ABSTRACT
<p><b>OBJECTIVE</b>To investigate the resistance mutation patterns of hepatitis B virus(HBV) during adefovir dipivoxil (ADV) monotherapy or combination therapy after lamivudine(LAM) resistance.</p><p><b>METHODS</b>Serum samples from fifteen patients with suboptimal viral response to ADV therapy after LAM resistance were collected. The RT region of HBV P gene was PCR-applied, cloned and sequenced, and the mutation patterns in relation to resistance were analyzed.</p><p><b>RESULTS</b>The ADV resistance mutation patterns of A181T+N236T, A181V, A181T were selected in ADV monotherapy group. The LAM resistance mutation patterns of M204V+L180M, M204V+L180M+L229V, M204I+L80I, M204V+L180M+V207I were detected in the combination therapy group. 20% of clones from three serum samples were detected double resistance to LAM and entecavir (ETV) in the combination therapy group, the resistance patterns were M204I+L80I+T184I (2/10), M204V+L180M+T184S (2/10), and M204V+L180M+G173L+S202G (2/10) respectively. I269L clones were detected in two serum samples from both two groups and P109S clones also detected in the one from monotherapy group.</p><p><b>CONCLUSIONS</b>In the patients with suboptimal viral response to ADV therapy after LAM resistance, the ADV resistance mutation patterns of A181T+N236T, A181V and A181T could easily be selected during ADV monotherapy; while in the patients with combination therapy, the LAM resistance mutation patterns of M204V+L180M, M204V+L180M+L229V, M204I+L80I, and M204V+L180M+V207I were predominant, the ETV resistance mutation T184I/S and S202G could be selected. The mutation patterns of I269L and P109S may impact the responses to ADV therapy in some patients.</p>