Provided is a novel oral preparation (specifically, an intraoral quickly-disintegrating preparation) that allows a bitter-tasting drug such as silodosin, which has a very strong bitter taste, to be taken without an uncomfortable feeling and even without water, and that has solubility sufficient for reproducing a blood concentration effective for treating dysuria accompanying benign prostatic hyperplasia. The present invention pertains to masking particles and a novel oral preparation containing said masking particles. The masking particles are obtained by granulating or coating drug particles containing a bitter-tasting drug (e.g. silodosin) with a coating agent containing a methyl methacrylate-diethylaminoethyl methacrylate copolymer, wherein the content of said copolymer is 80-400 parts by mass relative to 100 parts by mass of the bitter-tasting drug (e.g. silodosin).本發明所提供的新穎經口投與製劑(特別係口腔內速崩解製劑)，係具苦味藥劑(例如極強烈苦味藥劑的西羅多辛)，能沒有異物感，即便未搭配水仍可服用，且具備有在因前列腺肥大症所伴隨之泌尿障礙等治療時可重現有效血中濃度之溶出性。本發明相關的遮蔽粒子及含有該遮蔽粒子的新穎經口投與製劑等，係將含有具苦味藥劑(例如西羅多辛)的藥物粒子，利用含有甲基丙烯酸甲酯-甲基丙烯酸二乙胺基乙酯共聚合體的包覆劑，施行造粒或被覆而獲得的遮蔽粒子；其中，該共聚合體含量相對於具苦味藥劑(例如西羅多辛)100質量份係80質量份~400質量份。
