We regularly rank drugs by sales: Top-selling cancer treatments, top-selling diabetes drugs, top-selling heart meds--you get the picture. And if you follow the industry, you know the world's biggest prescription products already. AbbVie's ($ABBV) Humira, for one, which brought in $12.5 billion last year. Here's a new one for you: 10 companies count on one top product to supply a major chunk of their sales, the business news site Quartz calculates. And several of those are either anticipating some serious pain from a near-term patent expiration, or already suffering from competition. Report