Neomycin

Neomycin is an aminoglycoside antibiotic found in many topical medications such as creams, ointments, and eyedrops. Neomycin belongs to aminoglycoside class of antibiotics that contain two or more amino sugars connected by glycosidic bonds. Neomycin is an aminoglycoside antibiotic found in many topical medications such as creams, ointments, and eyedrops. Neomycin belongs to aminoglycoside class of antibiotics that contain two or more amino sugars connected by glycosidic bonds. The discovery of neomycin dates back to 1949. It was patented in 1950 and approved for medical use in 1952. Neomycin is typically used as a topical preparation, such as Neosporin (neomycin/polymyxin B/bacitracin). It can also be given orally, where it is usually combined with other antibiotics. Neomycin is not absorbed from the gastrointestinal tract and has been used as a preventive measure for hepatic encephalopathy and hypercholesterolemia. By killing bacteria in the intestinal tract, it keeps ammonia levels low and prevents hepatic encephalopathy, especially prior to GI surgery. It works as an antibiotic that is active against streptomycin-resistant bacteria, including in the case of tuberculosis organisms. It has also been used to treat small intestinal bacterial overgrowth. It is not given via injection, as neomycin is extremely nephrotoxic (causes kidney damage), even when compared to other aminoglycosides. The exception is when neomycin is included, in very small quantities, as a preservative in some vaccines – typically 25 μg per dose. Similar to other aminoglycosides, neomycin has excellent activity against Gram-negative bacteria, and is partially effective against Gram-positive bacteria. It is relatively toxic to humans, and many people have allergic reactions to it. See: Hypersensitivity. Physicians sometimes recommend using antibiotic ointments without neomycin, such as Polysporin. The following represents MIC susceptibility data for a few medically significant Gram-negative bacteria. In 2005–06, neomycin was the fifth-most-prevalent allergen in patch test results (10.0%). Neomycin, like other aminoglycosides, has been shown to be ototoxic causing tinnitus, hearing loss, and vestibular problems in a small number of patients. Patients with existing tinnitus or sensorineural hearing loss should speak with their doctor about the risks and side effects prior to taking this medication. Neomycin resistance is conferred by either one of two aminoglycoside phosphotransferase genes. A neo gene is commonly included in DNA plasmids used by molecular biologists to establish stable mammalian cell lines expressing cloned proteins in culture; many commercially available protein expression plasmids contain neo as a selectable marker. Non-transfected cells will eventually die off when the culture is treated with neomycin or similar antibiotic. Neomycin or kanamycin can be used for prokaryotes, but geneticin (G418) is, in general, needed for eukaryotes. Neomycin binds to the 30S subunit of the ribosome and inhibits translation of proteins from mRNA. Neomycin exhibits a high binding affinity for phosphatidylinositol 4,5-bisphosphate (PIP2), which is a phospholipid component of cell membranes. First isolated from the Streptomyces fradiae and Streptomyces albogriseus in 1949 (NBRC 12773). Neomycin is a mixture of neomycin B (framycetin); and its epimer neomycin C, the latter component accounting for some 5–15% of the mixture. It is a basic compound that is most active with an alkaline reaction. It is also a thermostable compound that is soluble in water while insoluble in organic solvents. Neomycin has good activity against Gram-positive and Gram-negative bacteria, but is very ototoxic. Its use is thus restricted to oral treatment of intestinal infections.