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Impact of gastric bypass surgery on the pharmacokinetics of oral contraceptive hormones

Anne Burke, Johns Hopkins University Bayview Medical Center, 2012

Project abstract

Background: The obesity epidemic continues to worsen. One of few successful treatments for obesity is bariatric surgery. About half of bariatric surgery patients are women of reproductive age. Gastric bypass, a common bariatric procedure, is associated with malabsorption of nutrients and medications. For that reason, the Centers for Disease Control advise against use of oral contraceptives (OC) after gastric bypass, despite a lack of clear guiding evidence. Since OC are still the most popular method of reversible contraception, and are often used by obese women for noncontraceptive benefits, there is need for better studies to evaluate OC use after gastric bypass.

Methods: We plan a prospective study to collect some of the first data in this area. We will enroll 16 women planning gastric bypass surgery, who have no contraindications to OC use. Women will take one 21-day cycle of OC in the months before their surgery, and one cycle 4 months after surgery. In this way, we can collect data on women as their own before-surgery controls. We will collect pharmacokinetic (PK) data for serum OC hormone levels, and correlate results with physiologic evidence of ovulation and contraceptive effect. We will compare standard PK parameters between groups. We hypothesize that malabsorption after gastric bypass will affect serum OC hormone levels, and subsequently, contraceptive efficacy, and that these effects will not be offset by any weight loss that may occur in the first few post-surgical months. We will also compare this prospectively collected data to historical data from a group of non-obese women in a study with similar methods. Thus, we can examine effects of weight and malabsorption.

Outcomes: This study will take approximately 18 months to complete; therefore, we request a 2-year funding cycle. Based on our anticipated results, we plan a more extensive, longer-term study of OC use after gastric bypass.

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