Blood-thinners need closer monitoring: report

By David Douglas

NEW YORK (Reuters Health) - Patients taking blood-thinning pills (also called anticoagulants) for long periods of time need to be closely monitored by their doctor, researchers caution based on a pooled analysis of studies that recorded instances of hemorrhage (bleeding) and blood clots in people taking blood thinners.

Blood-thinners are used to prevent blood clots in people with a variety of conditions; for example, blood clots in veins, artificial heart valves, and chronic heart rhythm disturbances. The dosage of these drugs must be closely gauged to avoid causing the blood to be too thin, which may cause bleeding, or not thin enough, permitting clots to form, which can lead to stroke and heart attack.

Doctors monitor blood-thinner treatment by keeping tract of a patient's "international normalized ratio" or INR.

Dr. Natalie Oake of Ottawa Hospital and colleagues analyzed data from 45 studies containing INR information and reports of hemorrhages and blood clots in patients taking blood thinners. They found that INRs fell outside the optimal range more than one-third of the time. This increases the likelihood of adverse events, the team notes in a report in the Canadian Medical Association Journal.

The team found that 44 percent of hemorrhages took place when INRs were above the therapeutic range. Conversely, 48 percent of clotting events occurred when INRs were below the therapeutic range.

"Improved anticoagulation control could decrease the likelihood of almost half of all adverse events associated with anticoagulants taken orally," the researchers conclude.

SOURCE: Canadian Medical Association Journal May 22, 2007.