Dynamics of lamivudine-resistant hepatitis B virus strains in patients with entecavir rescue therapy.

Entecavir rescue therapy is frequently used in patients with lamivudine-resistant hepatitis B virus (HBV) strains. The aim of this study was to investigate evolutionary patterns of HBV quasispecies during entecavir rescue therapy and evaluate their impacts on therapeutic efficacy. We enrolled 21 chronic hepatitis B patients who failed to respond to lamivudine therapy and were switched to entecavir treatment. Measurement of serum HBV DNA and sequence analysis of HBV reverse transcriptase were done up to 144 weeks. Four patients of this series showed a reversion to wild-type HBV after entecavir treatment and in three of them, a complete viral response (<2.6 log10 copies/ml) was achieved. An additional five patients developed entecavir genotypic resistance, with prior occurrence of lamivudine-resistant mutation (L180 M ± M204 V/I). A viral breakthrough was observed in four of the five patients with entecavir-resistant mutants. The remaining 12 patients of this series showed dominance of lamivudine-resistant mutants throughout the entecavir rescue therapy, and five of them achieved a complete viral response at the end of follow-up. The average HBV DNA level was significantly lower in patients with a reversion to wild-type HBV than in those without it (P < 0.05). In conclusion, reversion to wild-type HBV is a favorable indicator for response to entecavir rescue therapy in lamivudine-refractory patients with chronic hepatitis B. The presence of lamivudine-resistant mutations contributes to the development of entecavir resistance.