Currently, five nucleos(t)ide analogs are approved for the treatment of chronic hepatitis B, namely lamivudine, adefovir dipivoxil, telbivudine, entecavir (ETV) and tenofovir disoproxil fumarate (TDF). ETV and TDF are recommended as first-line therapy by all regional guidelines due to their high anti-viral potency and low risk of inducing resistance.