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Summary and conclusion 235<br />

The inference is performed in the Bayesian framework using the Markov chain Monte<br />

Carlo methodology. The methodology is applied to data from the Dutch primary biliary<br />

cirrhosis study.<br />

STATISTICAL MODELS OF EARLY TREATMENT<br />

EFFECTS<br />

Viral dynamics during and after entecavir therapy in patients with chronic hepatitis B are<br />

described in Chapter 4.1.<br />

Nucleoside analogues inhibit HBV replication. Entecavir, a guanine nucleoside, has also<br />

been shown to reduce covalently closed circular DNA (cccDNA) to undetectable levels<br />

in wood chucks chronically infected with hepatitis virus.<br />

Mathematical description of changes in viral load during and after therapy may help to<br />

understand the process that takes place during nucleoside analogue treatment.<br />

Ten chronic hepatitis B patients were evaluated with a mathematical model during<br />

treatment with and after withdrawal of four doses of entecavir. Blood was drawn for<br />

HBV DNA measurement at frequent intervals. Decay and rebound of viral concentration<br />

during and after entecavir therapy, respectively, showed a bi phasic pattern. Non-linear<br />

modelling was used to fit individual patient data.<br />

The median effectiveness in blocking viral production was 96% and the median half-life<br />

of viral turn-over was 16 h. The median half-life of infected hepatocytes was 257 h. Data<br />

on levels of cccDNA in the liver in these patients could be helpful in supporting the<br />

parameters as calculated with the model.<br />

Tenofovir, an antihuman immunodefi ciency virus (HIV) drug, has activity against lamivudine-resistant<br />

HBV mutants. In Chapter 4.2 the effi cacy of tenofovir is described in<br />

patients with lamivudine-resistant hepatitis B. Two investigative approaches based on<br />

mathematical models of viral dynamics were applied: the individual nonlinear fi tting and<br />

the mixed-effect group fi tting approaches.<br />

Eleven chronic HBV patients on lamivudine for a median of 176 weeks (range: 72–382)<br />

with YMDD mutation-related HBV-DNA breakthrough received ‘add-on’ tenofovir 300<br />

mg once-daily, while maintaining their existing therapy. Sequential sera assessing HBV<br />

DNA levels were frequently taken during the fi rst 4 weeks of treatment and every 4<br />

weeks thereafter.<br />

Median baseline log HBV-DNA was 8.62. Tenofovir treatment resulted in a mean log<br />

HBV-DNA decline of 1.37 in the fi rst phase, 2.54 after 4 weeks, and 4.95 log HBV-DNA<br />

after 24 weeks. The median effectiveness of blocking viral replication in the individual

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