The antibiotic G-418, also known as geneticin, is a selective antibiotic of the aminoglycoside family. G-418, produced by the bacterium Micromonospora rhodorangea, has a similar structure to gentamicin B1 and has the same mode of action on ribosomes. The classically used form of gentamicin is its disulfate.

G-418 has the particularity of inhibiting protein synthesis not only on bacteria but also on eukaryotic cells on which it has a cytotoxic effect. G-418 is said to be a selective antibiotic because it is possible to confer resistance to this antibiotic through the neo gene (neomycin resistance gene) of the Tn5 transposon. The genetically modified cells then carry the geneticin resistance gene. Selection in mammalian cells is usually achieved within 3-7 days with concentrations ranging from 400 to 1000 µg/ml.