• Compare rate of complete response (CR) as measured by complete virologic and biochemical response at 24 and 48 weeks in patients who had been treated with adefovir for 24 and 48 weeks prior to switching. [ Time Frame: 48 weeks or after ] [ Designated as safety issue: No ]
• Compare rates of biochemical response (BR) as measured by ALT normalization on the 2 different treatments at corresponding treatment milestones as above. [ Time Frame: 48 weeks or after ] [ Designated as safety issue: No ]

We propose a largely retrospective study with short-term prospective follow-up in a subgroup of patients who have not yet been treated with 48 weeks of entecavir following partial response to adefovir. The aim of the study is to describe sequential virologic response to adefovir and entecavir.

• Persistent viremia after 48 weeks or longer.
• <2 log IU/mL drop from initial HBVDNA after 12 weeks of adefovir

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Inclusion Criteria:

• Age 18 years or older
• All genders and ethnicity
• Positive HBsAg
• HBeAg positive and negative
• Pretreatment HBV DNA of 10,000 copies/mL or higher (for purposes of this study, both copies and equivalent IU measurements will be recorded and analyzed)
• Patients who are switched to entecavir after treatment with adefovir for at least 12 weeks by the providing physician.
• Less than a 2 log drop in HBV DNA from baseline at week 12.
• Patient already on adefovir for 24 weeks and still have > or equal to 1000 copies/mL of HBV DNA.
• Patients who still have positive HBV DNA PCR after 48 weeks or longer of adefovir.

Exclusion Criteria:

• Patients who refused to consent to the study
• Patients younger than 18
• Vulnerable subjects such as pregnant women, prisoners, employees, patients with significant cognitive deficits.
• Patients with prior exposure to another nucleoside for more than 2 weeks.
• HIV co-infection
• HCV co-infection
• HDV co-infection
• Recipients of solid organ transplantation
• Patients who receive high-dose steroid (60 mg/d or higher and for longer than 10 days)