My logic was based on keeping IDX320 in the pipeline. Perhaps it's flawed because nobody would take a chance partnering an orphan PI which failed combining safely with a nuke. The safety of second generation PI's already remains questionable AKA ITMN-191 in the INFORM study. A drug interaction problem could also lead IDX184 to be blacklisted and/or be partnered on less favorable terms.
ITMN-191 is more appropriately classified as a 1st gen HCV PI IMO. IDX320 is more along the lines of a 3rd gen HCV PI given the higher potency and pan-genotypic coverage. ACH-1625 is an example of what I think of as a true 2nd gen HCV PI (much higher potency compared to 1st gen HCV PIs but lacking the pan-genotypic coverage of a 3rd gen HCV PI). To date, ACH-1625 has had a clean safety profile through all of the Phase 1 trials. (The Phase 2a trial starts at the end of this month.)