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Chapter 4.3<br />
222<br />
13-14 This model takes the decreasing effi cacy of PEG-IFN α-2b at the end of the week<br />
into account during once-weekly administration. We observed a signifi cant correlation<br />
between the AUC of the PEG-IFN α-2b concentration and body mass index (BMI) and a<br />
correlation between sex and the AUC of PEG-IFN α-2b. Based on these fi ndings, weightbased<br />
PEG-IFN α-2b dosing should also be considered in the treatment of chronic<br />
hepatitis B to optimize drug availability as is the standard in hepatitis C treatment. 20-21<br />
However, despite the infl uence of BMI on the pharmacokinetic constants of PEG-IFN<br />
α-2b, no clear effect of the PEG-IFN α-2b concentration was observed on treatment<br />
outcome or decline in viral load, as previously shown for PEG-IFN α-2a. 22 Furthermore,<br />
treatment of chronic hepatitis B patients with escalating doses of both PEG-IFN α-2a<br />
and α-2b did not lead to a better treatment outcome in chronic hepatitis B. 5, 16<br />
Next we incorporated the pharmacokinetic model for multiple weekly PEG-IFN α-2b<br />
injections proposed recently 13-14 in a combined pharmacokinetic-pharmacodynamic<br />
model. Viral kinetics were modelled using equations 3-5 We were able to use per patient<br />
PEG-IFN α-2b pharmacokinetics as well as viral kinetics data in 19 patients of the PEG-<br />
IFN α-2b monotherapy group. With this approach, it was possible to fi t the viral decline<br />
during the fi rst month of PEG-IFN α-2b monotherapy in patients with HBeAg-positive<br />
chronic hepatitis B. The maximum antiviral effectiveness of PEG-IFN α-2b monotherapy,<br />
εmax , was 70% and this is slightly lower than the antiviral effectiveness (83%) of PEG-IFN<br />
α-2b 100/200 μg in HBeAg negative chronic hepatitis B patients in the study by Sypsa<br />
et al., probably due to the lower PEG-IFN dose given. 16 There was no clear association<br />
between the antiviral effectiveness and several baseline factors, only older patients<br />
showed a slightly reduced maximal antiviral effectiveness (p=0.046). This antiviral effectiveness<br />
is lower compared to the estimated antiviral effectiveness of approximately<br />
92-99% for nucleos(t)ide analogues. 23-26 In the combination therapy group, viral load<br />
showed a biphasic decline pattern as a result of the addition of lamivudine. This pattern<br />
has already been extensively described in chronic hepatitis B patients treated with<br />
nucleos(t)ide analogues and therefore we did not model viral decline in the combination<br />
therapy group. 15, 24-26<br />
In the fi rst week, there was a pronounced decline in viral load in the combination therapy<br />
group and after one month of treatment there was a 2.94 log10 copies/ml decline in viral<br />
load. In the monotherapy group, probably as a result of the decline in drug concentration<br />
associated with once-weekly administration of PEG-IFN α-2b, we observed only<br />
a minimal decline in viral load with a rise towards the end of the week as also recently<br />
reported by Sypsa et al. in HBeAg-negative chronic hepatitis B 16 Therefore, there was<br />
only a limited decrease in viral load at the end of the fi rst week of treatment in the<br />
monotherapy group and no clear biphasic decline pattern was observed as seen during