An objective of this invention is to provide a hypodermic injection agent which is not easy to cause re-aggregation of hydroxyapatite during heat sterilization, excellent in flow properties and especially capable of been used in a small injection needle having an inner radius of 0.20mm or less, and does not cause pain and inflammation in injection.The present invention provides a hypodermic injection agent containing: a water gel containing fired hydroxyapatite particles. With respect to the total mass of the hypodermic injection agent, the content of the fired hydroxyapatite particle is 1 to 60 mass%, an average radius of the fired hydroxyapatite is 15 μ m or less, and 4% or more of the fired hydroxyapatite has an average radius of 5 μm or more and 30 μm or less.本發明提供一種皮下注射用劑,係於熱滅菌時,羥磷灰石不易產生再凝聚,流動特性優異,尤其在如內徑0.20mm以下之細注射針亦可使用,在注射時不易產生疼痛及發炎。本發明之皮下注射用劑,係具有:含燒成羥磷灰石粒子之水凝膠,以上述皮下注射用劑之全質量作為基準時,上述燒成羥磷灰石粒子之含有率為1至60質量%,上述燒成羥磷灰石粒子之平均粒徑在15μm以下,4%以上之上述燒成羥磷灰石粒子之粒徑在5μm以上30μm以下。本說明書中之圖僅為實施例中的測定結果,並非本案的代表圖。故本案無指定代表圖。
