A novel pyridinecarboxylic acid derivative or its salt which has excellent effects against bacteria such as methicillin resistant Staphylococcus aureus, Pseudomonas aeruginosa, Clostridium difisil, and is not susceptible to drug efflux pumps and contains it Antibacterial agent.Formula (1): R1 in formula (1), R1 is hydrogen atom, halogen atom, lower alkyl group, amino group R2 is base nh-r6 (where R6 is hydrogen atom, lower alkyl group, amino low alkyl group, etc.), base o-r7 (where R7 is hydrogen atom, low) Class alkyl (+ alkyl), group - (CH2) m-r8 (where R8 is an amino group other, M is 1 to 4 integers) or the following equation (2): (y) y or C - R9 ar9b (where r9a and r9b are independently hydrogen atoms, low)The cyclic amino group represented by the alkyl group, the amino group, the lower alkyl amino group, etc., N and P is an integer of 1 or 2 R3 is hydrogen atom, halogen atom, lower alkyl group R4 is a hydrogen atom or carboxyl group protecting group R5 is hydrogen A pyridone carboxylic acid derivative or salt thereof represented by a child or hydroxy group.メチシリン耐性黄色ブドウ球菌や緑膿菌、クロストリジウム・ディフィシル等の細菌に対しても優れた効果を有し、かつ薬剤排出ポンプの影響を受けにくい新規なピリドンカルボン酸誘導体又はその塩及びこれを含有する抗菌剤の提供。下記式(1):〔式中、R1は水素原子、ハロゲン原子、低級アルキル基、アミノ基;R2は基-NH-R6(ここで、R6は水素原子、低級アルキル基、アミノ低級アルキル基他)、基-O-R7(ここで、R7は水素原子、低級アルキル基他)、基-(CH2)m-R8(ここで、R8はアミノ基他、mは1~4の整数)又は次式(2):(式中、YはNH又はC-R9aR9b(ここで、R9a及びR9bはそれぞれ独立して水素原子、低級アルキル基、アミノ基、低級アルキルアミノ基他、)、n及びpは1又は2の整数)で表される環状アミノ基;R3は水素原子、ハロゲン原子、低級アルキル基他;R4は水素原子又はカルボキシル基保護基;R5は水素原子又は水酸基保護基〕で表されるピリドンカルボン酸誘導体又はその塩。
