Compared with conventional anticoagulants, both dabigatran and rivaroxaban conferred small but statistically significant increases in the risk of major gastrointestinal bleeding in a systematic review and meta-analysis of randomized trials reported in the November issue of Clinical Gastroenterology and Hepatology. (doi: 10.1016/j.cgh.2017.04.031)
But other novel oral anticoagulants (NOACs) showed no such effect compared with warfarin, aspirin, or placebo, reported Corey S. Miller, MD, of McGill University, Montreal, and his associates. “The potentially increased risk of GI bleeding associated with dabigatran and rivaroxaban observed in some of our subgroup analyses merits further consideration,” they wrote.
The NOACs (also known as non–vitamin K antagonist oral anticoagulants) help prevent stroke in patients with atrial fibrillation and prevent and treat venous thromboembolism. However, large AF trials have linked all except apixaban to an increased risk of major GI bleeding compared with warfarin. Dabigatran currently is the only NOAC with an approved reversal agent, “making the question of GI bleeding risk even more consequential,” the authors wrote.
They searched the MEDLINE, EMBASE, Cochrane, and ISI Web of Knowledge databases for reports of randomized trials of NOACs for approved indications published between 1980 and January 2016, which identified 43 trials of 166,289 patients. Most used warfarin as the comparator, but one study compared apixaban with aspirin and six studies compared apixaban, rivaroxaban, or dabigatran with placebo. Fifteen trials failed to specify bleeding sources and therefore could not be evaluated for the primary endpoint, the reviewers noted.
In the remaining 28 trials, 1.5% of NOAC recipients developed major GI bleeding, compared with 1.3% of recipients of conventional anticoagulants (odds ratio, 0.98; 95% confidence interval, 0.80-1.21). Five trials of dabigatran showed a 2% risk of major GI bleeding, compared with 1.4% with conventional anticoagulation, a slight but significant increase (OR, 1.27; 95% CI, 1.04-1.55). Eight trials of rivaroxaban showed a similar trend (bleeding risk, 1.7% vs. 1.3%; OR, 1.40; 95% CI, 1.15-1.70). In contrast, subgroup analyses of apixaban and edoxaban found no difference in risk of major GI bleeding versus conventional treatment.
Subgroup analyses by region found no differences except in Asia, where NOACs were associated with a significantly lower odds of major GI bleeding (0.5% and 1.2%, respectively; OR, 0.45; 95% CI, 0.22-0.91).
Most studies did not report minor or nonsevere bleeds or specify bleeding location within the GI tract, the reviewers noted. Given those caveats, NOACs and conventional anticoagulants conferred similar risks of clinically relevant nonmajor bleeding (0.6% and 0.6%, respectively), upper GI bleeding (1.5% and 1.6%), and lower GI bleeding (1.0% and 1.0%).
A post hoc analysis using a random-effects model found no significant difference in risk of major GI bleeding between either rivaroxaban or dabigatran and conventional therapy, the reviewers said. In addition, the increased risk of bleeding with dabigatran was confined to the RELY and ROCKET trials of AF, both of which exposed patients to longer treatment periods. Dabigatran is coated with tartaric acid, which might have a “direct caustic effect on the intestinal lumen,” they wrote. Also, NOACs are incompletely absorbed across the GI mucosa and therefore have some anticoagulant activity in the GI lumen, unlike warfarin or parenteral anticoagulants.
The reviewers disclosed no funding sources. Dr. Miller and another author reported having no conflicts of interest. One author received research grants and speaker honoraria from Boehringer Ingelheim Canada, Bayer Canada, Daiichi Sankyo, Bristol Myers Squibb, and Pfizer Canada; another author disclosed serving as a consultant to Pendopharm, Boston Scientific, and Cook.