 - Because nucleoside analogs are known to be teratogenic, women of child-bearing potential and men must agree to use two forms of contraception hormonal or barrier method of birth control; abstinence; sterilization prior to study entry, for the duration of study participation, and for 3 months after completing study treatment. Should a woman become pregnant or suspect she is pregnant while she or her partner is participating in this study, she should inform her treating physician immediately. Men treated or enrolled on this protocol must also agree to use two forms of contraception prior to the study, for the duration of study participation, and for 3 months after completion of administration of TdCyd. 