Simultaneous Emergence of Entecavir Resistance Mutations in a Nucleoside-Naive Chronic Hepatitis B Patient

Background: Entecavir (ETV) has potent antiviral activity against hepatitis B virus (HBV), and the emergence of drug resistance is rare in nucleoside-naive patients. Resistance requires simultaneous appearance of three mutations which account for the very low resistance profile of ETV. We experienced one case of genotypic ETV resistance with viral rebound during ETV treatment of nucleoside-naive patients with chronic hepatitis B (CHB). Case: A 50-year-old HBV e antigen-positive man received ETV 0.5 mg/day for 120 weeks. The level of HBV DNA was 9.0 log 10 copies/ml at baseline, declined to a nadir of 2.7 at week 60 and then rebounded to 6.0 at week 108 and 7.5 at week 120. The serum alanine aminotransferase level did not increase during ETV treatment. The ETV resistance-related substitution (T184A) and lamivudine resistance-related substitutions (L180M and M204V) were detected by sequence analysis at week 96. Conclusions: The three substitutions associated with ETV and lamivudine resistance developed simultaneously without complete suppression in a nucleoside-naive CHB patient after extended therapy. In spite of the extremely rare chance of viral mutation during ETV treatment, treatment-naive patients with high pretreatment viral loads and detectable HBV DNA during treatment should be carefully monitored or undergo targeted surveillance for resistance. Copyright (C) 2012 S. Karger AG, Basel