Letter by Machado-Alba et al Regarding Article, “Rivaroxaban Versus Dabigatran or Warfarin in Real-World Studies of Stroke Prevention in Atrial Fibrillation: Systematic Review and Meta-Analysis”

To the Editor:

We have reviewed with great interest the article by Bai et al¹ where the safety and effectiveness of rivaroxaban, dabigatran, and warfarin were compared for the prevention of thromboembolic events using real-world evidence. It was found that the effectiveness of rivaroxaban is superior to that of warfarin in new users with atrial fibrillation, although it was similar when the patient changed from warfarin to rivaroxaban.

Previously, it has been described that the effectiveness of the nonvitamin K oral anticoagulants versus warfarin can vary according to the geographic region where it is evaluated.² In Colombia, we lack studies comparing the effectiveness of the nonvitamin K oral anticoagulants versus warfarin in the prevention of thromboembolic events.

The Colombian Health System provides universal coverage of health services through 2 types of insurance: the first is paid by the user/employer and the second is subsidized by the state. Several procedures are necessary to access health services, and usually a large percentage of them are delayed by the insurers, which argue the legal structure of the system to justify the delays. The most critical services include dispensing of high-cost drugs, which leads to delays in treatment and optimal pathology control, generating a progressive and cumulative pattern of harmful consequences.³

Our research group has previously determined the prescribing patterns and costs of nonvitamin K oral anticoagulants in a population of 1310 patients from Colombia. The most prescribed was rivaroxaban (52.9%), being at the same time the most expensive of this group of medicines.⁴

Considering that adherence to therapy is fundamental to achieve adequate drug effectiveness,⁵ we performed a quick review of month-to-month dispensations of oral anticoagulants in the database of the largest drug dispenser in Colombia (Audifarma S.A.). From a population database of ≈3.5 million people, we identified 14 711 patients who received at least 3 dispensations in the period from January to December 2016. It was found that 63% (n=9272) of them had at least 1 dispensing delay of ≥15 days, meaning that ≈2 of 3 of anticoagulant users could remain for >2 weeks without medication.

This worrisome picture could possibly be explained by difficulties in access to the medicines and a poor adherence to therapy. In the case of nonvitamin K oral anticoagulants and warfarin, patients with anticoagulation because of atrial fibrillation will be unprotected from thromboembolic complications that could be effectively prevented.

The research by Bai et al¹ and the aforementioned findings should motivate further real-world studies to assess the outcomes of interest in populations with cultural, social, economic, and health services differences. These findings could help clinicians in selecting the best anticoagulation therapy for a given patient because they must not only consider their effectiveness but also other variables such as barriers that affect medication adherence, the accessibility, and the costs to the health system.