G418 Sulfate is recommended for use as selection agent in a concentration range of 100-800 µg/ml. This antibiotic blocks polypeptide synthesis by hindering protein elongation, and inhibits the selection and maintenance of eukaryotic cells stably transfected with the neomycin resistance gene. G418 is an aminoglycoside antibiotic similar in structure to gentamicin, neomycin and kanamycin. This antibiotic is effective against Gram-negative and some Gram positive bacteria.