The one problem Merck (NYSE:MRK) investors feared most in 2012 was Singulair's patent expiration. This asthma medication, which reigned as the company's top-selling product for more than six years, lost U.S. exclusivity last August. Merck's top line took a significant hit in the fourth quarter after year-over-year Singulair sales plunged by more than 65%, but investors can now breathe a sigh of relief and focus on other issues... right?

Wrong. More patent expirations are on the way for this titan of the pharmaceutical industry, and our health care analyst dives into this issue in the following video.

Max Macaluso, Ph.D. has no position in any stocks mentioned. The Motley Fool has no position in any of the stocks mentioned. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.