PROBLEM TO BE SOLVED: To provide a prodrug of pyridone carboxylic acid antibacterial drug with which hydrolysis occurs quickly after gastrointestinal absorption so that a pyridone carboxylic acid antibacterial drug of an active pharmaceutical ingredient is regenerated, and which is hard to cause pseudomembranous colitis.SOLUTION: The invention relates to an ester prodrug represented by the formula (I), which is alkoxy carbonyl hemiacetal type ester of a pyridone carboxylic acid antibacterial drug for inhibiting adverse reactions of intestinal bacterial replacement and/or using in combination with a polyvalent metal-containing medicine. [In the formula, Z1-Z3 are a substituted/unsubstituted hydrocarbon group, a nitrogen-containing hydrocarbon group, or an oxygen-containing hydrocarbon group； adjacent two may form together a ring； R6 is H or alkyl of C1-6； and R7 is alkyl of C1-6.]【課題】腸管吸収後、速やかに加水分解されて原薬のピリドンカルボン酸系抗菌薬が再生され、偽膜性大腸炎を起こし難いピリドンカルボン酸系抗菌薬プロドラッグの提供。【解決手段】式（Ｉ）で表される、腸内菌交代副作用抑制用の、及び／又は、多価金属含有医薬併用用のピリドンカルボン酸系抗菌薬のアルコキシカルボニルヘミアセタール型エステルである、エステルプロドラッグ。［Ｚ1～Ｚ3は置換／未置換の炭化水素基、含窒素炭化水素基又は含酸素炭化水素基；隣接する二つは一緒になって環を構成してもよい；Ｒ6はＨ又はＣ１～６のアルキル；Ｒ7はＣ１～６のアルキル］【選択図】図１
