It doesn't look like this selloff is company specific to GILD. The index is down sharply. Check the quote on ishares nasdaq biotech (IBB). Also note the price action in pharmas like ACT, VRX. Note the price action in CELG.
For a cogent discussion of Valeant Stock, read the annual Investor Day Transcripts of the Sequoia Fund. You can do a Google search and find them. VRX is the fund's largest position, and the fund's talented money managers control a huge amount of stock for their clients: over three billion dollars worth including the fund's position. Also there is an excellent past article in The Globe and Mail - again, you can use Google to find it. You should also look at the open market insider purchases of this stock. I continue to be a long term holder of VRX.