 - Willing to prevent pregnancy - Women must agree not to become pregnant or breastfeed from the time of study enrollment until at least 3 months after the last dose of study drug. If a woman is sexually active and has no history of hysterectomy or tubal ligation, she must agree to practice an acceptable method of birth control, such as hormonal or barrier birth control. A woman is eligible if she is monogamous with a vasectomized male. Sexually active male volunteers without vasectomy must agree to use a barrier method of contraception for 3 months after the last dose of study drug. 