Weighing In on the Recommendations for Oral Anticoagulant Use Following Bariatric Surgery

Obesity continues to present a serious public health challenge, especially as it is associated with an increased risk of the development and progression of several weight-related comorbidities, including hypertension, diabetes, coronary artery disease, hyperlipidemia, obstructive sleep apnea, atrial fibrillation, and venous thromboembolism.¹ The increased risk of atrial fibrillation and venous thromboembolism in this population prompts the need to consider oral anticoagulation.^1,2 This is further complicated by the fact that bariatric surgery has become increasingly more common as an effective approach to reducing weight and decreasing the risk of obesity-associated comorbidities.^1,2

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It is estimated that in the United States, approximately 200,000 bariatric surgeries are performed each year.² As a result of bariatric surgery, the pharmacokinetics of many medications are altered, which thereby has implications on their overall safety and efficacy.³ Understanding the considerations that should be made and the current recommendations around oral anticoagulant use following bariatric surgery is crucial for this growing patient population.

The 3 most common types of bariatric surgery are gastric banding, sleeve gastrectomy, and Roux-en-Y gastric bypass surgery.^2,3 The gastric banding procedure places a band around the stomach, which works to reduce its volume, thereby limiting caloric intake. A sleeve gastrectomy removes a portion of the stomach, which reduces its volume and limits caloric intake. Finally, a Roux-en-Y gastric bypass surgery involves the stapling of the stomach into a smaller pouch that is then connected to the jejunum. This, in turn, results in bypassing the majority of the stomach and the proximal small intestine. Depending on the bariatric surgery conducted, there are implications on a medication’s efficacy, depending on its pharmacokinetics and where along the gastrointestinal tract it is primarily absorbed.³ Another important consideration is whether or not food is necessary for optimal absorption.³

Anatomical alterations result in many downstream changes, as well, such as changes in pH, gastric volume, food intake, surface area for absorption, gastric emptying and transit times, and intestinal enzymes and efflux pumps among others.³ Therefore, it is important to consider how bariatric surgery affects the pharmacokinetics of the various oral anticoagulants in order to determine safety and efficacy. Table 1^1,2,3 below highlights the important characteristics of the oral anticoagulants that need to be considered, especially if they are to be used post-bariatric surgery. Table 2^1-4 highlights the expected impact that each of the 3 bariatric surgeries will have on the individual direct oral anticoagulants (DOACs).

Table 1. Characteristics of oral anticoagulants

P-gp: P-glycoprotein

Table 2. The expected impact of bariatric surgeries on the absorption of direct oral anticoagulants (DOACs)

The available literature suggests that warfarin dosing needs will be reduced during the first 3 to 4 weeks following bariatric surgery.² However, after this initial period, the warfarin dosing needs will once again increase and eventually return to near normal requirements. The reason as to why there is this initial need for decreased warfarin requirements remains unclear. It is thought that the caloric reduction alone post-bariatric surgery could be contributing to a vitamin K deficiency as well as the altered vitamin K absorption due to anatomical changes, which normally occurs in the proximal small intestine and requires the presence of bile salts.²

With all of this in mind, the recommendation is that warfarin be used for patients who have undergone bariatric surgery and require oral anticoagulation.^1-3 Warfarin dosing can be monitored much more closely through the use of the international normalized ratio, and the dose can be adjusted accordingly. However, if a DOAC is to be used following bariatric surgery, the recommendation is that drug-specific peak and trough levels be monitored.

The challenge with the DOACs is that the lab tests are not widely available at all institutions and locations, and there are no clearly defined therapeutic ranges for each at this time.⁴ Pharmacists can play an important role in the selection and management of DOAC therapy for patients who have undergone bariatric surgery, providing their expertise and knowledge to the wider care team.

References

1. Nasser MH, Jabri A, Gandhi S, et al. Oral anticoagulant use in morbid obesity and post bariatric surgery: a review. The American Journal of Medicine. 2021;134:1465-1475.

2. Martin KA, Lee CR, Farrell TM, et al. Oral anticoagulant use after bariatric surgery: a literature review and clinical guidance. The American Journal of Medicine. 2017; 130:517-524.

3. Miedziaszczyk M, Ciabach P, Szalek E. The effects of bariatric surgery and gastrectomy on the absorption of drugs, vitamins, and mineral elements. Pharmaceuticals. 2021; 13:1-19.

4. Leong R, Chu DK, Crowther MA, et al. Direct oral anticoagulants after bariatric surgery – What is the evidence? J Thromb Haemost. 2022; 20:1988-2000.