 - Females must be post-menopausal, surgically incapable of bearing children, or practicing a reliable single barrier method of birth control condom, intrauterine devices, spermicide and barrier, Depot. Partnerspouse sterility may also qualify at the investigators discretion. Females of child-bearing potential must have a negative urine pregnancy test at baseline. Oral contraceptives are not acceptable as there is a potential interaction with AST-120. 