LAUSR

To the Editor: Long-term oral anticoagulation is recommended to prevent stroke and systemic embolism in patients with atrial fibrillation (AF) [1]. Non-vitamin K antagonist oral anticoagulants (NOACs) have emerged as the preferred choice in these patients [2].However, published data has recently demonstrated that dabigatran-PPI interaction significantly reduces dabigatran plasma levels [3, 4], most probably mediated through the effect on gastric pH [5]. This implies that dabigatran would not be highly soluble also among posttotal gastrectomy patients, as they have no gastric acid secretion. Nevertheless, there are no data about post-total gastrectomy patients with non-valvular atrial fibrillation treated with dabigatran. A 68-year-old post-total gastrectomy patient due to the diffuse large B cell lymphoma, in complete remission, and with permanent AF, was admitted to the Department of Internal Medicine I. He had been taking 150 mg of dabigatran etexilate therapy twice daily before his admission (the length of dabigatran therapy was 50 days) for AF and continued with dabigatran etexilate therapy during the first days of his inhospital stay. He had a CHA2DS2-VASc score of 3 and no history of bleeding. Dabigatran was administered at 7:00 PM and 7:00 AM. Blood samples were taken 12 h after the previous drug administration (at 7:00 AM) for the assessment of the dabigatran trough level and 2 h after the next drug administration (at 9:00 AM) for the assessment of his dabigatran peak level. The patient was tested on the fifth day of his in-hospital stay, and had fasted before the blood sampling; dabigatran levels were assessed with Hemoclot® Thrombin Inhibitor Assay (Hyphen BioMed, Neuville-sur-Oise, France). The analysis of the dabigatran trough and peak levels demonstrated very low dabigatran levels (trough dabigatran level was 28 ng/ml, and peak dabigatran level was 55 ng/ml). With this knowledge, we decided to exchange dabigatran for apixaban. Apixaban therapy was started in a standard dose regiment of 5 mg twice daily. After 7 days of apixaban administration, repeated blood testing was performed: trough and peak samples were taken, the patient was fasting before the blood sampling, and anti-Xa activity analysis was performed with factor Xa-calibrated anti-Xa chromogenic analysis (the BIOPHEN® Heparin Assay and BIOPHEN® Apixaban Calibrator). Repeated analysis showed sufficient on-treatment anti-Xa apixaban activity in the trough and peak samples (trough apixaban anti-Xa activity was 142 ng/ml; and peak apixaban anti-Xa activity was 231 ng/ml). The ROTEM® analysis (INTEM® and EXTEM® reagent) on dabigatran etexilate and apixaban is reported in supplementary documents. In fact, there are only limited data regarding the optimal strategy for long-term oral anticoagulant therapy with NOAC in post-total gastrectomy patients with atrial fibrillation. Since the absorption of NOACs is mediated through the gastrointestinal tract, the bioavailability of NOACs could be reduced in post-total gastrectomy patients [6–9]. Recently, a preliminary study in post-bariatric surgery patients treated with NOACs showed that rivaroxaban plasma levels could be affected after bariatric surgery [10]. On the other hand, all apixaban-treated patients in this study had normal ontreatment apixaban plasma levels. This study enrolled only Electronic supplementary material The online version of this article (https://doi.org/10.1007/s00228-018-2571-9) contains supplementary material, which is available to authorized users.