What is the Use of Neomycin? Exploring Its Diverse Applications

October 6, 2025 •

4 min read

First discovered in 1949, neomycin is a broad-spectrum aminoglycoside antibiotic derived from the bacterium Streptomyces fradiae. Its use is primarily limited to topical, otic, and certain oral applications due to significant potential for systemic toxicity, distinguishing its use of neomycin from other antibiotics.

Quick Summary

Neomycin is an aminoglycoside antibiotic used topically for minor skin infections, in ear drops for outer ear infections, and orally for bowel preparation before surgery and to manage hepatic encephalopathy. Poorly absorbed orally, its systemic use is limited by potential ototoxicity and nephrotoxicity.

Key Points

Hepatic Encephalopathy: Oral neomycin is used to reduce ammonia-producing gut bacteria and manage the symptoms of this liver-related neurological condition.
Bowel Preparation: As part of a pre-operative regimen, oral neomycin is administered before bowel surgery to decrease the risk of post-operative infection.
Topical Skin Infections: Neomycin is a common ingredient in over-the-counter ointments, like Neosporin, to prevent and treat minor skin infections from cuts and scrapes.
Ear and Eye Infections: It is used in combination with other antibiotics and steroids in ear drops for outer ear infections and ophthalmic preparations for specific eye infections.
Limited Systemic Use: Due to the high risk of ototoxicity (hearing loss) and nephrotoxicity (kidney damage), neomycin is rarely used systemically and is primarily restricted to its poorly-absorbed oral and topical forms.
Combination Therapy: Neomycin is often formulated with other agents like polymyxin B, bacitracin, or hydrocortisone to enhance its broad-spectrum efficacy and manage inflammation.

Overview of Neomycin

Neomycin is an antibiotic that works by inhibiting bacterial protein synthesis, a critical function for bacterial survival. It is part of the aminoglycoside class and is active against a range of bacteria, including gram-negative and some gram-positive strains. While it was once considered for broader systemic use, severe side effects like damage to the kidneys (nephrotoxicity) and inner ear (ototoxicity), including irreversible hearing loss, have restricted its modern application. Consequently, its use is now largely confined to formulations where systemic absorption is minimal.

Oral Use: Targeting the Gastrointestinal Tract

Due to its poor absorption from the gastrointestinal tract, neomycin is uniquely suited for treating conditions within the digestive system. In these scenarios, it works locally within the gut to reduce the bacterial population responsible for producing harmful substances.

Hepatic Encephalopathy

Hepatic encephalopathy is a neurological complication of liver disease, where the liver fails to properly remove toxins from the blood. These toxins, primarily ammonia produced by bacteria in the gut, can affect brain function. Oral neomycin is used to address this by targeting and reducing the ammonia-producing bacteria in the intestines, thereby helping to lessen the symptoms of this condition.

Bowel Preparation for Surgery

Before certain surgical procedures, especially those involving the bowels (colorectal surgery), patients undergo a bowel prep regimen to reduce the risk of infection. Neomycin is a key component in this process, typically administered orally in combination with other antibiotics like erythromycin or metronidazole. By significantly reducing the bacteria in the gut, it helps prevent surgical site infections.

Topical Use: Skin Infections

Neomycin is a common ingredient in many over-the-counter topical antibiotic products designed to prevent and treat minor skin infections. Its application is intended for external use only on minor cuts, scrapes, and burns to kill bacteria and prevent contamination. Topical neomycin is often formulated in combination products to increase its broad-spectrum effectiveness.

Common Combination Products: You can find neomycin in a variety of triple antibiotic ointments and creams. These typically combine neomycin, bacitracin, and polymyxin B.
How to Apply: The medication is applied in a thin film to the cleaned affected area, often 1 to 3 times a day.

Otic and Ophthalmic Use: Eyes and Ears

For localized infections of the eye and ear, neomycin is formulated into solutions and suspensions, usually combined with other agents.

