We tried to develop S-309309 formulation by simple manufacturing methods with the goals of achieving rapid dissolution of S-309309 in the small intestine and suppression of compound 8 formation in the stomach. The results suggested that the mixing S-309309 with a water-soluble polymer improved the wettability of S-309309, thereby increasing its dissolved concentration and dissolution rate. We also found that encapsulating S-309309 should suppress the increase of compound 8 amount in the stomach. These findings provide useful information for designing and developing a S-309309 formulation that is both safe and efficacious.