23.10.2012 Views

View PDF Version - RePub - Erasmus Universiteit Rotterdam

View PDF Version - RePub - Erasmus Universiteit Rotterdam

View PDF Version - RePub - Erasmus Universiteit Rotterdam

SHOW MORE
SHOW LESS

You also want an ePaper? Increase the reach of your titles

YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.

Chapter 1<br />

20<br />

The extended non-linear PD-models describing HBV DNA during and after therapy can<br />

be fi tted with available statistical software in two ways: (1) separately for each patient<br />

with non-linear regression and (2) combined for all patients with mixed non-linear methods<br />

adding random effects to obtain individual patient curves.<br />

Pegylated interferon behaves different than NA’s. The drug is standard injected once a<br />

week for 48 weeks and the injection of one dose of pegylated interferon α-2b (PEG-IFN)<br />

results in a decrease of hepatitis B viral load, followed by a slow increase as the drug<br />

concentration in the blood declines (see fi gure). Until now it has been assumed that the<br />

effectiveness of the drug stayed constant between injections, but with the observed<br />

increase of viral load at the end of the week, new models are necessary to interpret and<br />

describe viral kinetics.<br />

When treated with PEG-IFN the biphasic model is not adequate to describe the pattern<br />

of the HBV DNA and more complex models are required. First the drug concentration<br />

is assessed with a one-compartment model and the results incorporated in the model<br />

describing the viral load during the fi rst week (fi gure 4). As a result, the PEG-IFN concentration,<br />

the viral load and also the effectiveness during one week after one injection<br />

can be fi tted. Assuming that the drug concentration and the viral load pattern after<br />

the fi rst injection repeats itself after each injection, the viral and drug kinetics are fi tted<br />

with a periodical continuation during the fi rst month. The fi tted concentration and viral<br />

decline allows for comparison of biologically relevant patient characteristics, such as<br />

body weight and HBV genotype, which may be important for future treatment protocols.<br />

Similar to the analysis of the pharmacokinetic of the NA either non-linear regression<br />

analysis per subject or non-linear mixed regression analysis on all subjects with random<br />

effects on the parameters can be applied.<br />

PEG-IFN<br />

concentration<br />

viral load<br />

0 1 2 3 4 5 6 7<br />

days<br />

Figure 4. The patterns of interferon concentration and viral load after on injection of PEG-IFN.

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!