Big pharma and blue-chip biotech stocks rarely lose 8% of their value in a single week, but that's exactly what happened to AbbVie (NYSE: ABBV) last week. The drugmaker's stock sank after FDA Commissioner Scott Gottlieb stated that he is working toward making it easier for knock-off biologic drugs called biosimilars to enter the market, which could become a significant threat to AbbVie's top line. AbbVie's top-selling anti-inflammatory medicine, Humira, tends to make up over 60% of its total revenue on annual basis, and the drug's main ingredient has already lost patent protection in the United States.To ward off would-be copycats, AbbVie has built a massive patent portfolio covering nearly every aspect of how the drug is manufactured, and more recently, the biotech signed licensing agreements with the likes of Amgen (NASDAQ: AMGN) and Mylan (NASDAQ: MYL) to postpone the U.S.