 GSK2881078 is a selective androgen receptor modulator SARM that is being evaluated for effects on muscle growth and strength in subjects with muscle wasting to improve their physical function. Part A of this study will evaluate the safety, efficacy and pharmacokinetics of GSK2881078 in healthy, older men and post-menopausal women who will take daily dosing for 28 days and be followed for a total of 70 days. Part B of this study will characterize the effect of Cytochrome P450 3A4 CYP3A4 inhibition on the GSK2881078 pharmacokinetics. Part B will only be conducted if safe and efficacious dose is identified in Part A. Part A will include healthy older males and post-menopausal females; and randomize approximately 60 subjects about 15 per cohort 4 cohorts to complete approximately 48 about 12 per cohort. Part B will enroll one cohort of approximately 15 healthy male subjects to complete approximately 12. The study duration will be approximately 115 days for Part A and 122 days for Part B. 