Influence of bariatric surgery on the use of some major drug classes

Introduction Patients undergoing bariatric surgery are severely obese and characterized by multidrug use for multiple comorbidities. Bariatric surgery can influence the prevalence and incidence of comorbidities, as well as the pharmacokinetics of drugs. This might lead to changes in the use of drugs. Aim To study the influence of bariatric surgery on the use of medication in patients before and after surgery, focusing on type and number of medications and daily dosage. Methods A retrospective and prospective observational study was carried out in Medical Centre Leeuwarden. After having obtained written informed consent drug dispensing data from pharmacies were collected from patients undergoing their first bariatric surgery between January 2008 and September 2011. Dispensing data from 6 months before until 12 months after surgery were analyzed. Drugs were classified according to the WHO-ATC classification system. Dosages of drugs were compared using defined daily dose (DDD). Results 450 patients were included (20.2% male). Mean age (SD) was 43.4 (10.1) yr; mean BMI (SD) was 44.9 (6.7) kg/m2. Roux-en-Y gastric bypass was performed in 74% of the patients. Mean BMI (SD) 12 months after surgery was 31.1 (5.6) kg/m2. The mean number of drugs per patient (95% CI) decreased from 3.66 (3.37-3.99) to 3.25 (3.04- 3.56). The mean number of drugs per patient decreased by 71%, 36%, 27%, 47%, 24% and 33% for antidiabetics, diuretics, beta blockers, agents acting on the reninangiotensin system, lipid modifying agents, and drugs for obstructed airway diseases respectively 12 months after surgery. From those drug classes patients used lower DDD 12 months after surgery. In contrast, a higher DDD was observed for thyroid hormone with no change in the mean number of drugs per patient. Conclusion Twelve months after bariatric surgery the use of drugs decreases in terms of mean number of drugs per patient and, for some major drug classes, in dose intensity. Dispensing data from pharmacies may provide detailed information on the use of medication by patients after bariatric surgery