Rising drug costs have always been a concern to employers, but one major driver of health care costs might be drug spending that's not even part of your pharmacy benefit.

Specialty drugs have emerged as a significant concern for employer-sponsored health plans, because these costs are often hidden in medical claims, rather than pharmaceutical billing, and because they often are extremely expensive. Specialty drugs that treat multiple sclerosis, cancer, or heart disease can range in cost from $50,000 to more than $100,000 a year. And because they are often administered in clinics or hospitals, they fall under medical benefit claims 47 percent of the time, according to data in a brief by Health Affairs.

The high cost of specialty drugs has drawn notice from President Obama, who has suggested allowing Medicare to negotiate prices for such drugs, and the editorial page of the New York Times. In a separate article, the Times noted that Medicare beneficiaries and government programs account for 25 to 33 percent of spending on specialty drugs.