Dallas ? Heart patients who had drug-coated stents inserted to prop open blocked coronary arteries should stay on anti-clotting drugs for at least a year, several doctor groups said in an advisory issued Tuesday.

The advisory recommends that doctors tell their patients to take an anti-clotting drug like Plavix and aspirin for a year to reduce the risk of clotting, which could lead to a heart attack or death. The long-term safety of Plavix in stent patients has not been established.

Drug-coated stents often are chosen over bare metal stents because they slowly release medication that reduces the chance of arteries reclogging, which can mean follow-up surgery.

However, the newer stents mean a small but significant increased risk of clotting.

The new advisory cited research showing blood clots in up to 29 percent of patients who stopped anti-clotting drugs early after receiving a drug-coated stent.