6. If female and of childbearing potential, the subject must have a negative β-hCG test at screening and a negative urine human chorionic gonadotropin (HCG) test at check-in and be willing and able to use one of the following medically acceptable double barrier methods of birth control from the screening visit through the end-of-study visit: non-hormonal intrauterine device with condom, diaphragm with condom, or condom with spermicide. Female subjects who are postmenopausal (1 year since last menses) must have elevated follicle stimulating hormone (FSH) level above 35 U/L, or be surgically sterile.