Transforming treatment: the impact of bariatric surgery on oral drug absorption

Obesity represents a significant threat to global public health, with an estimated 16% of adults worldwide (2022) being classified as people with obesity, with a body mass index of 30 or more. Bariatric surgery is regarded as the most effective treatment option for people with obesity, with the three main types of bariatric surgery being gastric bypass or Roux-en-Y gastric bypass, laparoscopic gastric band and laparoscopic sleeve gastrectomy. Drug bioavailability after oral administration is affected by several factors including properties of the drug itself, formulation properties and anatomical and physiological factors. Procedures such as gastric bypass and laparoscopic sleeve gastrectomy result in significant anatomical and physiological alterations thought to profoundly influence oral drug bioavailability post-operatively. Consequently, following bariatric surgery there is a risk of sub-therapeutic drug levels leading to treatment failure, or the risk of potential toxicity if levels are elevated. In this review, previously unexamined aspects such as the impact of the “Very Low-Calorie Diet” (VLCD) initiated prior to surgery on anatomical parameters and subsequent pharmacokinetic changes, are explored. This review also highlights alterations in hepatic and renal volume that are expected to have a significant impact on renal and hepatic clearance. A clearer understanding of the effect of physiological alterations and weight loss on drug performance post-surgery would support more evidence-based medicines optimisation in this frequently complex patient group.