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21 Medicines management after bariatric surgery

Objectives The number of hospital admissions for weight loss surgery has increased two to three-fold in the 10 years to 2015 (Australian Institute of Health and Welfare) and consequently general practitioners (GPs) will be managing more patients post bariatric surgery. Bariatric surgery can significantly impact the absorption and metabolism of medicines resulting in changes in efficacy and adverse effects. Despite the number of bariatric surgeries performed, these changes remain poorly documented and understood. Patients undergoing bariatric surgery often have co-morbidities requiring multiple medicines and pharmacotherapy may be complicated not only by changes in absorption and metabolism following surgery, but also by improvement in conditions such as chronic pain, diabetes and hypertension, after surgery. Patients invariably require modifications to their medicines. Individualisation and lifestyle advice, guarding against subsequent medicalisation of their life situation, is an important part of ensuring the most appropriate therapeutic strategy in an area where there is limited evidence. Method A team of experienced clinical pharmacists from the Drug and Therapeutics Information Service (DATIS), who provide a therapeutic and decision support service to general practitioners (GPs), received a number of queries around medicine management in patients who had undergone bariatric surgery. An evidence-based literature review was conducted and a DATIS publication ‘Medicines after bariatric surgery’ was prepared, reviewed by local experts (Feb 2019) and circulated to interested GPs. To highlight our findings, we describe the management, after bariatric surgery, of a patient with chronic pain and diabetes. Results Through the application of pharmacokinetics and the published evidence to date, a case is presented highlighting dosing implications for some common medicines, such as proton pump inhibitors (PPIs), opioids, metformin, SGLT2 inhibitors, antihypertensives and selective serotonin re-uptake inhibitors (SSRIs), in a patient with chronic pain and diabetes who has undergone bariatric surgery. Conclusions The management of patients post bariatric surgery is a growing area in which GPs will be increasingly required to have some knowledge and practical skill. Bariatric surgery may alter the absorption, distribution, metabolism or elimination of orally administered drugs via changes to the gastrointestinal tract anatomy, body weight and adipose tissue composition. Research is limited and there are large inter- and intra-individual variations. Doses of medications for many chronic conditions (e.g. chronic pain, diabetes, hypertension and dyslipidaemia) may need to be adjusted as weight loss occurs. This case study presentation demonstrates how GPs can ensure appropriate management of patients after bariatric surgery to avoid medicalising a life experience and to minimise the perception of disability, in an area where there is emerging evidence.