Gentamicin topical
Gentamicin Topical
Generic Name
Gentamicin Topical
Mechanism
- Inhibition of protein synthesis
- Gentamicin binds irreversibly to the 30‑S subunit of bacterial ribosomes.
- It causes misreading of mRNA ➜ production of faulty proteins → bactericidal activity.
- High local tissue concentrations achieved through topical delivery bypass systemic barriers, ensuring rapid bacterial kill in the eye, ear canal, or skin.
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Pharmacokinetics
| Parameter | Eye Drops (0.3 %) | Ear Drops | Topical Ointment |
| Absorption | ~5–10 % of instilled dose enters systemic circulation via nasolacrimal duct | Minimal systemic absorption (<1 % of applied dose) | Negligible systemic uptake |
| Volume of distribution | Limited (ocular tissues) | Limited (aural tissues) | Local only |
| Half‑life | ~3 h (ocular) | ~1–2 h | Not applicable (topical) |
| Elimination | Urinary excretion of active parent compound | Urinary excretion | None |
| Key Limiting Factors | Perfusion of the cornea and conjunctiva, nasolacrimal drainage | Otic mucosa integrity | Skin barrier permeability |
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Indications
- Ophthalmology
- Bacterial conjunctivitis (e.g., *Staphylococcus aureus*, *Haemophilus influenzae*)
- Bacterial keratitis (in non‑graft cases)
- Post‑operative prophylaxis after ocular surgery (eye drops 5‑7 % drops 4–6 × / day for 7–15 days)
- Otolaryngology
- Otitis externa (bacterial) with or without fungal co‑infection (ear drops 3–5 × / day for 7–10 days)
- Suppurative otitis media (in combination with other therapy)
- Dermatology
- Minor abrasions, burns, and superficial skin infections (topical ointment, 24–48 h course)
- Erythema nodosum and other superficial bacterial cellulitis (when systemic therapy not feasible)
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Contraindications
- Contraindications
- Allergy to aminoglycosides or any excipient
- Severe renal impairment (if systemic absorption could be a concern, e.g., in multi‑dose topical therapy)
- Warnings
- Preserve efficacy: use undiluted formulation only for prescribed route.
- Avoid ocular contact while applying eye drops; may cause irritation.
- Can’t be used for deep or systemic infections—systemic absorption is insufficient.
- Risk of ocular surface toxicity → use only as directed; overuse may cause corneal epithelial disturbance.
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Dosing
- Eye Drops (0.3 %)
- 1–2 drops in each eye 4–6 times/day for 7–10 days.
- Avoid dilation drops; gently rinse after instillation.
- Ear Drops
- 1–3 drops in affected ear 3–5 times/day for 7–10 days.
- Keep head upright 10–15 min post‑application.
- Topical Ointment
- Apply thin layer over affected area once daily for 2–3 days (skin).
- Do not leave overnight.
- All forms: Do not exceed prescribed dosing; never mix with other eye drops or otic preparations unless advised by physician.
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Adverse Effects
| Category | Adverse Effect | Notes |
| Local | Burning, stinging, irritation (ocular or ear) | Common with topical use; transient |
| Local | Conjunctival hyperemia, keratitis | Rare, indicates hypersensitivity |
| Local | Dermal irritation (rash) | Mild; discontinue if severe |
| Systemic | Ototoxicity / nephrotoxicity | Extremely rare with topical use when limited exposure |
| Systemic | Vestibular disturbance (vertigo) | Typically from systemic absorption (rare topically) |
| Allergic | Hypersensitivity reaction (rash, itching) | Discontinue immediately |
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Monitoring
| Parameter | Frequency | Rationale |
| Ocular appearance | Daily (by clinician) | Check for redness, vision changes, corneal integrity |
| Visual acuity | At start & end of therapy | Detect optic complications; monitor recovery |
| Hearing | If used concurrently with systemic aminoglycoside | For early detection of ototoxicity |
| Renal function | If systemic absorption significant (rare) | Monitor creatinine clearance |
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Clinical Pearls
- Quick Onset: Gentamicin eye drops reach therapeutic corneal concentrations within 10–15 min; good for acute eye infections.
- Combination Strategy: When treating otitis externa with a fungal component, pair gentamicin otic drops with ketoconazole or clotrimazole to cover both pathogens.
- Avoid Irrigation: Over‑rinse the eye after instillation can reduce drug exposure; only rinse if eye irritates.
- Drug Interactions: Concomitant use of other topicals (e.g., steroid eye drops) may mask infection severity; monitor symptom changes.
- Storage: Store at 2–8 °C. Once reconstituted (for drops), keep at room temperature and use within 48 h to preserve potency.
- Patient Education: Instruct patients that transient burning is normal; advise to report any visual changes or persistent pain.
- Topical Use Safety: Due to minimal systemic absorption, gentamicin topical is safe in pregnancy and lactation, provided it's applied to the correct site and not systemic.
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