A new compound can quickly counteract the action of an emerging class of drugs, offering a way to reverse the drugs' actions if a patient develops serious side effects, U.S. researchers said on Sunday.

They designed the compound to work with a new blood-thinner being developed for heart patients undergoing angioplasty to clear out blocked arteries.

Such patients need to take blood thinners to prevent blood clots during surgery, but bleeding is a common side effect.

Having an antidote on hand would make the treatments safer, said Bruce Sullenger of Duke University Medical Center, whose study was published in the journal Nature Medicine.

But instead of just reversing the effects of the blood thinner, the antidote agent appears to work against a whole new class of drugs called aptamers.

Most drugs target proteins. The type of drugs we're talking about are ribonucleic acids (RNAs) that target proteins, Sullenger said in a telephone interview.

Normally in our body we don't have these types of molecules outside of cells, Sullenger said.

The antidote agent takes advantage of this, targeting only nucleic acid compounds circulating freely outside the cells.

What we are doing is using agents that will sop up any nucleic acid. It's basically acting like a sponge, Sullenger said. We put the sponge in the one compartment where the drug is, he said.

The team tested these antidote molecules against eight different aptamer compounds in test tubes and found it controlled the activity of all of them.

They also tried it in a pig that had been given an aptamer blood thinner compound. We showed you could rapidly reverse that blood-thinning effect, he said.

So far, Pfizer's Macugen, a treatment for age-related macular degeneration, is the only aptamer drug currently approved for sale by the U.S. Food and Drug Administration, but Sullenger said several others are being tested.

Sullenger said his blood thinner, called REG1, is being studied in people through a company he founded called Regado Biosciences in Durham, North Carolina.

He thinks having an antidote to this emerging class of drugs would make them especially safe.

We predict that this advance will significantly expand the number of diseases that can be more safely treated using antidote-controllable agents, he said.