Low efficacy of entecavir therapy in adefovir‐refractory hepatitis B patients with prior lamivudine resistance

Summary. We determined the virologic response, incidence of entecavir resistance, and evolution of lamivudine and adefovir‐resistant mutants during entecavir (ETV) therapy in adefovir‐refractory patients with prior lamivudine resistance. Forty adefovir‐refractory chronic hepatitis B patients with prior lamivudine resistance who had received entecavir for ≥6 months were included and monitored for virologic response and entecavir resistance. Ten per cent of patients achieved HBV DNA < 50 copies/mL by PCR after 24 weeks of ETV therapy, and an initial virologic response was observed in 12 of 40 patients (30%). Higher pretreatment ALT (P = 0.039) and the presence of the rtL180M mutation (P = 0.038) were associated with an initial virologic response. During a mean follow‐up of 11.4 months, four patients (10%) experienced virologic breakthrough, while ETV‐resistant mutants were detected in six patients (15%). YMDD and adefovir‐resistant mutants were detected in 57 and 35% of patients at baseline, respectively. At 48 weeks of therapy, 96 and 4% of patients had YMDD and adefovir‐resistant mutants, respectively. These data suggest an early development of ETV resistance and low antiviral response during ETV therapy in adefovir‐refractory patients with prior lamivudine resistance.