Large numbers of Roux-en-Y gastric bypass (RYGB) surgery patients have psychiatric illnesses that are in part treated with medications preoperatively, but there are no objective data to guide psychiatric drug dosing postoperatively. An in vitro dissolution model was developed to approximate the gastrointestinal environment of the preoperative (control) and post-RYGB states. Medication tablets were placed in the two environments, and the median calculated weights of the dissolved portions were compared. Ten of 22 psychiatric medication preparations had significantly less dissolution and two had significantly greater dissolution in the post-RYGB environment, compared with the control environment. The results suggest a need for an in vivo study of serum drug levels after RYGB surgery in patients taking psychiatric medications. Differences in the pharmacokinetics of the postoperative RYGB patient may necessitate adjustments in dosing. (Psychosomatics 2005; 46:250-253) 

This has beend edited the following table to (a) make it easier to read, (b) to use brand names rather than generics, and (c) be reflective of the more commonly used meds. Please see the cited article, here, to view the table in its original form.

Please remember that this study used modeled environments. The study authors used crushed and immediate release formulas of these medications. PLEASE, remember, that extended release versions of psych meds behave totally differently, and really should not be used in a person with an RNY (this is being said by the author of the article~ not myself ~ PuggyDawn). Remember also, that you may not see the effects of decreased bioavailability for several weeks postop, as the half lives for some of these meds can be quite long. I encourage you to use this data to open a dialog with your psychiatric provider.

As you can see from the table, the amount of dissolved medication is higher in the preop environment for Prozac, Paxil, and Zoloft. Effexor and Celexa are pretty much the same for both environments. Wellbutrin, oddly enough, appears to have a higher amount of dissolved medication in the post-RYGB environment. The anti-anxiety/sedatives don’t have much difference between environments. The atypical antipsychotics, however, do show differences. Seroquel has the most difference between pre and post op (I can definitely speak to that—I’ve had to almost double my dose), with Geodon right behind. Risperdal and Zyprexa do show a difference as well. Lithium has increased amount of dissolved med in the post-op model, which makes me wonder about how ones lithium levels would be effected.

Please check out the article, cited here. Thanks to the author for allowing me to use it J

Table 1. Weights of Dissolved Portions of Psychiatric Medications in Standardized Dissolution Test Models of the Gastrointestinal Environments of Preoperative and Postoperative Roux-en-Y Gastric Bypass (RYGB) Patients.