Key inclusion criteria:

• Age of 16 years and older
• Receipt of entecavir or lamivudine in a previous entecavir study.

Participants who were, based on their response to entecavir:

• Virologic nonresponders at Week 48

• Partial virologic responders who became nonresponders during the second year of treatment

• Partial virologic responders at Week 96

• Complete responders who relapsed during postdosing follow-up

  • Decompensated liver disease in AI463-048 that met 1 or more of the following criteria:

• Nonresponse to adefovir after at least 24 weeks of treatment

• Partial response to adefovir after 96 weeks of treatment

• Complete response to adefovir after relapsing during postdosing follow-up

• Demonstrated intolerance to adefovir

  • Except for those participants enrolled from AI463-048, compensated liver disease.

Key exclusion criteria:

• HIV coinfection
• Receiving nephrotoxic or hepatotoxic agents
• Ongoing opportunistic infections
• Hemoglobin level <11.0 g/dL except for those enrolled from AI463-048
• Platelet count <70,000 mm^3 except for those enrolled from AI463-048
• Absolute granulocyte count <1,500 cells/mm^3
• Recent history of pancreatitis (within 24 weeks prior to first dose of therapy)
• Current evidence of ascites requiring paracentesis, hepatic encephalopathy, or variceal bleeding, except for those enrolled from AI463-048
• Known history of allergy to nucleoside analogues.