An aminoglycoside antibiotic
Gentamicin
A powerful aminoglycoside antibiotic, usually given by injection in hospital for serious infections.
What is Gentamicin?
Gentamicin is a strong aminoglycoside antibiotic used mainly in hospital, usually given by injection or drip, to treat serious bacterial infections. It is very effective but can harm hearing and balance (ototoxic) and the kidneys (nephrotoxic), so blood levels and kidney function are closely monitored. It is also available as eye and ear drops for local infections.
Education and reference only. This is a plain-language guide to Gentamicin — it deliberately contains no doses. Doses depend on the person, the brand and the reason for treatment, and belong with your prescriber. Always check the BNF, the product labelling (SmPC) and follow medical advice.
What it is
Gentamicin is a powerful aminoglycoside antibiotic used chiefly for serious bacterial infections — such as those affecting the blood, urinary tract, abdomen or chest — and often as part of treatment for sepsis. Because it is not absorbed well from the gut, it is usually given by injection or a drip in hospital, where it can be monitored carefully. It is also made as eye and ear drops for local infections, and is sometimes used in combination with other antibiotics.
How it works
Gentamicin attacks bacteria by getting inside them and binding to their ribosomes — the tiny factories where the bacteria build the proteins they need to survive. By jamming this protein-making machinery, gentamicin stops the bacteria functioning and kills them. It is especially active against certain serious 'Gram-negative' bacteria. The same medicine can, however, build up in the inner ear and kidneys, which is why it can affect hearing, balance and kidney function and needs careful monitoring.
Company & origin
Originated / developed by: Available as a generic medicine from several manufacturers..
First discovered in the 1960s, gentamicin remains a mainstay aminoglycoside antibiotic in UK hospitals.
Practical use
How to take Gentamicin
General, dose-free guidance — always follow your prescriber's and the leaflet's specific instructions.
- It is usually given by injection or a drip by healthcare staff in hospital.
- Tell staff straight away if you notice ringing in the ears, hearing changes, dizziness or unsteadiness.
- Blood tests for drug levels and kidney function are taken to guide treatment — these are an important part of care.
- Stay well hydrated unless told otherwise, as this helps protect the kidneys.
- For eye or ear drops, use them exactly as directed and complete the prescribed course.
Weighing it up
Advantages & disadvantages of Gentamicin
Advantages
- Very effective against serious infections, including some that resist other antibiotics.
- Works quickly and is valuable in treating sepsis and other life-threatening infections.
- Available as eye and ear drops for local infections with much lower risk.
Disadvantages
- Can permanently harm hearing and balance (ototoxic), sometimes without early warning.
- Can damage the kidneys (nephrotoxic), so needs blood-level and kidney monitoring.
- Usually has to be given by injection in hospital rather than taken at home as tablets.
Practical use
Good to know
Gentamicin is a hospital antibiotic that needs close supervision. Its two main safety concerns are damage to hearing and balance (it is ototoxic — report any ringing in the ears, hearing changes, dizziness or unsteadiness) and damage to the kidneys (it is nephrotoxic). To manage this, blood levels of the drug and kidney function are checked during treatment, and the dose and timing are adjusted accordingly. Courses are usually kept as short as the infection allows. Eye and ear drop forms act locally and carry far less of these risks.
Who should not take it / use with caution
- People who have had a serious allergic reaction to gentamicin or other aminoglycosides.
- Used with great caution in significant kidney problems and in people with existing hearing or balance disorders.
- Care is needed in pregnancy and in older people. Avoided in people with myasthenia gravis unless there is no alternative, because it can dangerously worsen muscle weakness.
Monitoring
- Blood levels of gentamicin to keep them in a safe range
- Kidney function (blood tests) before and during treatment
- Hearing and balance, especially with longer courses
Side effects
- Damage to hearing or balance — report ringing in the ears, hearing loss, dizziness or unsteadiness.
- Effects on the kidneys, picked up through blood and urine monitoring.
- With drops, local stinging or irritation of the eye or ear.
Key interactions
- Other medicines that can harm the kidneys or hearing add to the risk and need careful review.
- Strong diuretics ('water tablets') such as furosemide can increase the risk of hearing damage.
- It can affect how some muscle-relaxant medicines used in anaesthesia work.
Available as: Injection, eye drops and ear drops.
Answers
Gentamicin: frequently asked questions
Why is gentamicin given by injection rather than tablets?
Gentamicin is barely absorbed from the gut, so it would not work as a tablet for a body-wide infection. It is given by injection or a drip, usually in hospital, where its levels and effects can be monitored.
Why do I need blood tests while on gentamicin?
Blood tests check the level of the drug and how your kidneys are coping. Keeping the level in the right range protects your hearing and kidneys while making sure there is enough to treat the infection.
Can gentamicin affect my hearing?
Yes — it can affect hearing and balance, which is why it is monitored carefully. Report any new ringing in the ears, hearing changes, dizziness or unsteadiness to the team straight away.
Are gentamicin eye or ear drops as risky as the injections?
No. Drops act locally on the eye or ear and very little reaches the rest of the body, so the risks to hearing and kidneys are far lower. Use them as directed and finish the course.
Is gentamicin a strong antibiotic?
Yes, it is a powerful antibiotic reserved largely for serious infections, including sepsis, and is often used in hospital. Its strength is matched by the need for close monitoring to use it safely.
The wider class
About Aminoglycosides
Gentamicin belongs to the aminoglycosides class. For how the class as a whole works, its shared safety principles and monitoring, see the full guide.
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Authoritative sources
- BNF: Gentamicin.
- NICE CKS: Antibiotics.
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