PROBLEM TO BE SOLVED: To provide microparticles having a size sufficient to increase the half-life or survival of an active ingredient in blood, and exhibiting a low uptake in the liver and a fast cell clearance during intravenous administration.SOLUTION: The biocompatible composition includes microparticles of alginic acid or a salt thereof, and an active ingredient. More particularly, there are provided the microparticles for encapsulating the active ingredient to be intravenously administered to a patient who needs it.【課題】血中有効成分の半減期又は残存率を高めるのに十分なサイズを有するとともに、静脈内投与時に低い肝臓取込み及び迅速な細胞クリアランスを示す微粒子を提供する。【解決手段】アルギン酸又はその塩の微粒子と有効成分とを含んでなる生体適合性組成物。より詳細には、必要な患者に静脈内投与すべく有効成分を被包化するための微粒子。【選択図】図1