The objective of this study is to evaluate the pharmacokinetic interactions between ASP015K and metformin in healthy non-elderly male subjects.

Inclusion Criteria:

• Body weight at screening: ≥ 50.0 kg, < 80.0 kg
• BMI at screening: ≥ 17.6, < 26.4
• Subjects who agree to use highly effective contraception as consisting of two forms of birth control (at least one of which must be a barrier method) from getting informed consent through 90 days after the final study drug administration.
• Subjects who agree NOT to donate sperm from getting informed consent through 90 days after the final study drug administration.

Exclusion Criteria:

• Subjects who received or are scheduled to receive any investigational drugs in other clinical trials or post-marketing studies within 120 days before screening test or during the screening test to the hospital admission (Day -1).
• Subjects who received or is scheduled to receive any medications (including over-the-counter drugs) within seven days before the hospital admission (Day -1).
• Subjects who received ASP015K or metformin previously.
• Subjects who have a habit of excessive alcohol drinking or smoking.
• Any deviation from the normal range of blood pressure, pulse, body temperature, or 12-lead ECG at screening or on the day of hospital admission (Day -1).
• Subjects who meet any of the following criterion for laboratory tests at screening or on the day of hospital admission (Day -1). Normal ranges of each test specified at the study site or test/assay organization will be used as the normal ranges in this study.
• Subjects with a complication or history of drug allergies.
• Subjects who have a history of clinically serious allergy, which induces generalized urticaria or anaphylactic shock requiring hospital admission.
• Subjects with a complication or history of hepatic disease, renal disease, cardiac disease, congenital short QT syndrome, respiratory disease , gastrointestinal disease.
• Subjects with a history of gastrointestinal resection.
• Subjects who developed upper gastrointestinal symptoms within seven days before the hospital admission (Day -1).
• Subjects with a complication or history of endocrine disease, cerebrovascular disease, malignant tumor, lymphatic disease , lactic acidosis.
• Subjects who apply to any of the concerns with regard to tuberculosis.
• Subjects who apply to any of the concerns with regard to infection other than tuberculosis.
• Subjects with vaccination of live vaccines or live attenuated vaccines within 56 days before the hospital admission (Day -1).

Access to anonymized individual participant level data will not be provided for this trial. Further details on Astellas' data sharing policy can be found at https://www.clinicaltrials.astellas.com/transparency/.