Washington ? If you buy medicine through Medicare’s prescription drug program, you could be paying too much.

The taxpayers who finance Medicare aren’t doing too well, either.

Insurance companies involved in the Medicare prescription drug benefit have overcharged subscribers and taxpayers by several billion dollars, according to the inspector general for the Department of Health and Human Services. Eighty percent of the participating insurance companies owe the program an estimated $4.4 billion for 2006 alone.

Medicare, however, has been slow to do something about it. In fact, the agency doesn’t even know how much money the insurance companies owe taxpayers because it hasn’t begun most of the financial audits needed to determine that.

“It shows a mindset that could care less about wasting taxpayer money, that has no problem with padding profits of drug companies with hard-earned taxpayer dollars,” said Sen. Claire McCaskill, a Missouri Democrat.

McCaskill, a former state auditor, has asked the Centers for Medicare and Medicaid Services, which administers the program, to explain why so many audits haven’t been done and how it plans to collect the $4.4 billion.

Medicare is the federal health insurance program for people 65 and older. The optional prescription drug benefit, which subsidizes the costs of medicine for subscribers, was the subject of an intense political debate before Congress enacted the program in 2003.