15. Female study volunteers of reproductive potential must have a negative serum or urine pregnancy test on the day of enrollment into the study. All female study participants are presumed to be of reproductive potential unless they have been post-menopausal for at least 24 consecutive months or have undergone surgical sterilization (e.g. hysterectomy, bilateral oophorectomy, or salpingotomy). If participating in sexual activity that could lead to pregnancy, the female study volunteer must use a form of contraception listed below starting at least 21 days prior to enrollment and continuing to Week 48 of the study. At least one of the following methods MUST be used appropriately (with or without hormone-based method):