Pharmacokinetic effects of bariatric surgery.

Allan Edwards, Mary H H Ensom

Faculty of Pharmaceutical Sciences, The University of British Columbia, Vancouver, BC, Canada.

The Annals of pharmacotherapy 2012 Jan

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To evaluate the effect of bariatric surgery on the pharmacokinetics of medications. EMBASE (1980-September 2011), PubMed (1947-September 2011), MEDLINE (1948-September 2011), and International Pharmaceutical Abstracts (1970-September 2011) were searched for the following terms: gastric bypass or stomach bypass or bariatric surgery, and pharmacokinetic. All English-language primary literature that reported pharmacokinetic parameters for orally dosed medications in post-bariatric surgery patients was evaluated, with the exception of studies involving the jejunoileal bypass method. Worldwide, the incidence of obesity is increasing and so are options for managing it, including bariatric surgery. Major alterations to the physical structure of the gastrointestinal tract may cause changes in pharmacokinetic parameters of oral medications, which theoretically could lead to increased or decreased drug exposure. We reviewed 11 prospective trials, 5 of which were available only as abstracts and all of which were small with relatively low power (n = 6-36). The studies were split almost equally between using subjects as their own controls or using separate control subjects; 1 study used historical data as the control. Results were varied, highlighting the multifactorial nature of pharmacokinetics. Drugs such as atorvastatin, which undergo presystemic intestinal metabolism via CYP3A, may show increased bioavailability, whereas those such as amoxicillin, which rely on transport mediators, may be decreased. Most of the studies lacked sufficient power to show significant changes in post-bariatric surgery patients. Bariatric surgical procedures may result in altered pharmacokinetic parameters, but the literature is lacking in sufficient quantity and quality of studies to make solid conclusions and recommendations. Until more studies of sufficient power are completed, clinicians should closely monitor these patients in the immediate and distant postsurgical period for signs of both drug efficacy and toxicity and adjust their medications as required.