New 4-Pyridone derivatives of General Formula are claimed ##STR1## in which R.sub.1 is methylamino,4-fluorophenyl, 2,4-difluorophenyl, R.sub.2 is hydrogen or a sulfur atom that is joined to the ring nitrogen by an ethylene bride, X is a hydrogen or a physiologically removable ester group and Y is a base of the general formula ##STR2## In formula IIa and IIb, R.sub.3 is hydrogen, lower alkyl, benzyl, formyl, acetonyl or a moiety of the formula ##STR3## Also claimed are the addition salts of compounds of formula I with pharmaceutically acceptable inorganic or organic acids or base and/or their hydrates. Also claimed are the methods of manufacture of compounds of formula I and their use as antibacterial agents.