Safety and Antiviral Activity Study of ACH-126,443 (Beta-L-Fd4C) in Treatment-naive Adults With Chronic Hepatitis B Virus Infection

Inclusion Criteria: * Chronic hepatitis B virus (HBV) infection, known to be hepatitis B surface antigen positive ≥ 6 months. * Plasma HBV deoxyribonucleic acid level ≥ 100,000 copies/milliliter. * Hepatitis B e-antigen positive. * Human immunodeficiency virus negative. * Basic hematologic and chemistry parameters within acceptable limits (defined in protocol). * No need for excluded medications. * Participants of reproductive capability must have utilized 2 approved forms of birth control, one of which must have been barrier protection. Exclusion Criteria: * Human immunodeficiency virus infection. * Hepatitis C co-infection. * Concurrent systemic antiviral treatment. * Previous antiviral treatment for HBV infection within 6 months prior to randomization or treatment with lamivudine for more than 6 months at any time in the past. * Previous therapy with agents with significant systemic myelosuppressive or cytotoxic potential within 3 months of study start or the expected need for such therapy at study start. * Alcohol abuse. * Pregnancy or breast-feeding. * Inability to tolerate oral medication. * Aspartate aminotransferase \> 7.0 times the upper limit of normal. * Alanine aminotransferase \> 7.0 times the upper limit of normal. * Any clinical condition or prior therapy that, in the Investigators opinion, would make the participant unsuitable for the study or unable to comply with the dosing requirements. * Use of any investigational drug.