Gentamicin: Uses, Dosage, Side Effects and Precautions

Gentamicin is an aminoglycoside antibiotic given by injection to treat serious bacterial infections caused by susceptible bacteria. This guide covers gentamicin uses, how it works, dosage, side effects, precautions, drug interactions, use in pregnancy and breastfeeding, brand names and its approximate price in India.

At a Glance

What is Gentamicin?

Gentamicin is an aminoglycoside antibiotic. The injection is used to treat serious infections caused by susceptible bacteria, such as Pseudomonas aeruginosa, E. coli, Proteus, Klebsiella, Enterobacter, Serratia, Citrobacter and Staphylococcus. It should be used only for infections that are proven or strongly suspected to be bacterial. In suspected gram-negative infections, it may be started before culture results are ready, and continued only if tests support it. Gentamicin is not active against most streptococci (including pneumococcus) or against bacteria that live without oxygen.

How Gentamicin Works

Gentamicin is bactericidal, which means it kills bacteria. It does this by blocking normal protein making inside the bacteria. Bacteria need proteins to grow and to stay alive, so they die when they cannot make them. Gentamicin works only on bacteria, not on viruses.

When Gentamicin Is Used

• Injection: For serious bacterial infections of the blood (sepsis or septicemia), newborn sepsis, urinary tract, respiratory tract, belly (including peritonitis), skin, bone and soft tissue (including burns), and the brain and spinal cord (meningitis). Some points to know:
• Choice of antibiotic: Gentamicin is generally kept for appropriate infections caused by susceptible bacteria. The choice depends on the germ and its susceptibility, how severe the infection is, the patient’s health and the other antibiotics available.
• Urinary tract infections: The choice depends on the same factors. The US label notes that aminoglycosides are generally not indicated for uncomplicated first-time urinary infections, unless the germ is susceptible to them and not to antibiotics with less potential for toxicity.
• Meningitis: Gentamicin enters the fluid around the brain and spinal cord poorly after injection, so doctors choose treatment carefully.
• Unknown germ: In serious infections, doctors may combine it with a penicillin-type or cephalosporin antibiotic until the germ is identified.
• Eye drops: For bacterial infections of the eye, such as conjunctivitis, keratitis, corneal ulcers, blepharitis and dacryocystitis. After an injection, very little gentamicin reaches the eye, so the injection is not used for eye infections.

Your doctor decides if gentamicin is right for you.

Gentamicin Dosage and How It Is Given

The dosage details below are based on U.S. prescribing information. Approved products and instructions can differ by country, so always follow the instructions for the product your doctor prescribes. There is only a narrow gap between a helpful dose and a harmful dose of gentamicin, so the dose must be calculated and checked by the treating team. Please do not try to calculate a dose yourself.

• Injection, adults: For serious infections with normal kidney function, the label dose is 3 mg per kg per day, given in three equal doses every 8 hours. For life-threatening infections, up to 5 mg per kg per day may be used in three or four doses. It should be lowered to 3 mg per kg per day as soon as clinically possible. In clinical practice, some guidelines and hospital settings use other schedules, such as once-daily dosing. These are different from the US label regimen above, can vary by guideline, product and setting, and are decided by the treating team.
• Injection, children and newborns: The dose is based on body weight and age. Newborns, especially in the first week of life, are dosed differently. The treating team and pharmacist work it out.
• Kidney problems: Gentamicin leaves the body through the kidneys. In kidney impairment, the dose or the time between doses must be adjusted, using kidney tests and blood levels, and treatment needs close monitoring.
• Length of treatment: The usual course is 7 to 10 days. Longer courses need closer checks, because toxicity is more likely after 10 days.
• How it is given: Into a muscle or into a vein. For a vein, the injection is diluted and given as an infusion over about half an hour to two hours. It should not be mixed in the same syringe or bag with other drugs. Gentamicin should be given by trained healthcare professionals, under close clinical observation. Keeping up adequate hydration can matter during treatment when clinically appropriate. Fluid needs differ, for example in kidney disease, heart failure or fluid restriction, so follow the treating team’s instructions and do not change your fluid intake on your own.
• Eye drops (0.3%): The US label dose is 1 or 2 drops in the affected eye every 4 hours. Severe infections may need more frequent drops, only under medical supervision. This is an eye-only product and is never used as an injection. If eye symptoms get worse, see a doctor for review.

Use gentamicin only as advised by your doctor or healthcare professional. Do not start, stop, or change the dose on your own.

Side Effects of Gentamicin

• Injection: Side effects can include nausea, vomiting, headache, rash, itching, fever, decreased appetite and pain at the injection site. How often they occur is not given in the label.
• Serious side effects need medical care:
• Kidney damage: Signs can include passing less urine, or changes seen on urine and blood tests. Risk is higher with kidney disease, high doses and long treatment.
• Hearing and balance damage: It can cause dizziness, vertigo, ringing or roaring in the ears and hearing loss. This is often permanent. High-pitched hearing is usually lost first. Rarely, changes show up soon after treatment ends.
• Nerve and muscle effects: Numbness, tingling, muscle twitching and convulsions have been reported. Gentamicin can also cause muscle weakness, including weakness of the breathing muscles. This is not expected in every patient. It is a concern mainly with anesthesia or muscle relaxants, in myasthenia gravis, and in some other conditions.
• Low blood minerals: Low magnesium, calcium or potassium can cause tingling, cramps, tetany and confusion.
• Allergic reactions: Rash, swelling of the throat and anaphylactoid reactions have been reported. Some products contain sodium metabisulfite, a sulfite that can trigger allergic reactions or asthma attacks in sensitive people.
• Other effects: Changes in blood counts, overgrowth of resistant germs, and rarely a kidney tubule problem called Fanconi-like syndrome.
• Eye drops: The most common effects are burning and irritation of the eye, non-specific conjunctivitis, surface cell damage and redness. Bacterial or fungal corneal ulcers have developed during treatment, so see a doctor if the eye gets worse.

