New data showed short interest over the past two-week period in Valeant Pharma (NYSE: VRX) increased 49.3% to 10,537,201 shares, Guggenheim analyst Louise Chen highlighted. Notably, the increase in short interest data was for the period ending 10/15/2015, nearly a week before Citron Research's "smoking gun" report on October 21. Citron disclosed its initial short position in VRX on September 28.

Some Specialty Pharma peers also saw large increase: Shire (NASDAQ: SHPG) short interest increased 47.3%, Zoetis (NYSE: ZTS) increased 21.2% and Horizon Pharma (NASDAQ: HZNP) short interest increased 8%. Allergan (NYSE: AGN) and Mallinckrodt (NYSE: MNK) each saw a drop.

Meanwhile, in large-cap biotech short interest in Biogen (NASDAQ: BIIB) fell 17.5% to 4,247,478 shares. Short interest in Amgen (NASDAQ: AMGN) rose 14.9% and short interest in Gilead (NASDAQ: GILD) rose 8.2%.