All I can say is that not approved for is not the same as not prohibited.
What does..... what will AASLD say about that? My perception is that FDA and AASLD are not always congruent.
Here is what I think; there is no data on retreating Sovaldi nor Harvoni based failures w/ Viekira Pak.
Certainly the AASLD doesn't recommend it for past PI failures.
It is possible that some approved sort of re-treatment plan will be in place, based of hard data, trial results. Some people wont even meet the requirements of damage for current *approved* treatments, much less retreating with untested unapproved forms of TX.
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