Abstract
The Food and Drug Administration recently approved two new classes of oral anticoagulants: direct thrombin inhibitors, dabigatran etexilate and factor Xa inhibitors, apixaban and rivaroxaban [1]. All these three drugs are for the treatment of nonvalvular atrial fibrillation with rivaroxaban also gaining approval for venous thromboembolism. Absorption of each drug is regulated by P-glycoprotein efflux transporters and is variable. The bioavailability of dabigatran etexilate is 7% with peak effect within two hours after administration. Apixaban has a 50% bioavailability with peak effect occurring 3–4 hours after administration and rivaroxaban has a bioavailability greater than 80% with peak effect occurring 2–4 hours after administration [1]. A P-glycoprotein is located on the apical membrane of enterocytes, act by pumping substrates back into the intestinal lumen, thereby limiting drug absorption. Its concentration gradually increases from the stomach to the distal part of the intestine. Above a certain concentration, efflux outpaces influx preventing absorption. All three drugs have warnings against co-administration with medications that induce P-glycoprotein expression, resulting in increased P-glycoprotein concentration
Highlights
The Food and Drug Administration recently approved two new classes of oral anticoagulants: direct thrombin inhibitors, dabigatran etexilate and factor Xa inhibitors, apixaban and rivaroxaban [1]
The most common intestinal diversion procedure is the Roux-en-Y gastric bypass. The consequences of this procedure are a 95% reduction in gastric capacity as well as a reduction in the functional length of the gastrointestinal tract from bypass of the duodenum and proximal jejunum. These changes augment the effect of P-glycoprotein on limiting drug absorption, similar to the effect medications have on inducing P-glycoprotein expression
We report a 41-year-old male admitted to the cardiac care unit with chest pain while taking dabigatran etexilate 150 mg twice daily and dofetilide 500 mg twice daily for atrial fibrillation
Summary
The Food and Drug Administration recently approved two new classes of oral anticoagulants: direct thrombin inhibitors, dabigatran etexilate and factor Xa inhibitors, apixaban and rivaroxaban [1]. He started dofetilide for uncontrolled atrial fibrillation about 18 months ago and reported compliance with both dofetilide and dabigatran etexilate, taking them earlier that day. This case raises an important issue related to the potential for impaired absorption of the novel oral anticoagulants (NOAC) after gastric bypass.
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