An Observational Study Compared Myocardial Infarction / Heart Attack Risks As Between The Use Of Newer Blood Thinners And The Use Of Warfarin
In the US, there are currently four direct-acting oral anticoagulants (DOACs), a relatively new class of blood thinners, approved for the prevention of stroke in patients with atrial fibrillation (AF):
- Pradaxa (dabigatran) -- approved by FDA in 2010 -- Boehringer Ingelheim Pharmaceuticals
- Xarelto (rivaroxaban) -- approved by FDA in 2011 -- Janssen Pharmaceuticals
- Eliquis (apixaban) -- approved by FDA in 2012 -- Pfizer and Bristol-Myers Squibb
- Savaysa (edoxaban) -- approved by FDA in 2015 -- Daiichi Sankyo
To date, there have been various medical journal articles published with conflicting results regarding the risk of acute myocardial infarction (AMI), or heart attack, with the use of these DOACs. This has especially been the situation with Pradaxa -- classified as a "IIa inhibitor" (as opposed to an "Xa inhibitor") -- in comparison with vitamin K antagonists (VKAs), such as warfarin.
In March 2017 the British Journal of Clinical Pharmacology published this article, "Risk of myocardial infarction in patients with atrial fibrillation using vitamin K antagonists, aspirin or direct acting oral anticoagulants", which reports on the first retrospective cohort study to compare the risk of AMI with use of DOACs with that associated with VKA use.
The bottom line is that the medical researchers conducting this study found a two-fold increase in the risk of heart attacks with use of Pradaxa (dabigatran) and Xarelto (rivaroxaban) in comparison with warfarin in patients using those drugs for atrial fibrillation (AF) therapy.
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Specifically, from the Results section of the Abstract for this March 2017 medical journal article: "The risk of AMI was doubled when we compared current use of DOACs with current use of VKAs [adjusted HR 2.11; 95% confidence interval (CI) 1.08, 4.12]...."
In more detail, from the Discussion part of the full article:
Our results differed from the randomized controlled Rivaroxaban Once Daily Oral Direct Factor Xa Inhibition Compared with Vitamin K Antagonism for Prevention of Stroke and Embolism Trial in Atrial Fibrillation (ROCKET AF) trial with rivaroxaban vs. warfarin (risk of AMI: HR 0.81; 95% 0.63, 1.06)  but were in line with the randomized controlled RE-LY trial with dabigatran vs. warfarin (risk of AMI: HR 1.38; 95% CI 1.0,1.91) . A major weakness of these clinical trials is their limited external validity. They do not reflect a real-life population, as patients with AF currently using these drugs have a different risk profile to patients seen in daily clinical practice....
In conclusion, our cohort study identified a twofold increase in the risk of AMI when using DOACs, [Xarelto (rivaroxaban)] or [Pradaxa (dabigatran)], in comparison with VKAs, in AF therapy in real-world patients. In addition, our results showed that in AF patients, the risk of AMI with current use of aspirin as monotherapy is higher than with current use of VKAs. VKAs probably have greater beneficial effects on AMI than DOACs. Ongoing research is needed as the use of DOACs increases in the population.
While this observational study reports that there is a correlation between the use of Xarelto (rivaroxaban) or Pradaxa (dabigatran) with an increased risk for myocardial infarction (MI), or heart attack, it is important to keep in mind that correlation does not prove causation.
Rather, in order to definitively answer the question "Do direct oral anticoagulants (DOACs) increase the risk for myocardial infarction (MI), or heart attack", we will need a well-designed study. One hopes that Boehringer Ingelheim Pharmaceuticals (Pradaxa) or Janssen Pharmaceuticals (Xarelto) or one of the other responsible drug companies have such a drug-safety study currently underway or planned to begin soon.
Of course, we will continue to monitor the medical literature for developments concerning the safety profile of Pradaxa, Xarelto, Eliquis, and Savaysa.
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