The UKCPA explains the effects of bariatric surgery

Both the reduced gastric volume and changed gastrointestinal anatomy following weight loss surgery have profound effects on a patient’s ability to tolerate medication and on the pharmacokinetics of medicines. Hormonal changes following the surgery also often necessitate review of treatment regimens.

Both NICE guidelines and the weight loss surgeons’ own interest group’s standards recommend that bariatric surgery only takes place in a specialist bariatric unit within a set pathway and with provision of a tight follow-up package, which explicitly includes a medication review – yet hospitals are always looking to discharge patients as fast as possible.

Preliminary research suggests that some patients have difficulty taking their prescribed drug therapy following weight loss surgery but do not know who to ask for advice. The anatomical and physiological changes from bariatric surgery are life-long and may have an effect on the pharmacokinetics of any medication started. To date there is only limited evidence available on the exact effects different bariatric surgery has on particular drugs’ pharmacology.

Scenario

Ms L, a former regular customer, comes into the pharmacy. She enthusiastically tells you about the gastric bypass surgery she had three years ago and the positive changes the surgery and associated interventions brought.

She has managed to maintain her weight loss and is more active, has a new partner with whom she is thinking of starting a family, and has managed to come off all her medication during the past year, having previously been on antidiabetic, antihypertensive and analgesic medicines. However, recently she has been feeling quite tired and suffered from repeated nose bleeds. What may be the cause of these symptoms?

A: One commonly performed procedure to achieve lasting weight loss is the Roux-en-Y gastric bypass. This leads to a malabsorptive state, the extent of which depends on the type of bypass performed. Along with all her other medication, Ms L may have stopped her water and fat soluble vitamins and minerals, which she requires life-long. Deficiency of iron, folic acid or vitamin B12 could all lead to anaemia and associated tiredness; vitamin K deficiency to bleeding.

Ms L should urgently be restarted on suitable supplements and be investigated for nutritional deficiencies. Gastric bypass may also lead to reduced absorption of oral contraceptives, while weight loss following surgery can improve fertility. Ms L needs to be made aware of this as her tiredness could be a sign of early pregnancy – in which case resuming folic acid and vitamin D supplements would be even more important, as well as referral to specialist dietetic advice.