal. Instill drops. Remain in position for 5 minutes. Do not insert any device into the ear. Use sterile cotton plug if needed.
Gentamicin binds irreversibly to the 30S ribosomal subunit of susceptible bacteria. This binding interferes with the initiation complex and causes misreading of the mRNA template, leading to the incorporation of incorrect amino acids into the growing polypeptide chain. This results in the production of non-functional or toxic proteins and ultimately bacterial cell death.
Pregnancy: **Category D (US FDA).** Aminoglycosides cross the placenta. Risk of fetal ototoxicity exists with systemic use. Topical use is generally considered acceptable when benefits outweigh risks, as systemic absorption is minimal. Use only if clearly needed and under medical supervision.
Driving: May cause transient blurred vision immediately after ophthalmic instillation. Patients should not drive or operate machinery until vision clears.
| Other Ototoxic Drugs (e.g., IV Furosemide, Cisplatin) | Increased risk of hearing loss or vestibular damage. | Major |
| Other Nephrotoxic Drugs (e.g., IV Vancomycin, NSAIDs, Amphotericin B) | Increased risk of kidney damage if systemically absorbed. | Moderate |
| Neuromuscular Blocking Agents (e.g., Succinylcholine, Vecuronium) | Potentiation of neuromuscular blockade, leading to prolonged apnea. | Major |
| Other Topical Corticosteroids (e.g., Dexamethasone, Prednisolone) | May mask signs of infection or potentiate spread of infection. Combined formulations are used judiciously. | Moderate |