Background/Aims
: We studied to evaluate the virological and biochemical responses to lamivudine and to detect YMDD mutants in patients who received long-term lamivudine therapy. Methods : We conducted a one-year trial of lamivudine in 45 Korean patients with chronic liver disease due to hepatitis B virus. The patients were treated with a single oral average dose of 100 mg of lamivudine every day for 12 months. Results : The suppression of serum HBV DNA was sustained in 77.8% of the patients and the normalization of serum ALT in 80%. The proportions of patients with HBeAg seroconversion were 25%. YMDD mutants were detected in 4 of 8 patients who showed sustained HBV DNA and serum ALT response (n=31) and in 3 of 8 patients who showed HBV DNA or serum ALT breakthrough (n=9). The response to lamivudine therapy in HBeAg-negative patients was excellent. Conclusion : Lamivudine therapy resulted in a significant virological and biochemical improvements and were well tolerated. But, YMDD mutants were detected during lamivudine therapy. (Korean J Hepatol 1999;5:97－104)

Background/Aims
The emergence of lamivudine-resistant mutant hepatitis B virus (HBV), with aminoacid substitution in the YMDD motif of DNA polymerase, has been reported in the long-term lamivudine use group. However there is no report about the emergence of mutant viruses during the short-term lamivudine therapy. The
objective
of this study was to investigate the emergence of YMDD mutant HBV during short-term lamivudine therapy. Methods: We evaluated twenty-eight chronic hepatitis B patients who were HBeAg and HBV DNA positive and treated with lamivudine 100mg p.o. daily for 12 weeks. First, we investigated the emergence of YMDD mutants by nested polymerase chain reaction (PCR) method developed by Chayama et al in 19 patients who lost HBV DNA during lamivudine therapy but showed HBV DNA re-emergence 2 weeks after the end of therapy. Second, DNA subcloning and sequencing of HBV DNA polymerase including YMDD motif was undertaken in one patient's serial blood samples at 0, 8, 12 weeks to confirm the results of nested PCR. Results: YMDD motif mutation was detected in 17(90%) out of 19 patients at the end of therapy and the type of mutations were YIDD only. At the end of therapy, mutant was predominant in 5 patients, both mutant and wild type were similar in proportion in 3 patients, and wild type was predominant in 9 patients. When we carried out nested PCR serially with samples of 0, 2, 4, 8, 12, 14 weeks after initiation of therapy in 5 patients who were mutant predominant at 12 weeks, YIDD mutant began to be detected from 2 weeks in 4 patients and from 4 weeks in one patient. However, rapid turnover from mutant to wild type happened after the end of therapy, so only wild type was detected in 3 patients and wild type became predominant in 2 patients at 2 weeks after the end of therapy. All the sequencing results of serial blood samples in one patient were consistent with nested PCR data. Conclusions: The presence of YMDD motif HBV polymerase mutant may be possible before administration of lamivudine in Korean chronic hepatitis B patients. Nested PCR assay would be an useful method to detect YMDD mutant. (Korean J Hepatol 1999;5:173－183)

Background/Aims
Recipients, at 13 months after administration of daily doses of 100 mg of lamivudine, were likely to have the highest rate of HBeAg seroconversion (32%); the greatest suppression of HBV DNA (98% reduction at week 52); and the highest rate of sustained normalization of ALT levels (72%). In a 1-year trial of lamivudine for chronic hepatitis B patients, the incidence of YMDD mutations was known to be about 14%. We intend to determine the incidence of YMDD mutations and the correlation between the mutation of the virus and the clinical characteristics of the patient.Methods:Between Feb. 1999 and Sept. 2000 we conducted a prospective study. Patients received 100 mg of lamivudine per day orally for at least 9 months. The average period of follow-up was 15 months. The patients enrolled in this study were composed of 20 chronic hepatitis B patients and 3 liver cirrhosis patients. The male to female ratio was 18:5. The average age of the patients was 40 years. The HBV DNA was extracted from the initial serum and the serum on abnormal ALT level, and then PCR was done. Finally we sequenced a 459-bp fragment and analyzed which samples had YMDD mutation or did not.Results:(1) The genetic mutations in the YMDD locus occurred in 3 of the 23 patients (13%), two patients exhibited YIDD mutation, and one patient exhibited YVDD at 24, 52, 48 weeks of therapy respectively. (2) During the 3 months of treatment, serum ALT levels returned to normal in 13 of the 23 patients (56%). The HBV DNA disappearance rate at 3 and 8 months was 63% and 84% respectively. The 8 of 19 patients who lost the HBV DNA during lamivudine treatment experienced the breakthrough at about 13 months (the range: 8～27 months). 4 patients experienced HBeAg seroconversion during the treatment period (17%).Conclusions:The mutations in the YMDD motif, especially the YIDD type, may aggravate the clinical outcome of the patients. We concluded that the treatment duration should be prolonged with these patients.(Korean J Hepatol 2001;7:162-170)

