G-418 (disulfate) is an aminoglycoside antibiotic similar in structure to gentamicin B1, which blocks polypeptide synthesis by inhibiting the elongation step in both prokaryotic and eukaryotic cells. In Vitro: G418 is an inhibitor of many pro- and eukaryotes at concentrations from 1-300 microgram/mL. Resistance to G418 conferring by the neo gene from Tn5 encoding an aminoglycoside 3'-phosphotransferase, APT 3' II is commonly used in laboratory research to select genetically engineered cells^[1]. In general for bacteria and algae concentrations of 5 mg/L or less are used, for mammalian cells concentrations of approximately 400 mg/L are used for selection and 200 mg/L for maintenance. Resistant clones selection could require from 1 to up to 3 weeks^[2]. In Vivo: G418 (40 and 80 mg/kg) for three consecutive days are sufficient to eliminate all nontransfected T. brucei brucei parasites from infected mice^[3].