 Since TDF and adefovir ADV, another licensed drug for CHB, belong to same molecular group, acyclic phosphonate, there had been various studies investigating the efficacy of TDF in ADV-resistant patients. The efficacy of tenofovir in this group of patients is conflicting. While several studies have shown TDF achieving similar viral suppression when compared to CHB patients without ADV-resistance , another study found that patients with the signature ADV mutations of rtA181VT and or rtN236T responded suboptimally to TDF. For all published studies, the number of patients with documented genotypic resistance to adefovir is actually small n 17-40, and therefore, further studies in this area are required. 