Lithium Toxicity Following Roux-en-Y Gastric Bypass

Address correspondence to: Kate Walsh, RPh, BScPhm, HBSc, Pharmacy Services, Women's College Hospital, 76 Grenville Street, Toronto, Ontario, M5S 1B1, Canada, E-mail: [email protected]

Introduction

Patients undergoing weight loss surgery often have comorbid psychiatric illness. The Wilford Hall Medical Center found that 34% of patients undergoing routine preoperative psychiatric consultation were taking psychiatric medications.¹ Unfortunately, there is little evidence to guide the management of these medications in the perioperative and extended postsurgical period.

In Roux-en-Y gastric bypass (RYGB), weight loss is achieved through restriction (due to the construction of a smaller gastric pouch) and malabsorption (due to changes to the stomach and intestinal anatomy).² Lithium is absorbed rapidly and completely by the gastrointestinal tract.³ These postsurgical changes may impact the absorption of many medications, but this is particularly concerning for agents with a narrow therapeutic window such as lithium (0.8-1.2 mEq/L or mmol/L for acute treatment and 0.6-1.0 mEq/L or mmol/L for maintenance).^2,3 Furthermore, the pre-RYGB liquid meal replacement diet required to shrink the liver alters fluid and sodium intake, both of which can influence lithium levels.²

Seaman et al. designed an experimental media to mimic the gastrointestinal tract of a post-RYGB patient and a preoperative comparison patient. They tested the dissolution fractions of 22 common psychiatric immediate release medications. Lithium carbonate dissolved significantly more in the post-RYGB model, which suggests that careful monitoring and perhaps dose reductions may be necessary for patients after surgery.¹

Postoperative dietary recommendations are clear liquids for 1-2 days then a full liquid diet for 1-2 weeks then pureed/soft foods for 1-2 weeks.⁴ Short-term diet-related complications include nausea and vomiting, intolerance to the reintroduction of specific foods, and dumping syndrome, which is characterized by lightheadedness, palpitations, sweating, and diarrhea in response to consumption of high fat and/or sugar foods. Dehydration is also common due to decreased oral intake, since patients are unable to consume large amounts of liquids at one time, and drinking fluids with food is not permitted.⁴ These complications may lead to renal impairment, which significantly increases the risk of lithium toxicity.² Signs and symptoms of lithium toxicity include...