TDF is another potent anti-viral treatment for chronic hepatitis B. Up to 72% and 87% of HBeAg-positive and -negative patients achieved undetectable HBV DNA by week 144 of TDF monotherapy. It is also effective in patients with prior exposure to other nucleo(s)tide analogs. Previous studies demonstrated that TDF can be used as an effective rescue therapy in lamivudine or adefovir-treated patients with incomplete virologic response.