July 14 (HealthDay News) -- The widely prescribed blood-thinning drug heparin is associated with an increased risk of serious bleeding in patients who have suffered a cardioembolic stroke, new research shows.

But another thinning agent, warfarin, did not seem to have any harmful effects in the same group of patients.

This finding led the authors of a study published online Monday and in the September print issue of the Archives of Neurology to suggest that warfarin appears to be safe and could be started at any time while a patient is hospitalized.

According to the American Heart Association, a cardioembolic stroke occurs when a clot or other particle originally forms in the heart then travels to a narrowed artery in the brain.

This type of stroke represents about one-fifth of ischemic strokes, those which involve reduced blood flow to the brain, the researchers said.

Although current guidelines don't recommend giving anti-clotting therapy right after a cardioembolic stroke, most patients with this condition will end up needing such therapy. The question is when, and with what drug.

Warfarin can do the trick but often takes days to reach effective levels so, in the interim, is combined with other therapies.

For this study, researchers at the University of Texas Health Science Center at Houston reviewed the records of 204 patients who had had a cardioembolic stroke and were admitted to the hospital between 2004 and 2006.

Eight patients received no anti-clotting therapy at all; 88 received aspirin (a blood thinner) alone; 35 received aspirin and warfarin; 44 received heparin intravenously with warfarin; and 29 received a full dose of enoxaparin, a low-molecular-weight heparin then warfarin.

Participants who did not get full doses of heparin or enoxaparin instead received low-dose enoxaparin to prevent blood clots in the legs.

Five percent of patients had a progressive stroke (their conditions continued to decline even after the acute phase of the stroke was over); all but one of these cases occurred in the aspirin-only group.

In addition, patients receiving aspirin alone were more than 12 times as likely to have stroke progression compared with patients taking other types of therapies.

Eleven percent of patients experiencing bleeding into the brain tissue. Only three, however, were symptomatic, and all of these had been taking full-dose enoxaparin. Two patients taking heparin had systemic bleeding.

Adding enoxaparin or heparin to warfarin increased the risks of bleeding but could be considered in certain circumstances, the authors stated.

SOURCE: Archives of Neurology, press release, July 14, 2008