Objective: Hepatitis B infection is not actually a curable disease, and the goal is only repression of viral replication and therefore often requires lifelong treatment. Long-term antiviral therapy leads to the emergence of resistant mutant viruses. Mutations in the reverse transcriptase gene region, which is the main target region of the nuleos(t)ide analogues, is the biggest problem in the treatment. The aim of this study was to evaluate the nucleos(t)ide resistance mutations in patients with chronic hepatitis B (CHB) treatment failure.

Method: In this study; the results of HBV drug resistance of 120 patients with CHB who were followed-up in various clinics of Inonu University Medical Faculty between 2006-2018 were evaluated retrospectively. In determining the drug resistance; commercial reverse hybridizationbased tests and pyrosequencing method were used.

Results: Approximately 52% of single and 48% of multiple base mutations were detected in 120 patients included in the study. In addition to various primary mutations leading to adefovir resistance such as rtA181T/V and rtN236T, compensatory mutations such as rtL180M, rtL80V/I and rtV173L have also been found most of which are responsible for lamivudine/telbivudine resistance. rtM204V/I (34.16%) was the most common among single base mutations and rtM204V/I+rtL180M (18.33%) was the most common among multiple base mutations.

Results: HBV resistance mutations should be monitored long-term and permanently. Especially in cases such as treatment failures suggestive of the presence of resistance, more extensive mutation analysis should be performed and treatment regimens should be continuously updated depending on the presence of these mutations.