The powder form of Gentamicin for use in Cell Culture is product G1264. See the link below to access this product page:
https://www.sigmaaldrich.com/product/sigma/g1264
Additional Gentamicin product options may be reviewed at the link below:
https://www.sigmaaldrich.com/search/1405-41-0?focus=products&page=1&perpage=30&sort=relevance&term=1405-41-0&type=cas_number