neomycin

neomycin is an aminoglycoside antibiotic discovered from the soil bacterium Streptomyces fradiae. It is primarily used topically due to significant ototoxicity and nephrotoxicity when administered systemically. Its development was a significant milestone in the antibiotic era, following the discoveries of penicillin and streptomycin.

Medical uses

It is commonly formulated in topical creams, ointments, and eye drops for treating superficial infections caused by susceptible Gram-negative and some Gram-positive bacteria. Typical applications include preventing infection in minor cuts, burns, and abrasions, and it is a key component in many over-the-counter first aid preparations. It is also used orally for hepatic encephalopathy to reduce ammonia-producing gut flora and is employed in bowel preparation before colorectal surgery. In veterinary medicine, it is used to treat infections in animals like cattle and poultry.

Adverse effects

The most serious adverse effects are ototoxicity, which can lead to irreversible hearing loss and vestibular dysfunction, and nephrotoxicity, potentially causing acute kidney injury. These risks severely limit its parenteral use. Topical application can cause contact dermatitis and skin irritation, while oral use may result in nausea, vomiting, and diarrhea. Prolonged use can lead to superinfection with resistant organisms like *Clostridioides difficile* or fungi. The Food and Drug Administration has issued warnings about its potential for serious allergic reactions.

Mechanism of action

It binds irreversibly to the bacterial 30S ribosomal subunit, specifically to the 16S rRNA component within the A site of the ribosome. This binding interferes with the initiation complex during protein synthesis and causes misreading of messenger RNA, leading to the incorporation of incorrect amino acids and the production of nonfunctional or toxic polypeptides. This bactericidal action is concentration-dependent and is most effective against aerobic organisms, as its uptake into bacterial cells is an oxygen-dependent active process.

History

It was discovered in 1949 by Selman Waksman and his colleague Hubert Lechevalier at Rutgers University, following Waksman's earlier Nobel Prize-winning work on streptomycin. The discovery was part of a systematic screening program of soil actinomycetes at the Waksman Institute of Microbiology. Its development was commercialized by Merck & Co., and it received approval from the Food and Drug Administration in the early 1950s. Its introduction provided a broader-spectrum alternative to earlier antibiotics, though its systemic toxicity soon became apparent.

Society and culture

It is widely available in numerous generic formulations and is a staple in over-the-counter topical antibiotic combinations, often paired with polymyxin B and bacitracin in products like Neosporin. Its role in animal husbandry for growth promotion and disease prevention has been scrutinized, contributing to concerns about antibiotic resistance and leading to regulatory changes by agencies like the World Health Organization. It has been referenced in popular culture, including episodes of the television series *M*A*S*H* and in discussions about the antibiotic era in documentaries.