The present invention relates to the novel quinolone carboxylic acid derivatives of the following formula (I) and their pharmaceutically acceptable salts and their hydrates. IMAGE (I) wherein X is a hydrocarbon, fluorocarbon or nitrogen atom, Y is a hydrogen or methyl group, R1 is a hydrogen or alkyl group having 1 to 5 carbon atom, R2 is IMAGE wherein A and B is a fluorocarbon or nitrogen atom, provided that, if A=CF, B=N and if A=N, B=CF) and R3 is IMAGE (wherein R4 is an amino group which makes a racemate or (S)-enantiomer) or IMAGE (wherein R5, R6 and R7 are respectively hydrogen or alkyl group having 1 to 3 carbon atom.). The compounds according to the present invention are used as antibacterial agents.
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