Chronic hepatitis B: preventing, detecting, and managing viral resistance.

Licensed oral agents for antiviral therapy in patients with chronic hepatitis B virus (HBV) infection include lamivudine, adefovir, entecavir, and telbivudine. Emtricitabine, tenofovir, and the combination of tenofovir plus emtricitabine in 1 tablet, which are licensed for the treatment of human immunodeficiency virus infection, are additional off-label options for treating HBV infection. Preventing HBV antiviral drug resistance to nucleoside/nucleotide analogues and appropriate management when resistance occurs has become a major focus in the management of chronic hepatitis B. HBV antiviral drug resistance may be best prevented by using an agent or combination of agents with a high genetic barrier to resistance, and 2 potent nucleoside and nucleotide drugs with different resistance profiles may prove to be the optimal first-line treatment for chronic hepatitis B. Frequent assessment of quantitative serum HBV DNA remains the best approach to early detection of resistance, and antiviral therapy should be modified as soon as resistance is detected. Results from several clinical trials have shown that the addition or substitution of newer antiviral agents can restore suppression of viral replication, normalize alanine aminotransferase levels, and reverse histologic progression in patients with resistance to lamivudine, but little information exists regarding the long-term benefits of second-line treatment regimens. Despite the substantial advances in treatment made to date, new agents with novel viral targets will be needed for patients who ultimately may fail second- or third-line therapy.