(January 25, 2008 - Insidermedicine) Idraparinux, a synthetic oligosaccharide anticoagulant, causes more bleeding than vitamin K antagonists when used in patients with atrial fibrillation, although the efficacy of both for preventing thromboembolic stroke is similar, according to a study published in The Lancet.

Here are some recommendations regarding the use of antithrombotic therapy from the American College of Chest Physicians:

•    Patients with persistent or paroxysmal atrial fibrillation at high risk for stroke should receive anticoagulation with an oral vitamin K antagonist, to a target international normalized ratio (INR) of 2.5 (range 2.0 to 3.0).

•    In the absence of other risk factors for stroke, patients with persistent or paroxysmal atrial fibrillation aged 65 to 75 should receive antithrombotic therapy with either an oral vitamin K antagonist (target INR, 2.5; range 2.0 to 3.0) or aspirin 325 mg/day.

•    In the absence of other risk factors for stroke, patients with persistent or paroxysmal atrial fibrillation under 65 years of age should receive aspirin, 325 mg/day.

Researchers from the Academic Medical Centre in Amsterdam and the AMADEUS Investigators Group randomized patients with atrial fibrillation to treatment with 2.5 mg weekly subcutaneous injections of idraparinux or adjusted dose vitamin K antagonists. Randomization was discontinued, however, after enrolling over 4,500 patients because of higher bleeding rates in the idraparinux group.

While both treatments prevented thromboembolic stroke equally well, 346 patients taking idraparinux experienced clinically-relevant bleeding, compared with only 226 of those taking vitamin K antagonists. This translates to a 74% increased bleeding rate among those taking idraparinux. Among these cases were 21 instances of intracranial bleeding in the idraparinux group and only 9 in the vitamin K antagonist group. Elderly patients and those with renal impairment were at greatest risk for bleeding complications.

Today's research highlights the fact that vitamin K antagonists, despite the inconvenience of therapy, remain the best option for preventing thromboembolism in patients with atrial fibrillation. While the novel anticoagulant idraparinux is as effective and easier to administer, it significantly increases the risk of clinically-relevant bleeding.

For Insidermedicine in Depth, I'm Dr. Susan Sharma.