Delayed Reduction of Hepatitis B Viral Load and Dynamics of Adefovir-Resistant Variants during Adefovir plus Entecavir Combination Rescue Therapy

Objective: Entecavir (ETV) added to adefovir (ADV) is recommended in the consensus for management of patients with ADV resistance. However, little attention has been focused on the delayed reduction of HBV DNA and dynamics of ADV-resistant variants during ADV-ETV combination rescue therapy in the clinical setting. We characterized the dynamics of viral load and resistant variants in nucleos(t)ide analogues (NAs)-naïve chronic hepatitis B (CHB) patients during antiviral treatment with ADV monotherapy followed by ADV-ETV combination therapy. Methods: A cohort of 55 CHB patients was enrolled in this study. Three NAs-naïve patients developed ADV-resistant variants during 24-33 months of ADV monotherapy, and then switched to ADV-ETV combination therapy. Thirty-five serial serum samples from these three patients were regularly collected during treatment. Ten mutants associated with commonly used antiviral drugs were detected by pyrosequencing. Results: HBV DNA decreased to the lowest level during ADV monotherapy at 6-18 months, with a decrease of 0.95-5.51 log(10) copies/mL, whereas rtA181V or rtN236T gradually increased with extended therapy. HBV DNA decreased to below the detectable level during ADV-ETV combination therapy at 21-24 months, with a decrease of 4.19-4.65 log(10) copies/mL. Resistant rtA181V and rtN236T were undetectable after 21-24 months of combination therapy. Moreover, no LAM-resistant rtM204I/V or ETV-resistant variants were detected during the 27-36 months of combination therapy. Conclusion: Although ADV-resistant variants were suppressed, viral load reduction was delayed during ADV-ETV combination rescue therapy in patients with ADV-resistant HBV. The quantification of resistant variants by pyrosequencing may facilitate monitoring of antiviral therapy.