Savvy Psychopharmacology

How bariatric surgery affects psychotropic drug absorption

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Ms. B, age 60, presents to the clinic with high blood pressure, hyperlipidemia, type 2 diabetes mellitus, depression, and anxiety. Her blood pressure is 138/82 mm Hg and pulse is 70 beats per minute. Her body mass index (BMI) is 41, which indicates she is obese. She has always struggled with her weight and has tried diet and lifestyle modifications, as well as medications, for the past 5 years with no success. Her current medication regimen includes lisinopril 40 mg daily, amlodipine 5 mg daily, atorvastatin 40 mg daily, metformin 500 mg twice daily, dulaglutide 0.75 mg weekly, lithium 600 mg daily, venlafaxine extended-release (XR) 150 mg daily, and alprazolam 0.5 mg as needed up to twice daily. Due to Ms. B’s BMI and because she has ≥1 comorbid health condition, her primary care physician refers her to a gastro­enterologist to discuss gastric bypass surgery options.

Practice Points

Ms. B is scheduled for Roux-en-Y gastric bypass surgery. You need to determine if any changes should be made to her psycho­tropic medications after she undergoes this surgery.

There are multiple types of bariatric surgeries, including Roux-en-Y gastric bypass, sleeve gastrectomy, laparoscopic adjustable gastric band, and biliopancreatic diversion with duodenal switch (BPD/DS) (Figure1-4). These procedures all restrict the stomach’s capacity to hold food. In most cases, they also bypass areas of absorption in the intestine and cause increased secretion of hormones in the gut, including (but not limited to) peptide­-YY (PYY) and glucagon-like peptide 1 (GLP-1). These hormonal changes impact several factors, including satiety, hunger, and blood sugar levels.5

Types of bariatric surgeries

Roux-en-Y is commonly referred to as the gold standard of weight loss surgery. It divides the top of the stomach into a smaller stomach pouch that connects directly to the small intestine to facilitate smaller meals and alters the release of gut hormones. Additionally, a segment of the small intestine that normally absorbs nutrients and medications is completely bypassed. In contrast, the sleeve gastrectomy removes approximately 80% of the stomach, consequently reducing the amount of food that can be consumed. The greatest impact of the sleeve gastrectomy procedure appears to result from changes in gut hormones. The adjustable gastric band procedure works by placing a band around the upper portion of the stomach to create a small pouch above the band to satisfy hunger with a smaller amount of food. Lastly, BPD/DS is a procedure that creates a tubular stomach pouch and bypasses a large portion of the small intestine. Like the gastric bypass and sleeve gastrectomy, BPD/DS affects gut hormones impacting hunger, satiety, and blood sugar control.

How bariatric surgery can affect drug absorption

As illustrated in the Table,6-19 each type of bariatric surgery may impact drug absorption differently depending on the mechanism by which the stomach is restricted.

Drug absorption considerations for common bariatric surgeries

Drug malabsorption is a concern for clinicians with patients who have undergone bariatric surgery. There is limited research measuring changes in psychotropic exposure and outcomes following bariatric surgery. A 2009 literature review by Padwal et al7 found that one-third of the 26 studies evaluated provided evidence of decreased absorption following bariatric surgery in patients taking medications that had intrinsic poor absorption, high lipophilicity, and/or undergo enterohepatic recirculation. In a review that included a small study of patients taking selective serotonin reuptake inhibitors or venlafaxine, Godini et al8 demonstrated that although there was a notable decrease in drug absorption closely following the surgery, drug absorption recovered for some patients 1 month after Roux-en-Y surgery. These reviews suggest patients who have undergone any form of bariatric surgery must be observed closely because drug absorption may vary based on the individual, the medication administered, and the amount of time postprocedure.

Until more research becomes available, current evidence supports recommendations to assist patients who have a decreased ability to absorb medications after gastric bypass surgery by switching from an extended-release formulation to an immediate-release or solution formulation. This allows patients to rely less on gastric mixing and unpredictable changes in drug release from extended- or controlled-release formulations.

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