Background: Adefovir dipivoxil (ADV) is a potent nucleotide analogue against both the wild-type and lamivudine (LMV) resistant hepatitis B virus (HBV). The cumulative incidence of ADV resistant mutations in the nucleoside/-tide treatment naïve chronic hepatitis B patient (CHB) at weeks 48, 96, and 144 was 0, 0.8-3%, and ∼5.9%, respectively. Aims: The aim of this study was to characterise the genotypic and phenotypic mutation profiles to ADV in 67 LMV resistant CHB patients who were treated with ADV. Methods: Serum HBV DNA was quantified by real time polymerase chain reaction. The ADV mutant was detected using matrix assisted laser desorption/ionisation time of flight mass spectrometry based genotyping assays, termed restriction fragment mass polymorphism (RFMP). Results: RFMP analysis revealed that a total of 11 amino acid substitutions developed in the rt domain of the HBV polymerase in nine patients. The cumulative incidence of genotypic ADV resistance at months 12 and 24 was 6.4% and 25.4%, respectively. The rtA181V, rtN236T, and rtA181T mutations were detected in five, four, and two of the 67 patients at treatment months 12-17, 3-19, and 7-20, respectively. Serial quantification of serum HBV DNA revealed that two patients with the rtA181V mutation, with or without the rtN236T mutation, and one patient with the rtA181T mutation displayed HBV DNA rebound. Conclusion: Emergence of the ADV mutation in LMV resistant patients who are treated with ADV appeared to present earlier and more frequently than was reported in previous studies on nucleoside/-tide treatment naïve patients.
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