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In a recent phase II clinical study, 13 chronic hepatitis B-infected patients treated daily with 30 mg adefovir dipivoxil for 12 weeks displayed a median 4.1-log10 decrease in plasma hepatitis B virus (HBV)-DNA levels. The decline of viral load during therapy displayed a biphasic kinetic profile that was modeled to determine the efficacy of inhibition of viral production, as well as kinetic constants for the clearance of free virus and the loss of infected cells. Viral production was suppressed with an efficacy of 0.993 +/- 0.008, indicating that only 0.7% of viral production persisted during therapy. The initial, faster phase of viral load decline reflects the clearance of HBV particles from plasma with a half-life of 1.1 +/- 0.3 days, translating to a 48% daily turnover of the free virus. The second, slower phase of viral load decline closely mirrors the rate-limiting process of infected cell loss, with a half-life of 18 +/- 7 days. The duration of therapy required to completely eliminate the virus from plasma or suppress it to levels sufficient to induce seroconversion is a function of the half-life of the free virus, the half-life of infected cells, and the efficacy of inhibition of virus production from infected cells. These quantitative analyses provide a more detailed picture of the dynamics of HBV infection and therapy, and can be used to compare the efficacy of various doses and inhibitors of HBV replication for the treatment of HBV infections.

To determine whether adefovir is active against lamivudine-resistant hepatitis B virus (HBV), the inhibition constants of adefovir diphosphate and lamivudine triphosphate for wild-type and mutant human HBV DNA polymerases, which contain amino acid substitutions associated with lamivudine resistance, were compared. Recombinant wild-type and mutant human HBV DNA polymerases were expressed and substantially purified using a baculovirus expression system and immunoaffinity chromatography. HBV DNA polymerase mutants M552I, M552V, and L528M/M552V showed resistance to lamivudine triphosphate with inhibition constants (Ki) increased by 8.0-fold, 19.6-fold, and 25.2-fold compared with that of wild-type HBV DNA polymerase. However, these mutants remained sensitive to adefovir diphosphate with the inhibition constants increasing by 1.3-fold and 2.2-fold or decreasing by 0.79-fold. The L528M single mutation, identified in patients with increasing HBV DNA levels during therapy with famciclovir, also remained sensitive to adefovir diphosphate with the inhibition constant increased by only 2.3-fold.