Obesity is a known risk factor for venous thromboembolism. But treating blood clots in overweight people poses another challenge. In theory, the distribution of blood thinners in the tissue may depend on a person’s size. So, in theory, blood thinners may be less effective in larger, obese, people. For this reason decisions about blood thinners in obese people may need to be different than for people of normal weight.
Oral Anticoagulants as Blood Thinners in Obese People
The oral direct factor Xa and factor II inhibitors are first line compared to Coumadin for many patients with pulmonary embolism, deep vein thrombosis or atrial fibrillation. But in the pivotal studies that got them approved, obese patients were either excluded or just uncommon. Still, in all their package inserts there is no specific recommendation for dose adjustment in patients who are overweight.
Having said that, there are concerns, especially in patients with BMI over 40 or a weight of over 120 Kg. Thus, the ISTH originally recommended against using these medications in patients who are so obese. They also recommended to measure drug-specific peak and trough levels if a patient still receives one of these medications.
This was in 2016. Then, by 2021, they updated their recommendation. In this document they offered more nuanced guidance. It seems that as of 2021, there were more data about rivaroxaban to treat acute venous thromboembolism. But for prevention, they recommended both apixaban and rivaroxaban. Then, they recommended not to use dabigatran, edoxaban, or betrixaban for VTE treatment and prevention.
Coumadin is Sometimes Still a Great Option
We have much data that Coumadin is safe and effective in obese people who require anticoagulation. So, sometimes offering Coumadin can be the best option, even in the era of oral factor Xa inhibitors. I have discussed this a bit in a video about “which blood thinner is best for me?“. Having said that, there are also data that point to the opposite. For instance, a retrospective analysis of the VENUS registry showed fewer bleeds with DOAC compared to Coumadin in obese patients.
Blood Thinners in Obese Patients after Bariatric Surgery
Coumadin is also a reasonable option after bariatric surgery. But not all bariatric surgery are the same. So we need to consider the exact type of surgery and its effect on medication absorption. However, in patients in whom we suspect that absorption is affected, we should choose Coumadin. Also, per the 2021 ISTH guidance that I mentioned above, perhaps using parenteral anticoagulation for several weeks after surgery and before considering a switch is the safest approach.