In the case of the majority of studied drugs , an increased absorption rate was observed early after RYGBP .
The effect on systemic exposure allows for a low degree of extrapolation , including between drugs subjected to the same major metabolic and transporter pathways .
Anatomical changes in the gastrointestinal tract and subsequent weight loss may influence drug disposition and thus drug dosing following bariatric surgery .
This review systematic ally examines the effects of bariatric surgery on drug pharmacokinetics , focusing especially on the mechanisms involved in restricting oral bioavailability .
Comparison of Bioavailability of Single‐Dose Extended‐Release Venlafaxine Capsules in Obese Patients Before and After Gastric Bypass Surgery
STUDY OBJECTIVE The extended-release ( ER ) form of venlafaxine is preferred because of improved patient adherence , but the immediate-release ( IR ) form is frequently used after Roux-en-Y gastric bypass ( RYGB ) surgery because of concerns for malabsorption . The objective of this study was to determine whether a statistically significant and predictable change in the bioavailability of venlafaxine ER  capsules occurs after RYGB . DESIGN Prospect i ve nonblinded single-dose pharmacokinetic study . SETTING Clinical research unit at a large tertiary care medical practice . PATIENTS Ten adult pre-bariatric surgery patients who met the criteria for noncomplicated RYGB were enrolled and served as their own controls . INTERVENTIONS Patients were administered one venlafaxine ER 75-mg capsule at two visits-the first visit at least 1 week before undergoing RYGB and the second visit 3 - 4 months after RYGB . Blood sample s were collected at predetermined intervals over 48 hours after each dose , and the pharmacokinetics of venlafaxine  were measured . MEASUREMENTS AND MAIN RESULTS Plasma levels of venlafaxine and its primary metabolite , O-desmethylvenlafaxine ( ODV ) , were compared at baseline and 3 - 4 months after RYGB . The areas under the serum concentration-time curves from 0 - 24 hours ( AUC0 - 24 ) for venlafaxine ( mean ± SD 734 ± 602 vs 630 ± 553 ng·hr/ml , p=0.22 ) and ODV ( mean ± SD 894 ± 899 vs 1083 ± 972 ng·hr/ml , p=0.07 ) were similar before and after RYGB . Using a bioequivalence approach , differences in pre-RYGB and post-RYGB values of AUC0 - 24 , peak serum concentration , and time to peak serum concentration were not statistically significant for either venlafaxine or ODV . CONCLUSION This study suggests that RYGB does not significantly alter the amount of venlafaxine or its active metabolite , ODV , absorbed from a venlafaxine ER capsule or the time over which it is absorbed
In the case of the majority of studied drugs , an increased absorption rate was observed early after RYGBP .
The effect on systemic exposure allows for a low degree of extrapolation , including between drugs subjected to the same major metabolic and transporter pathways .
Anatomical changes in the gastrointestinal tract and subsequent weight loss may influence drug disposition and thus drug dosing following bariatric surgery .
This review systematic ally examines the effects of bariatric surgery on drug pharmacokinetics , focusing especially on the mechanisms involved in restricting oral bioavailability .