Safety and Efficacy of Adefovir Dipivoxil in Children and Adolescents With Chronic Hepatitis B

The purpose of this study is to investigate the efficacy and safety of adefovir dipivoxil for the treatment of chronic hepatitis B in children and adolescents (age 2 to less than 18 years) following 48 weeks of placebo-controlled, double-blind treatment and following an additional 192 weeks of open-label adefovir dipivoxil treatment.

Weeks 1 through 48 (Study Year 1): The first 48 weeks of the study were a randomized, double-blind, placebo-controlled, parallel-group treatment period. Participants were randomly assigned to treatment in a 2:1 fashion to ADV or PLB. Prior to randomization, eligible participants were classified into 1 of 6 strata based upon age at screening (2 to \< 7 years; \>= 7 to \< 12 years; \>= 12 to \< 18 years) and prior exposure to treatment for chronic hepatitis B (CHB) (prior treatment; no prior treatment).

Weeks 49 through 240 (Study Years 2 through 5): At Week 48, all placebo-treated participants who did not exhibit HBeAg or hepatitis B surface antigen (HBsAg) seroconversion at Week 44, plus all ADV-treated participants, were offered the opportunity to receive open-label ADV for up to an additional 192 weeks. Any participant with HBV DNA \>= 1000 copies/mL at 2 consecutive visits 12 weeks apart was to be discontinued from open-label study treatment. The only exception was for participants in the adolescent age range with prior lamivudine experience who were allowed the opportunity to add lamivudine to ADV; similarly, if combination failed to impart suppression of HBV DNA below 1000 copies/mL (confirmed) discontinuation was necessary. All participants who discontinued study drug due to confirmed seroconversion were requested to continue to return for study visits for the remainder of the study in order to evaluate the durability of seroconversion. Participants who wished to discontinue study treatment and withdraw from the study prior to study completion were requested to return every 4 weeks for 16 weeks for posttreatment evaluations following an early termination visit. Any participants who experienced posttreatment hepatic flares during the 16-week follow-up period were to be followed every 4 weeks until their ALT levels returned to \<= 2 times the upper limit of normal (ULN) for a maximum off-treatment follow-up of 6 months. Participants who experienced a severe hepatic flare (per protocol definition) after discontinuation of ADV during the open-label treatment period may have been eligible to receive ADV for treatment of the hepatic flare (after consultation with the Gilead medical monitor).

Eligibility Criteria:
Key Inclusion Criteria:

* Positive HBsAg \>= 6 months prior to randomization and positive HBeAg at screening.
* Serum HBV DNA greater than or equal to 1 x 100,000 copies/mL (PCR assay) at initial or confirmatory screening visit.
* Serum ALT levels greater than or equal to 1.5 x ULN at both initial and confirmatory screening visits.
* Compensated liver disease with anticipated survival greater than 12 months and with the following laboratory and clinical parameters within 4 weeks of baseline: \*Prothrombin time less than or equal to 1 second above normal range. \*Total bilirubin less than 1.3 mg/dL or normal direct bilirubin. \*Serum albumin greater than 3 g/dL (greater than 30 g/L). \*No clinical history of ascites, variceal bleeding, encephalopathy or splenomegaly. \*Adequate renal function defined as creatinine clearance greater than or equal to 80 mL/min (calculated using Schwartz Formula).

Key Exclusion Criteria:

* Received immunoglobulin, interferon or lamivudine therapy within 6 months prior to initial screening visit.
* Participated in any investigational trial with any investigational compound within 2 months prior to initial screening.
* Organ or bone marrow transplant recipients.
* Clinical evidence of decompensated liver disease.
* A Child-Pugh-Turcotte score greater than 6.
* Inability to comply with study requirements.