Reply to letter: “What about drug bioavailability in patients who had bariatric surgery and dependent on immunosuppressives?”

Abstract

We appreciate the input of Drs Yildiz and Yildiz. 1 They suggest an addition to our review on the bioavailability of immunosuppressive drugs after bariatric surgery, 2 specifically in relation to transplantation surgery.It is indeed of high importance to highlight this topic as pretransplant bariatric surgery procedures probably will increase since this can help fulfilling weight criteria and get more patients eligible for transplantation. 3 The immunosuppressive drugs in question have narrow therapeutic windows, and certainly, there is a theoretical significant impact on their pharmacokinetics in patients subjected to bariatric surgery. The few existing case reports/studies on this topic have not been included in our study since they did not fulfil our inclusion criteria for this review, ie, longitudinal studies, investigating pharmacokinetic changes from before to after bariatric surgery. 4-7 Yemini et al did in fact investigate tacrolimus concentrations prior to and following bariatric surgery. However, since only trough concentrations were measured every 6 months, the findings from this study did not add to the mechanistic understanding of changes in bioavailability following surgery, which was the focus in our review. 8 The conclusion from our review makes extrapolation to a situation in which patients receive immunosuppressive drugs difficult. Hence, this topic should be highlighted in properly designed clinical trials in the future. With that said, regardless of bariatric surgery, dosing of tacrolimus varies from 1 to 30 mg/d between individuals, and hence, therapeutic drug monitoring (TDM) is mandatory for these patients and will probably deal adequately with the situation as long as bariatric surgery was performed before transplantation, but maybe not in the situation of surgery while on maintenance immunosuppressive therapy. Our general recommendation would therefore be to use standard TDM procedure in patients transplanted after bariatric surgery and to intensify TDM in case of bariatric surgery in transplanted patients.