Use of Medicines and Predictions of Pharmacokinetic Changes after Bariatric Surgery

Danielle Wigg, University of Bath


A person living with obesity has a BMI of 30 or above, with Class I obesity being 30-35; Class II 35-40 and Class III 40 or more. Class II and III are hard to treat with diet and exercise alone and an operation to treat obesity (bariatric surgery) may be considered. There are several different types of operation, some which involve creating a small pouch out of the stomach and bypassing the first part of the small bowel. The reduced stomach size and subsequent changes in hormones that control appetite help weight loss, but are also thought to impact the amount of medicine in the bloodstream.

With all medicines, you need a certain level of drug in the bloodstream to obtain the desired effect. The recommended doses for commonly used medications are currently the same whether people are below or above average weight and whether they have surgery or not. Low medication blood levels can lead to treatment failing, too high and toxic effects can occur. Some people also do not use their medicines as prescribed. This may be due to concerns about the medicine, not understanding why they need it or practical problems. This may be particularly the case after bariatric surgery due to the many changes to regular medications that occur. We want to examine whether standard doses of commonly used medication lead to appropriate amounts of medication in the bloodstream and whether some patients would benefit from altered doses. The study will use a computer program to predict how common drugs behave after bariatric surgery, with the predictions tested in the real world by taking blood samples from patients before and after surgery. Challenges taking medication and what people know about their medication after surgery, will also be looked at, to tailor information to better meet patients’ needs.