Pradaxa (dabigatran) is an oral factor Xa inhibitor that prevents clotting and has been approved as an effective alternative to the anti-coagulant warfarin (Coumadin). The marketed advantage for Pradaxa is that blood tests are not required to monitor dosage and its effectiveness. The FDA only approved the drug for prevention of thromboembolic stroke in patients with atrial fibrillation. The RE-LY Study used for FDA approval showed that dabigatran was as effective as warfarin. However, within 12 weeks of its approval in October 2010, it was reported that dabigatran was responsible for more serious adverse events than 98.7% of all other medications.
Only 36% of Pradaxa prescriptions in the U.S. were written for its approved use, atrial fibrillation. Off-label use for general prevention of blood clots or stroke accounted for 46% of prescriptions. Although the RE-LY study only tested doses of 110 mg and 150 mg in patients, the FDA approved doses in amounts of 150 mg and 75 mg, even though the 75 mg dose was never tested in the study populations. The use of Pradaxa is increasing rapidly, physicians are prescribing the medication for unapproved uses and its anticoagulant action is hard to measure. But there is an even more troubling problem with Pradaxa.
Unlike warfarin, there is no reversal agent for its anticoagulation effect in cases of overdose. Agents typically used to undo the anticoagulation of warfarin and heparin have no effect. Hemodialysis the only currently available way to inactivate it, and hemodialysis not an option when there is an intracerebral bleed. There have already been published case reports in the setting of trauma where there was documented rapid deterioration and death because of the lack of a reversal agent.
Unanticipated safety risks are emerging. A review of published trial data shows an approximately 30% increased risk of heart attack and acute coronary syndrome with dabigatran usage. These additional risks do not appear to have been factored into the decision to approve Pradaxa for use.
Warfarin has a long history of use in patients. It's safety, efficacy, testing procedures and risks are well known. It is rapidly reversible if over-anticoagulation occurs. Pradaxa is a new class of drug with new risks and difficulties being discovered as its use is increased. Physicians should be extraordinarily conservative in considering its use instead of warfarin. It is marketed to doctors and patients to be as effective as warfarin without the need for repeated blood tests. However, patients need to ask their physicians if the convenience of no testing is worth undertaking the risk.