tivity at the time of screening.  Ongoing treatment with one or more NUCs for at least 000 weeks before study entry. Subjects may have a brief interruption of treatment for medical reasons (e.g. breast feeding) not to exceed 0 weeks and none within the 00 weeks before study entry.  ALT level less than or equal to 0 ULN based on at least two determinations taken at least one month apart during the 00 weeks before study entry with the second being at time of screening  Written informed consent  