Pharmacodynamics of PEG-IFN-α-2a in HIV/HCV co-infected patients: Implications for treatment outcomes

Background & Aims The pharmacokinetics and pharmacodynamics of pegylated-interferon-α-2a (PEG-IFN) have not been described in HCV/HIV co-infected patients. We sought to estimate the pharmacokinetics and pharmacodynamics of PEG-IFN and determine whether these parameters predict treatment outcome. Methods Twenty-six HCV/human immunodeficiency virus (HIV)-co-infected patients were treated with a 48-week regimen of PEG-IFN (180μg/week) plus ribavirin (11mg/kg/day). HCV RNA and PEG-IFN concentrations were obtained from samples collected until week 12. A modeling framework that includes pharmacokinetic and pharmacodynamic parameters was developed. Results Five patients discontinued treatment. Seven patients achieved a sustained virological response (SVR). PEG-IFN concentrations at day 8 were similar to steady-state levels ( p =0.15) and overall pharmacokinetic parameters were similar in SVRs and non-SVRs. The maximum PEG-IFN effectiveness during the first PEG-IFN dose and the HCV-infected cell loss rate ( δ ), were significantly higher in SVRs compared to non-SVRs (median 95% vs. 86% [ p =0.013], 0.27 vs. 0.11day −1 [ p= 0.006], respectively). Patients infected with HCV genotype 1 had a significantly lower average first-week PEG-IFN effectiveness (median 70% vs. 88% [ p =0.043]), however, 4- to 12-week PEG-IFN effectiveness was not significantly different compared to those with genotype 3 ( p =0.114). Genotype 1 had a significantly lower δ compared to genotype 3 (median 0.14 vs. 0.23day −1 [ p =0.021]). The PEG-IFN concentration that decreased HCV production by 50% (EC 50 ) was lower in genotype 3 compared to genotype 1 (median 1.3 vs. 3.4 [ p =0.034]). Conclusions Both the HCV-infected cell loss rate ( δ ) and the maximum effectiveness of the first dose of PEG-IFN-α-2a characterised HIV co-infected patients and were highly predictive of SVR. Further studies are needed to validate these viral kinetic parameters as early on-treatment prognosticators of response in patients with HCV and HIV.