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15-07-2009 | Cardiology | Article

Optimal INR suggested for OAT indications


Free abstract

MedWire News: The optimal intensity of oral anticoagulant therapy (OAT) varies with indication, say researchers after calculating international normalized ratio (INR)-specific incidence rates for bleeding and thrombosis among different patient populations.

“Now that we have defined the presumed optimal intensity of oral anticoagulation for patients with mechanical heart valve prostheses, atrial fibrillation (AF), and after myocardial infarction (MI), testing these ranges in new clinical trials should be considered,” write Frits Rosendaal (Leiden University Medical Center, The Netherlands) and co-workers.

“These trials could compare current target ranges with the optimal intensity levels we found and provide us with a final answer as to which INR level is safest for patients at high risk for arterial thromboembolism.”

To improve the risk–benefit ratio of OAT, the team determined the rate of untoward cardiovascular events (major thromobembolism and major bleeding) in 4202 patients attending Leiden Anticoagulation clinic with mechanical heart valves, AF, or MI between 1994 and 1998, a total of 7788 patient years.

Of the 3226 reported hospital admissions, 306 were due to an untoward event, the team reports in the Archives of Internal Medicine.

The rate of untoward events was around 4%, at 4.3 events per year for patients with mechanical heart valve prostheses, 4.3 events per year for patients with AF, and 3.6 events per year for patients receiving OAT after MI.

Moreover, the intensity of OAT associated with the lowest rate of untoward events was calculated to be an INR of 2.5–2.9 for patients with mechanical heart valves, rising to 3.0–3.4 for those with AF, and 3.5–3.9 for patients treated after MI.

While noting the small number of events during the trial and limited use of patient and clinical markers, the researchers say their study is strengthened by use of actual achieved INR levels rather than target INR.

They add: “We performed a study in the routine setting of an anticoagulation clinic, preventing bias from nonroutine, more intense monitoring. For this reason, the study results can easily be applied to day-to-day practice.”

MedWire ( is an independent clinical news service provided by Current Medicine Group, a part of Springer Science+Business Media. © Current Medicine Group Ltd; 2009

By Lynda Williams

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