Gentamicin

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Gentamicin on Prescriptsy

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Gentamicin is an aminoglycoside antibiotic used topically to treat bacterial infections of the ear and eye.

It is available as gentamicin 0.3% ear drops, gentamicin 0.3% eye drops, and gentamicin 0.3% eye ointment.

Gentamicin has broad-spectrum activity against many Gram-negative and some Gram-positive bacteria, including Pseudomonas aeruginosa and Staphylococcus aureus, making it a valuable treatment for common ear and eye infections.

Gentamicin ear and eye drops are prescription-only medicines (POM) in the United Kingdom.

This page provides a comprehensive clinical overview of topical gentamicin, including how it works, what conditions it treats, how to use it, potential side effects, important safety warnings, and how to obtain a prescription in the UK.

Important safety information about gentamicin

• Gentamicin ear and eye drops are prescription-only medicines (POM) that should be used only as directed by a prescriber.
• Do not use gentamicin ear drops if you have a perforated eardrum unless your doctor has specifically assessed and approved this.
• Do not use topical gentamicin for longer than 14 days without medical review.
• Remove contact lenses before using gentamicin eye drops and wait at least 15 minutes before reinserting them.
• Discard opened eye drop bottles after 4 weeks.

Understanding ear and eye infections

Otitis externa (outer ear infection) is one of the most common conditions seen in UK general practice, particularly during the summer months when swimming increases the risk of water-borne bacteria entering the ear canal.

It presents with ear pain, itching, discharge, and sometimes reduced hearing if the ear canal becomes swollen or blocked with debris.

The ear canal skin becomes inflamed and infected, most commonly by Pseudomonas aeruginosa or Staphylococcus aureus.

Risk factors include frequent swimming, use of cotton buds or ear plugs, hearing aid use, eczema or psoriasis affecting the ear canal, and narrow ear canals.

Most cases are mild to moderate and respond well to topical antibiotic and antiseptic ear drops.

Bacterial conjunctivitis is infection of the conjunctiva (the transparent membrane covering the white of the eye and the inner surface of the eyelids).

It typically causes redness, a gritty sensation, discharge (often purulent, sticking the eyelids together on waking), and mild discomfort.

It is usually caused by Staphylococcus aureus, Streptococcus pneumoniae, or Haemophilus influenzae.

While many cases of bacterial conjunctivitis are self-limiting, topical antibiotics reduce the duration and severity of symptoms and limit the spread of infection to others, which is particularly important in schools and childcare settings.

How gentamicin works: mechanism of action

Gentamicin belongs to the aminoglycoside class of antibiotics. It exerts its antibacterial effect by binding irreversibly to the 30S ribosomal subunit inside susceptible bacteria.

The bacterial ribosome is the cellular machinery responsible for translating genetic information (messenger RNA) into proteins.

By binding to the ribosome, gentamicin causes the bacterial protein synthesis machinery to misread the mRNA code, resulting in the production of abnormal, non-functional proteins.

These faulty proteins are incorporated into the bacterial cell membrane, disrupting its integrity and leading to leakage of cellular contents and cell death.

This mechanism makes gentamicin bactericidal, meaning it actively kills bacteria rather than merely stopping their growth.

Bactericidal activity is an advantage in treating infections, as it does not rely on the immune system to clear non-replicating organisms.

Gentamicin also demonstrates a post-antibiotic effect: bacterial killing continues for several hours after the drug concentration falls below the minimum inhibitory concentration, because the irreversible binding to ribosomes continues to disrupt protein synthesis even after the drug is cleared.

Gentamicin has excellent activity against most aerobic Gram-negative bacteria, including Pseudomonas aeruginosa (a particularly important pathogen in otitis externa), Escherichia coli, Klebsiella pneumoniae, Proteus mirabilis, and Enterobacter species.

It also has useful activity against Staphylococcus aureus, including some methicillin-sensitive strains. It has limited activity against streptococci and anaerobic bacteria.

When applied topically to the ear canal or conjunctival sac, gentamicin achieves high local concentrations at the site of infection while causing negligible systemic absorption.

Clinical evidence and UK prescribing guidance

Topical aminoglycosides, including gentamicin, have been used for the treatment of ear and eye infections for decades and have an extensive clinical track record.

NICE Clinical Knowledge Summaries on otitis externa recommend topical antibiotic ear drops, often combined with a topical corticosteroid to reduce inflammation, as the mainstay of treatment for uncomplicated acute otitis externa.

Gentamicin ear drops (alone or in combination with hydrocortisone) are listed in the BNF as a suitable option.

For bacterial conjunctivitis, NICE Clinical Knowledge Summaries advise that while many cases resolve without treatment, topical antibiotics may be offered to reduce symptom duration and infectivity.

Chloramphenicol eye drops (available over the counter as a pharmacy medicine) are the most commonly used first-line treatment in UK primary care.

Gentamicin eye drops are an alternative, particularly when chloramphenicol is unsuitable or when broader Gram-negative cover is required, such as in suspected Pseudomonas conjunctivitis or in contact lens-related infections.

The BNF notes that aminoglycoside eye drops, including gentamicin, are useful for acute infections and are often the first choice in ophthalmic units for more serious bacterial keratitis (corneal infection), where they may be used in fortified concentrations prepared by hospital pharmacies.

For routine conjunctivitis in primary care, standard 0.3% gentamicin eye drops are prescribed.