Ear Infections: For outer ear infections, or 'swimmer's ear,' neomycin is combined with antibiotics like polymyxin B and a steroid like hydrocortisone. The antibiotics target the bacterial infection, while the steroid reduces the associated inflammation, swelling, and itching.
Eye Infections: Ophthalmic preparations containing neomycin, often with polymyxin B and dexamethasone, are used to treat inflammatory eye conditions where a bacterial infection is present or at risk.

Comparison of Neomycin with Gentamicin

Both neomycin and gentamicin are aminoglycoside antibiotics that inhibit bacterial protein synthesis, but they have distinct applications and risk profiles.


Feature	Neomycin	Gentamicin
Spectrum	Broader initial spectrum, but more susceptible to resistance; strong against gram-negative bacteria, some gram-positive.	Broad spectrum, effective against many gram-negative, including Pseudomonas aeruginosa, and some gram-positive strains.
Absorption	Poorly absorbed orally; effective for localized gut treatment.	Better absorbed systemically; typically administered via injection for serious infections.
Primary Use	Oral for hepatic encephalopathy and bowel prep; Topical for skin; Otic/Ophthalmic for localized infections.	Systemic use for more serious, systemic infections like sepsis or pneumonia.
Toxicity Risk	High risk of ototoxicity and nephrotoxicity with systemic absorption; risk is low with topical or oral use due to minimal absorption.	Also carries risks of ototoxicity and nephrotoxicity, requiring careful monitoring, especially during long-term therapy.

Potential Side Effects and Precautions

Neomycin is not without risks, which is why its usage is carefully managed. The most significant risks are associated with systemic absorption, which is why oral and topical formulations must be used with caution, especially on large surface areas or broken skin where absorption can occur.

Ototoxicity: Neomycin can cause damage to the inner ear, leading to hearing loss and balance issues, which can be permanent. This risk is heightened in older patients or those with kidney problems.
Nephrotoxicity: Kidney damage is another potential adverse effect, especially with prolonged use or impaired renal function.
Allergic Reactions: Topical application can lead to allergic reactions, causing skin irritation, redness, and rash.
Cautions: Use of neomycin should be avoided in patients with known allergies to aminoglycosides, pre-existing kidney disease, or hearing impairment.

Conclusion

While systemic use of neomycin is largely avoided due to serious side effects, its localized applications remain important in modern medicine. The medication's limited absorption when taken orally or applied topically makes it a targeted and effective treatment for specific conditions like hepatic encephalopathy, pre-surgical bowel preparation, and localized skin, ear, and eye infections. However, its use requires careful consideration of the potential for toxicity, particularly with long-term use, and is often reserved for situations where its benefits outweigh the risks.

For more detailed information, consult the StatPearls article on Neomycin.

Frequently Asked Questions

Neomycin is an aminoglycoside antibiotic that works by interfering with the synthesis of bacterial proteins. Specifically, it binds to the 30S ribosomal subunit of bacteria, disrupting the protein-making process and ultimately killing the bacteria.

No, neomycin is only effective against bacterial infections and will not work for viral or fungal infections. Furthermore, due to its toxicity, its use is limited to specific applications, and it should not be used without a healthcare provider's guidance.

Oral neomycin is used for conditions within the gut, such as hepatic encephalopathy and bowel prep, because it is poorly absorbed by the body. Topical neomycin is applied directly to the skin to treat or prevent minor surface-level bacterial infections.

Neosporin is a brand name for a common triple antibiotic ointment that contains neomycin, along with bacitracin and polymyxin B. While Neosporin contains neomycin, they are not the same; neomycin is a single antibiotic, whereas Neosporin is a combination product.

The most serious side effects, associated with systemic absorption, include ototoxicity (damage to hearing and balance) and nephrotoxicity (kidney damage). Topical use can cause localized allergic reactions like skin irritation or rash.

Because of its significant potential for causing severe and often irreversible ototoxicity and nephrotoxicity, neomycin's use is restricted to conditions where its absorption into the bloodstream is minimal. For more serious systemic infections, less toxic antibiotics are preferred.

Use during pregnancy is a concern due to reports of irreversible congenital deafness in newborns whose mothers were exposed to a related aminoglycoside, streptomycin. The potential risks to the fetus should be discussed with a healthcare provider if pregnancy is a possibility.