Background/Aims: Lamivudine is an effective therapy in chronic hepatitis B patients, but the emergence of resistant hepatitis B virus (HBV) mutants is a major concern. This study was performed to investigate whether serum viral DNA levels during lamivudine therapy are related with viral breakthrough in patients with chronic HBV infection. Methods: This study consisting of 103 patients was performed retrospectively and prospectively. Follow-up duration was 24 months after lamivudine therapy. Serum HBV DNA levels were quantified by PCR-based assay every 6 months. Results: Cumulative rate of viral breakthrough was 0%, 19.4%, 36%, and 48.5% in 6, 12, 18, and 24 months respectively. The rate of viral breakthrough in 24 months increased as serum HBV DNA levels increased at 6 months. When serum HBV DNA levels were 2-3 log10, 3-4 log10, 4-5 log10, and 5 log10 copies/mL or more, the breakthrough rates were significantly higher than that of the HBV DNA level less than 2 log10 copies/mL. The relative risks were 1.10, 1.93, 2.69, 3.21 respectively (P<0.001). The viral breakthrough rate also increased as serum HBV DNA levels at 12 months increased. When the HBV DNA levels were 2-3 log10, 3-4 log10, 4-5 log10, and 5 log10 copies/ mL or more, the breakthrough rate were significantly higher than those of HBV DNA level less than 2 log10 copies/mL. The relative risks were 2.42, 4.35, 3.73, 2.61, respectively (P=0.002). Conclusions: The serum HBV DNA levels at 6 months and 12 months during lamivudine therapy can be closely correlated with the rate of viral breakthrough in 24 months. (Korean J Hepatol 2006;12:173-183)
