Letters To The Editor

In reply: Dabigatran

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In Reply: Dabigatran has gained significant popularity in the United States. From its approval in October 2010 and through August 2011, approximately 1.1 million prescriptions for it were dispensed, and 371,000 patients received it from US outpatient retail pharmacies.1 We appreciate the letters from Drs. Pazmiño and Hirsch and believe there are reasons to be vigilant when using dabigatran.

In response to the letter from Dr. Pazmiño, we agree with his concerns and have covered them in our review. We would like to emphasize that our review was intended to help US clinicians understand this new drug and was not restricted to the RE-LY trial. The limitations of the trials of dabigatran to date (including the lack of patients with renal impairment in the RE-LY trial) have been mentioned in many articles, including ours. Please see the section TOPICS OF FUTURE INTEREST.2

The FDA did not recommend any dose adjustment for patients with moderate renal impairment (creatinine clearance 30–50 mL/min), as it was convinced that the 150-mg dose had a superior risk-benefit profile, even for patients with a higher risk of bleeding, compared with the 110-mg dose.3 It is hard for us to comment on the specific reasoning behind the FDA’s approval for using 75 mg of dabigatran in patients with creatinine clearance between 15 and 30 mL/min. However, we know this was based on pharmacokinetic and pharmacodynamic modeling and not on efficacy and safety data.3 With respect to dosing and monitoring, we did stress this point in our article, stating that the use of dabigatran obviates the need for routine laboratory monitoring. However, one may measure the drug’s activity in certain situations (suspected overdose, bleeding, need for emergency surgery, impaired renal function, pregnancy, and obesity, and in children). Please see the section DOES DABIGATRAN NEED MONITORING? CAN IT EVEN BE MONITORED? in our review.2

Dr. Pazmiño suggests renal, hematologic and hepatic variables should be monitored before and after starting dabigatran. We agree that renal function should be monitored and have covered this point. Please see the section WHO SHOULD NOT RECEIVE DABIGATRAN.2 Hematologic and hepatic variables can be monitored if a clinician decides to do so, but this is not limited specifically to dabigatran. Also, to clarify, dabigatran is not approved for those with stage 5 chronic kidney disease. And we share his concern about the lack of experience with this new drug, and we included a word of caution in the section ADVANTAGES AND DISADVANTAGES OF DABIGATRAN.2

We agree with Dr. Hirsch’s concerns about recombinant factor VIIa. We are not recommending its use as a routine practice but as an available option. Our article was a global review on dabigatran, and our aim was to cover the best available evidence and treatment options in a comprehensive way. However, in response to Dr. Hirsch’s comments, the systematic review by Yank et al4 drew its data from 16 randomized controlled trials but excluded patients on anticoagulants (except for those in a few observational studies), and factor VIIa was compared with placebo.4 So these findings are not applicable to patients with dabigatran-related bleeding, and to draw any definite conclusion would not be correct. If recombinant factor VIIa has failed to show a benefit in terms of a lower mortality rate, we could also point out that there was no mortality benefit seen in reversing warfarin anticoagulation in patients with acute intracranial hemorrhage with the use of vitamin K, fresh-frozen plasma, or prothrombin complex concentrate.5 This should not lead one to stop using these treatments.

Clinicians are well accustomed to managing warfarin- or heparin-related bleeding using specific antidotes. It is very important to understand the mechanism of action of dabigatran, and to realize that there is no antidote. Recombinant factor VIIa is a potent hemostatic agent, and there are many published case reports and case series highlighting its efficacy in preventing bleeding.6–12 It is used when all other options are exhausted. It is never a routine practice: it is always a last resort a clinician takes to prevent catastrophic bleeding. We believe economic concerns are very important, but it will be difficult to extrapolate a specific benchmark while treating for an individual case. At present, it seems unlikely that a randomized trial of recombinant factor VIIa will be conducted, and guidance is to be based on available animal studies and clinical anecdotes. A recent review on reversing anticoagulation therapy13 proposes treating major bleeding complications of direct thrombin inhibitors with activated prothrombin complex and recombinant factor VIIa.13

We acknowledge that serious, even fatal bleeding events have been reported with dabigatran. The FDA is evaluating postmarketing reports and is also using an active surveillance system to compare new users of dabigatran and warfarin with respect to the likelihood of their being hospitalized for bleeding.1 With time and experience, we will learn more.

Finally, as with any new drug, the absence of data on long-term safety and efficacy is an important issue and should be considered when prescribing this new medication.

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