Disclosed is an sustained release preparation which releases a poorly soluble medicinal agent in a pH-independent manner. Also disclosed is an sustained release preparation which is capable of controlling the Cmax of a medicinal agent to an adequate amount and is thus capable of maintaining the level of the medicinal agent in the blood to a level at which medicinal effects can be expected for a long period of time. Specifically disclosed is an sustained release preparation which is characterized by containing a pharmaceutically acceptable salt of 4-bromo-6-[3-(4-chlorophenyl)propoxy]-5-(3- pyridylmethylamino)-3(2H)-pyridazinone, and hypromellose. An organic acid is blended in the sustained release preparation in an amount of less than 1% by mass.本發明之課題係以提供難溶性藥劑具非依賴pH之溶出性的緩釋性製劑為目的。進而本發明係以提供將藥劑之Cmax調節至適切量，且經長時間血液中的藥劑濃度可維持於預期藥效程度之緩釋性製劑為目的。本發明之解決方式係提供一種緩釋性製劑，其特徵係含有4-溴-6-[3-(4-氯苯基)丙氧基]-5-(3-吡啶基甲基胺基)-3(2H)-噠嗪酮之藥學上許可之鹽，以及羥丙甲纖維素，且有機酸之混合量未達1質量%。
