The present invention addresses the problem of providing a pharmaceutical preparation composition which is a pharmaceutical preparation containing a polymerized camptothecin derivative produced by bonding a camptothecin derivative capable of associating in an aqueous solution thereof to form nano particle to a polymer carrier, and which has improved pharmaceutical stability. Particularly, the present invention addresses the problem of providing a pharmaceutical preparation capable of maintaining the nano particle-forming property thereof, which is an important factor, and having excellent storage stability. A pharmaceutical preparation which contains a block copolymer composed of a polyethylene glycol segment and a polyglutamic acid segment linked to each other, wherein the polyglutamic acid segment contains a glutamic acid unit having a camptothecin derivative bonded thereto. In an aqueous solution of the pharmaceutical preparation, associations can be formed. When the pharmaceutical preparation is prepared into an aqueous solution containing the camptothecin derivative at a concentration of 1 mg/mL, the aqueous solution has a pH value of 2.4 to 7.0. In the pharmaceutical preparation, the rate of change in the ability of forming the associations after the pharmaceutical preparation is stored at 40 DEG C for 1 week under light-blocked conditions is 50% or less.本發明之課題在於提供一種醫藥製劑組合物，其係含有使於水溶液中聚集而具有奈米粒子形成性之喜樹鹼衍生物鍵結於高分子載體上而成之高分子化喜樹鹼衍生物者，並且製劑穩定性獲得提昇。其課題尤其在於提供一種維持作為重要因子之奈米粒子形成性而保存穩定性優異之醫藥製劑。本發明之醫藥製劑係含有聚乙二醇鏈段與包含喜樹鹼衍生物所鍵結之麩胺酸單元之聚麩胺酸鏈段連結而成之嵌段共聚物者，並且上述醫藥製劑於水溶液中形成聚集體，將上述醫藥製劑製成以上述喜樹鹼衍生物含量濃度計為1mg/mL之水溶液之情形時之該水溶液之pH值為2.4~7.0，於遮光下且40℃下保存1週後，上述醫藥製劑之該聚集體之形成能力之變化率為50%以下。
