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.

Hepatitis B virus (HBV) infection has been a major global cause of morbidity and mortality. The recognition of the problem led to a worldwide effort to reduce transmission of HBV through routine infant vaccination. HBV infection is the most common cause of chronic liver diseases and hepatocellular carcinoma in Korea. After hepatitis B vaccine era, seroprevalence of hepatits B surface antigen is decreasing, particularly in children. Hepatitis B vaccine is remarkably safe and shows high immunogenicity. Universal childhood immunization with three doses of hepatitis B vaccine in the first year of life is a highly effective method for prevention and control of hepatitis B.

Clevudine (CLV) is a nucleoside analog with potent antiviral activity against chronic hepatitis B virus (HBV)infection. Viral resistance to CLV in patients receiving CLV therapy has not been reported. The aim of this study was to characterize CLV-resistant HBV in patients with viral breakthrough (BT) during long-term CLV therapy. The gene encoding HBV reverse transcriptase (RT) was analyzed from chronic hepatitis B patients with viral BT during CLV therapy. Sera collected from the patients at baseline and at the time of viral BT were studied. To characterize the mutations of HBV isolated from the patients, we subjected the HBV mutants to in vitro drug susceptibility assays. Several conserved mutations were identified in the RT domain during viral BT, with M204I being the most common. In vitro phenotypic analysis showed that the mutation M204I was predominantly associated with CLV resistance, whereas L229V was a compensatory mutation for the impaired replication of the M204I mutant. A quadruple mutant (L129M, V173L, M204I, and H337N) was identified that conferred greater replicative ability and strong resistance to both CLV and lamivudine. All of the CLV-resistant clones were lamivudine resistant. They were susceptible to adefovir, entecavir, and tenofovir, except for one mutant clone. In conclusion, the mutation M204I in HBV RT plays a major role in CLV resistance and leads to viral BT during long-term CLV treatment. Several conserved mutations may have a compensatory role in replication. Drug susceptibility assays reveal that adefovir and tenofovir are the most effective compounds against CLV-resistant mutants. These data may provide additional therapeutic options for CLV-resistant patients.Chronic hepatitis B virus (HBV) infection is a major health problem worldwide and leads to chronic hepatitis, cirrhosis, and hepatocellular carcinoma (13). Antiviral treatment for chronic hepatitis B improves the outcome of the disease and prevents the development of hepatocellular carcinoma (14). Currently, several oral antiviral agents, including lamivudine (LMV), adefovir (ADV), and entecavir (ETV), have been approved for the treatment of chronic HBV infections (8). However, oral antiviral treatment does not provide a cure or durable remission and it has limited long-term efficacy due to the emergence of resistance (12). Long-term treatment with nucleos(t)ide analogs is associated with an increased risk of drug resistance. Antiviral drug resistance in patients infected with HBV is associated with subsequent virologic breakthrough (BT), viral rebound, and biochemical BT.Clevudine [1-(2-deoxy-2-fluoro-␤-arabinofuranosyl)thymine, L-FMAU] (CLV) is a pyrimidine analog with potent antiviral activity against HBV (4). CLV inhibits the DNA-dependent DNA activity of HBV polymerase, as well as reverse transcription and priming (1, 16). Phase III clinical trial results have shown that CLV therapy for 24 weeks has a potent and sustained antiviral effect in both HBeAg-positive and -negative chronic hepatitis B patients (23,24). Clinica...

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The presence of single genotype and unique mutations may be related with the circulation of endemic HAV over a long period of time in Korea.