Gentamicin compared with other topical antibiotics

For ear infections, the main alternatives to gentamicin ear drops include ciprofloxacin ear drops (a fluoroquinolone with excellent Pseudomonas coverage and no ototoxic risk, making it the preferred option when tympanic membrane perforation is known or suspected), neomycin-containing ear drops (often combined with corticosteroids, but with a higher risk of contact sensitivity), and acetic acid 2% spray (an antiseptic option for mild otitis externa that avoids antibiotic resistance concerns entirely).

For eye infections, chloramphenicol 0.5% eye drops are the most widely used first-line treatment in the UK and have the advantage of being available as a pharmacy (P) medicine for adults.

Fusidic acid 1% viscous eye drops (Fucithalmic) are used for staphylococcal conjunctivitis and have the convenience of twice-daily dosing.

Gentamicin eye drops offer broader Gram-negative coverage than either chloramphenicol or fusidic acid, making them particularly useful for infections where Pseudomonas or other resistant Gram-negative organisms are suspected.

The choice of topical antibiotic depends on the suspected causative organism, the site and severity of infection, the integrity of the tympanic membrane (for ear infections), patient allergies, and local resistance patterns.

Your prescriber will select the most appropriate preparation based on clinical assessment.

Dosage and administration

For otitis externa, apply 2 to 3 drops of gentamicin 0.3% ear drops into the affected ear three to four times daily.

Lie on your side with the affected ear uppermost, instil the drops, and remain still for 5 minutes.

Treat for 7 days, or up to 14 days if clinically indicated.

For bacterial conjunctivitis, instil 1 to 2 drops of gentamicin 0.3% eye drops every 2 hours while awake for the first 48 hours, then reduce to four times daily.

Continue for 48 hours after the eye appears normal.

Eye ointment may be applied at bedtime if drops are used during the day, or 2 to 3 times daily if used as monotherapy.

Wash your hands before and after applying ear or eye drops. Avoid touching the dropper tip to any surface, including the ear, eye, or skin.

For eye drops, tilt the head back, pull down the lower eyelid, and instil the drop into the pocket formed.

Close the eye gently and press on the inner corner (near the nose) for 1 to 2 minutes to reduce systemic drainage.

Side effects of topical gentamicin

Common side effects

Mild burning, stinging, or irritation at the application site is the most frequently reported effect. With eye drops, temporary blurred vision may occur. These effects are transient and usually settle within minutes.

Uncommon and rare side effects

Allergic reactions including localised redness, itching, and swelling may occur. Contact dermatitis has been reported, particularly with ear preparations.

Prolonged use may lead to superinfection with resistant bacteria or fungi. Ototoxicity is a rare but important risk if ear drops pass through a perforated tympanic membrane.

When to seek medical advice

Contact your GP or call NHS 111 if your symptoms worsen during treatment, if new symptoms develop (increased pain, hearing loss, visual disturbance), or if the infection has not improved after 7 days.

Seek immediate help (call 999) if you develop signs of a severe allergic reaction including difficulty breathing or swelling of the face, lips, or throat.

Report suspected adverse reactions to the MHRA via the Yellow Card scheme at yellowcard.mhra.gov.uk .

Warnings and precautions

Do not use gentamicin if you are allergic to gentamicin, other aminoglycosides (neomycin, tobramycin, amikacin), or any ingredient in the formulation.

Exercise particular caution with ear drops if the eardrum is perforated. Do not use for longer than 14 days without review. Remove contact lenses before using eye drops.

Discard eye drop bottles 4 weeks after opening.

There are no clinically significant systemic drug interactions with topical gentamicin at recommended doses. Inform your prescriber if you are receiving systemic aminoglycosides or other ototoxic/nephrotoxic medicines.

Topical gentamicin can be used in pregnancy and breastfeeding when clinically indicated. Temporary blurred vision after eye drops may affect driving.

How to get gentamicin ear or eye drops in the UK

Gentamicin ear and eye drops are prescription-only medicines. Your GP can prescribe them following clinical assessment of your ear or eye infection.

For eye infections, some optometrists (opticians with therapeutic qualifications) can also prescribe gentamicin eye drops under independent prescriber arrangements.

Authorised online prescribers registered with the General Pharmaceutical Council (GPhC) can prescribe following an appropriate consultation.

The NHS prescription charge in England is currently 9.90 pounds per item; prescriptions are free in Scotland, Wales, and Northern Ireland.

Preventing ear and eye infections

To reduce the risk of otitis externa, dry your ears thoroughly after swimming or bathing by tilting the head to each side and gently pulling the ear lobe in different directions.

Do not insert cotton buds or other objects into the ear canal, as this damages the protective skin lining and pushes wax deeper.

Consider using ear plugs or a swimming cap when swimming, particularly if you are prone to ear infections.

If you wear hearing aids, ensure they are cleaned regularly and allow your ears to air between periods of use.

To prevent bacterial conjunctivitis, wash your hands frequently and avoid touching your eyes. Do not share towels, flannels, pillows, or eye cosmetics with others.

Replace eye cosmetics (mascara, eyeliner) every 3 months. If you wear contact lenses, follow your optician's advice on cleaning, storage, and replacement schedules.

Do not sleep in contact lenses unless specifically designed for extended wear. Treat any underlying conditions such as blepharitis (eyelid margin inflammation) that may predispose to recurrent conjunctivitis.

Sources

• Gentamicin 0.3% Eye/Ear Drops, Summary of Product Characteristics (EMC)
• Gentamicin, British National Formulary (BNF)
• NICE CKS: Otitis externa
• NICE CKS: Conjunctivitis, infective
• Ear infections, NHS
• Conjunctivitis, NHS
• MHRA Yellow Card Scheme