Sales of Humira, which is the world's top-selling prescription drug, increased 18 percent to $3.1 billlion. Humira is approved to treat more than a dozen conditions including rheumatoid arthritis, psoriasis and Crohn's Disease. But it will start losing patent protection next year and could eventually face competition from Amgen Inc., which is developing a biosimilar version of the drug. That has focused attention on other AbbVie drugs with blockbuster potential, including Viekira Pak, a new hepatitis C medication approved in the U.S. in December.