Oral levothyroxine therapy postbariatric surgery: Biopharmaceutical aspects and clinical effects

Background: Bariatric surgery can lead to changes in the oral absorption of many drugs. Levothyroxine is a narrow therapeutic drug for hypothyroidism, a common condition among patients with obesity. Objective: The purpose of this work was to provide a mechanistic overview of levothyroxine absorption, and to thoroughly analyze the expected effects of bariatric surgery on oral levothyroxine therapy. Methods: We performed a systematic review of the relevant literature reporting the effects of bariatric surgery on oral levothyroxine absorption and postoperative thyroid function. A PubMed search for relevant keywords resulted in a total of 14 articles reporting levothyroxine status before versus after bariatric surgery. Results: Different mechanisms may support opposing trends as to levothyroxine dose adjustment postsurgery. On the one hand, based on impaired drug solubility/dissolution attributable to higher gastric pH as well as reduced gastric volume, compromised levothyroxine absorption is expected. On the other hand, the great weight loss, and altered set-point of thyroid hormone homeostasis with decreased thyroid-stimulating hormone after the surgery, may result in a decreased dose requirement. Conclusions: For patients after bariatric surgery, close monitoring of both the clinical presentation and plasma thyroid-stimulating hormone and T4 levels is strongly advised. Better understanding and awareness of the science presented in this article may help to avoid preventable complications and provide optimal patient care.