A novel hepatitis B virus mutation with resistance to adefovir but not to tenofovir in an HIV–hepatitis B virus-co-infected patient

A molecular virology analysis performed in an HIV-hepatitis B virus (HBV) co-infected patient showed the emergence of an unusual HBV polymerase gene mutation (rt A181T) under adefovir therapy, conferring resistance to adefovir but not to tenofovir, as proved by in-vitro phenotypic analysis. This observation suggests that careful monitoring of co-infected patients is required to diagnose HBV resistance to nucleos(t)ide analogues, and that tenofovir may be active at least against some of the adefovir-resistant strains.