Rivaroxaban use following bariatric surgery.

The recent case report by Dr. Mahlmann et al. [1] describing the pharmacokinetics of rivaroxaban in a bariatric surgery patient is a welcome addition to the literature. However, we feel it necessary to clarify the statement made regarding the ‘‘high bioavailability’’ of rivaroxaban and express caution regarding the use of this agent in postoperative bariatric surgery patients. The bioavailability of rivaroxaban depends on the dose and also the presence of food. Studies have shown that rivaroxaban doses up to 10 mg have high bioavailability. However, higher doses, which are employed for the prevention of stroke in atrial fibrillation and the treatment of venous thromboembolism (VTE), have poor bioavailability (*66 % for a 20 mg dose) [2, 3]. In pharmacokinetic studies, the bioavailability of higher doses is markedly improved (C80 %) when taken with food [2]. For this reason, the rivaroxaban prescribing information states that it should be taken ‘‘with food’’ for the atrial fibrillation and VTE treatment indications [4]. ‘‘With food’’ is a rather vague description with interpretations ranging from ‘‘take with a small snack’’ to ‘‘take with a full meal.’’ In the ROCKET–AF trial, patients were instructed to take their dose with their evening meal, but no specific calorie or size requirements were specified [5]. In the VTE treatment studies, patients were instructed to take their doses with meals with no further specifications [6, 7]. In the previously mentioned pharmacokinetic studies, ‘‘with food’’ was specifically a large meal of approximately 1,000 kcal [2]. While it is doubtful that subjects receiving rivaroxaban in clinical trials took their doses with such a large caloric intake, it seems reasonable to presume their doses were taken with standard meals and that their caloric intake was essentially normal (*1,800–2,500 kcal per day in the USA) [8]. Venous thromboembolism is a cause of morbidity and mortality after gastric bypass surgery and obesity increases the risk of atrial fibrillation [9, 10]. The relative ease of rivaroxaban compared to traditional agents may make it an attractive option for patients experiencing these events after bariatric surgery. To our knowledge, there are no clinical trial data to support the use of rivaroxaban for these indications specifically in bariatric surgery patients. Although the report by Mahlmann et al. [1] and a previous study that suggests that rivaroxaban is not influenced by extremes of weight [11] offers some reassurance, other factors must be considered before rivaroxaban is used in these patients. Specifically, we believe that patients who are in the early postoperative period after bariatric surgery should not receive rivaroxaban for either the atrial fibrillation or VTE treatment indications due to the low caloric intake (*500 calories per day) that is characteristic of the diets that these patients are placed on postoperatively [12]. In Dr. Mahlmann’s report [1], rivaroxaban was started several months after bariatric surgery and thus this patient’s caloric intake would likely have been much closer to normal relative to the postoperative period. Since the minimum amount of food required ensuring adequate absorption of rivaroxaban has not been determined, it is quite plausible that the low calorie consumption of the postoperative gastric bypass patient is insufficient to support adequate rivaroxaban absorption. Furthermore, Z. Thomas (&) Y. Bareket W. Bennett Hackensack University Medical Center, 30 Prospect Avenue, Hackensack, NJ 07601, USA e-mail: zthomas@rci.rutgers.edu