The synthesis of S-309309 hydrate is described in the Supplementary Material. The particle sizes of S-309309 hydrate used in this study were D50 = 2.74 µm, D90 = 8.34 µm for one sample (Lot No. B1) and D50 = 3.29 µm, D90 = 10.94 µm for the other sample (Lot No. A1); the purity (quantitative value) of these samples was 99.4% and 99.6%, respectively. D50 or D90 is defined as the size value corresponding to cumulative size distribution at 50% or 90%, which represents the size of particles below which 50%, or 90% of the sample lies. HPC, hypromellose (HPMC), and povidone (PVP), which are water-soluble polymers, were purchased from Nippon Soda Co., Ltd. (Tokyo, Japan), Shin-Etsu Chemical Co., Ltd. (Tokyo), and BASF SE (Ludwigshafen, Germany), respectively. Mannitol was purchased from Roquette Frères (Lestrem, France), lowsubstituted hydroxypropyl cellulose was purchased from Shin-Etsu Chemical Co., Ltd., magnesium stearate was purchased from SpecGx LLC (St. Louis, MO), and HPMC capsules were purchased from Lonza K.K. (Sagamihara, Kanagawa, Japan). All other chemicals and solvents were analytical reagent-grade commercial products.