Background/Aims
Long-term efficacy and the rate of viral breakthrough in patients with HBeAg-negative chronic hepatitis B receiving lamivudine therapy is uncertain. This study was conducted to determine the rate of viral breakthrough according to the HBeAg status and the relation of viral breakthrough with YMDD mutants. Methods: Two hundred and five patients with HBeAg-positive and 49 patients with HBeAg-negative chronic hepatitis B, who had received lamivudine for at least 9 months, were included. The mean durations of the lamivudine treatment were 176 months and 155 months in HBeAg-positive and negative patients, respectively. Analysis of HBV genome for YMDD mutations was performed by restriction-fragment-length polymorphism assay and direct sequencing. Results: While the cumulative rates of viral breakthrough at 12th and 24th months of the lamivudine therapy were 0% and 7% in the HBeAg-negative group, they were 12% and 39% in the HBeAg-positive group. The cumulative rate of viral breakthrough in the HBeAg-negative group was significantly lower than in the HBeAg-positive group (p<0.01). In multivariate analysis, the only significant factor related to viral breakthrough was the HBeAg status (p<0.05). The YMDD mutants were detected in all patients with viral breakthrough irrespective of HBeAg status. However, in patients without viral breakthrough, the rate of YMDD mutants was significantly higher in the HBeAg-negative group than in the HBeAg-positive group (13.3% vs 5.1%; p<0.01). Conclusions: Lamivudine is expected to be more persistently effective in HBeAg-negative chronic hepatitis B because of a lower viral breakthrough rate than in HBeAg-positive chronic hepatitis B in spite of the emergence of YMDD mutants. Korean J Hepatol 2002;8:397-404)

Background/Aims
Lamivudine therapy in chronic hepatitis B has been shown to be effective in inhibiting HBV replication. However, lamivudine resistance has been developed with prolonged use. We studied to etermine the prevalence, predictive factors, and clinical outcomes of lamivudine resistance. Mutations in YMDD motif of HBV polymerase, which have been associated with lamivudine resistance, were also assessed. Methods: 170 patients with HBV-associated chronic liver disease who have received lamivudine for at least one year, were studied. The clinical, biochemical, and virologic characteristics were analyzed and compared according to presence (resistance group) or absence (non-resistance group) of DNA breakthrough. Their clinical outcomes were regularly followed. Stored sera before treatment and after DNA breakthrough were examined for detection of HBV polymerase mutation by direct sequencing and/or RFLP. Results: Cumulative rates of lamivudine resistance after one and two years of treatment were 11% and 34%, respectively. In the resistance group, as compared to the non-resistance group, age, the presence of HBeAg before treatment, and disappearance of HBeAg during treatment, were significantly different. The predictive factors associated with lamivudine resistance were not found. ALT and HBV-DNA level after lamivudine resistance was variable, but jaundice or hepatic failure was absent. Mutation in YMDD motif was detected in 73% and other variable mutations were detected before treatment and after DNA breakthrough. Conclusions: Lamivudine resistance increases the longer the duration of treatment and clinical outcomes are variable. The mutation in YMDD motif was found in about 2/3 of cases. Other causes for lamivudine resistance may be considered. (Korean J Hepatol 2002;8:405-417)