Who Should Not Use Gentamicin, and Precautions

Do not use gentamicin if you are allergic to it. A history of allergy or serious toxic reactions to other aminoglycosides may also rule it out, because allergy can cross over between them.

Risk of kidney and hearing damage is higher with kidney impairment, higher doses, longer courses, older age, dehydration, and other medicines that can harm the kidneys or ears.

• Older adults: Kidney function may be reduced even when routine blood tests look normal. A creatinine clearance test can be more useful.
• Use with care in myasthenia gravis, parkinsonism, and low blood calcium, magnesium or potassium, because gentamicin can worsen muscle weakness.
• Burns: In people with extensive burns, drug levels may be lower than expected, so doctors may check levels more closely.
• Monitoring: Doctors check kidney function (blood and urine tests), hearing and balance, and gentamicin blood levels when feasible, so that levels do not stay too high. Tell your care team at once about dizziness, vertigo, ringing in the ears, hearing change, passing less urine, numbness or muscle twitching.

Gentamicin in Pregnancy and Breastfeeding

• Pregnancy: Aminoglycosides as a group can cause fetal harm and cross the placenta. Reports of total irreversible deafness in babies exist for streptomycin, a related aminoglycoside, when it was used in pregnancy. This was reported with streptomycin and has not been shown specifically for gentamicin. For gentamicin, human data are limited. The US label says serious effects on the mother, fetus or newborn have not been reported with other aminoglycosides, and animal studies in rats and rabbits did not show harm. It is not known whether gentamicin can cause fetal harm. So there is a potential risk, and the evidence is limited. If gentamicin is used in pregnancy, or you become pregnant during treatment, your doctor should explain the possible risk and weigh the benefits and risks with you. Tell your doctor if you are pregnant or planning a pregnancy.
• Breastfeeding: Gentamicin passes into breast milk in small amounts and is poorly absorbed from the gut, so effects on the baby are thought to be unlikely. Small amounts have been found in some newborns’ blood. Talk to your doctor. The baby may be watched for gut effects such as loose stools. Eye drops are considered to pose little or no risk to a nursing baby.

Gentamicin Interactions and Other Medicines

• Other medicines that can harm the kidneys or ears: Examples are cisplatin, other aminoglycosides (amikacin, tobramycin, streptomycin, kanamycin, neomycin), polymyxin B, colistin and vancomycin. Using them together with gentamicin, at the same time or one after another, can raise the risk of kidney or hearing damage. Depending on the clinical situation, the treating team may avoid the combination, adjust the doses or monitor closely.
• Strong diuretics (water pills): Furosemide and ethacrynic acid can harm hearing by themselves, and given into a vein they can raise gentamicin toxicity. The US label advises avoiding the combination, and the treating team decides based on the situation.
• Cephalosporins: Using them together with gentamicin may increase the risk of kidney toxicity. Not everyone who receives both medicines develops kidney damage. Clinicians consider your kidney function, whether both are needed and how closely to monitor.
• Anesthetics and muscle relaxants: Examples are succinylcholine and tubocurarine. Gentamicin can add to their effect on the muscles, including breathing muscles. Large transfusions of citrated blood carry a similar risk. Care teams are aware of this and plan accordingly.
• Penicillin-type antibiotics: They are sometimes used together on purpose, but they should not be mixed in the same syringe or bag. In severe kidney impairment, carbenicillin can shorten gentamicin’s half-life.

This list is not complete. Tell your doctor and pharmacist about all prescription medicines, over-the-counter medicines, vitamins and herbal products you use.

Gentamicin Brands in India

Examples of brands available in India include:

1. Garamycin (Fulford): an 80 mg per 2 mL injection.
2. Genticyn injection (Abbott): an 80 mg per 2 mL injection.
3. Genticyn eye drops (Abbott): 0.3% eye drops, for the eye only.
4. Genticyn B eye drops: a different combination product that also contains a steroid (betamethasone). It is not the same as Genticyn eye drops.

Gentamicin itself is the generic name, not a brand. This list is not complete. Brand availability, strength, formulation and pack size can change, so please verify the current product information with a licensed pharmacy or healthcare professional.

Gentamicin Price in India

The prices below are approximate maximum retail prices (MRP) as shown on online pharmacy listings. They may have changed, may not be current, and vary by brand, strength, formulation, pack size, pharmacy and location. Hospital charges for the injection can differ. Please check the current price with a licensed pharmacy.

Garamycin 80 mg per 2 mL injection (Fulford), one vial: roughly Rs 7 to Rs 9.

Genticyn 80 mg per 2 mL injection (Abbott), one vial: roughly Rs 9 to Rs 10.50.

Genticyn 0.3% eye drops (Abbott), 5 mL bottle: roughly Rs 9. Listed MRPs range from about Rs 8.80 to Rs 9.40.

Genticyn 0.3% eye drops (Abbott), 10 mL bottle: roughly Rs 9.50 to Rs 10. Listings for the 5 mL and 10 mL packs show similar prices, so please confirm the pack size with the pharmacy.

How HealthPil Can Help

Medicines should be started, adjusted, or stopped only under the guidance of a qualified healthcare professional. If you have questions about gentamicin, its side effects, or your treatment plan, you can consult a doctor, such as an infectious disease specialist, through HealthPil.