Move aside, small-molecule drugs for common diseases. Three biologic medicines initially developed to treat rheumatoid arthritis—a joint disorder that afflicts just 1% of the population worldwide—are on track to top the sales charts this year. According to forecasts compiled by Thomson Reuters's pharmaceutical intelligence unit, Humira (adalimumab) and two comparable antibodies that also target tumor necrosis factor-alpha, a cytokine involved in rheumatoid arthritis, will lead the list.

Credit: Abbott Laboratories

The trio will topple the cholesterol drug Lipitor (atorvastatin) and the blood thinner Plavix (clopidogrel) to become the world's top-selling medicines in 2012. Despite the smaller patient populations targeted by these biologics, the higher prices they demand can still translate into a sizeable market share, explains analyst Saurabh Aggarwal, principal of Novel Health Strategies, a life sciences consulting firm based in Bethesda, Maryland. “The pricing is a big factor that's driving the high sales in these products,” he says.

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