Is there a reason that you're considering an interferon dose reduction?? If neutropenia, the following applies to Inf/Riba, not the PIs.
Neutropenia frequently complicates IFN-based antiviral therapy for hepatitis C [14]. The relationship between neutropenia and infectious complications in this instance is not well described. In the absence of data, reduction in IFN dose and/or G-CSF dose for those who develop neutropenia while undergoing IFN-based therapy for HCV infection are often initiated in clinical practice, as suggested in treatment guidelines [6] and mandated in most clinical trials [15]. Reduction of IFN dose is well accepted to have a detrimental effect on the rate of sustained virological response [2]. Despite G-CSF use, there is little evidence that it results in increased sustained virological responses [16, 17] or a reduced rate of infection. Furthermore, it is expensive.
http://cid.oxfordjournals.org/content/42/12/1674.full#ref-6
The current protocols provide for reduction of riba or the discontinuation of SOC.
I don't believe there is much data (on IFN reductions), if any. There is likely ample theory and evidence which prevented such trials occurring.
The reason, I believe is that the PI's work effectively against the "wild type" virus, but end up generating PI resistant stains which one's enhanced (with IFN) immune response can often defeat. If you take IFN out of the equation there is not much to defeat those resultant PI resistant virii.
willy