Background: Data on the absorption of orally administered drugs following Roux-en-Y gastric bypass (RYGB) surgery in obese patients are limited and inconclusive. As it is difficult to predict changes in absorption, studies on frequently used drugs in this population are necessary. Acetylsalicylic acid (ASA) and omeprazole are two commonly prescribed drugs in obese patients.
Methods: In this repeated measures study, omeprazole and salicylic acid (SA) serum concentrations were measured before and after RYGB in 34 morbidly obese subjects. Time to maximum concentration (Tmax), lag time (Tlag), maximum concentration (Cmax), and area under the serum concentration versus time curve (AUC) were calculated for both drugs to determine possible differences in drug absorption after the procedure.
Results: For SA, Tmax significantly decreased after RYGB, while both Cmax and AUC0–24 significantly increased. For omeprazole, both Tmax and Tlag significantly decreased after RYGB, while Cmax significantly increased. Mean AUC0–12 significantly decreased post-surgery. The difference in AUC0–12 before and after surgery varied between subjects.
Conclusions: Our study shows a faster absorption of both ASA and omeprazole after RYGB. The exposure to ASA is higher post-surgery, but the standard dose of 80 mg does not need to be modified, considering its range in effective dose. The exposure to omeprazole is, on average, decreased after surgery. Clinicians should be aware to increase the dose of omeprazole if symptoms suggest inadequate response.

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Obesity Surgery
Department of Clinical Chemistry

Mitrov-Winkelmolen, L., van Buul-Gast, M.-C. W., Swank, D., Overdiek, H. W. P. M., van Schaik, R., & Touw, D. (2016). The Effect of Roux-en-Y Gastric Bypass Surgery in Morbidly Obese Patients on Pharmacokinetics of (Acetyl)Salicylic Acid and Omeprazole. Obesity Surgery, 26(9), 2051–2058. doi:10.1007/s11695-016-2065-8