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Tacrolimus concentration to dose ratio in solid organ transplant patients treated with FMT for RCDI

Fecal microbiota transplantation (FMT) is increasingly being performed for Clostridium difficile infection in solid organ transplant patients; however, little is known about the potential pharmacokinetic or pharmacomicrobial effects this may have on tacrolimus levels. We reviewed the medical records of 10 solid organ transplant patients from September 2012 – December 2016 who were taking tacrolimus at time of FMT for recurrent C. difficile infection. We compared the differences in tacrolimus concentration / dose ratio (C/D ratio) three months prior to FMT vs three months after FMT. The mean of the differences in C/D ratio calculated as ng/mL / mg/kg/day was -17.65 (95% CI -1.25 – 0.58) ng/mL / mg/kg/day, p-value 0.43 by Wilcoxon signed-rank test. The mean of the differences in C/D ratio calculated as ng/mL / mg/day was -0.33 (95% CI -1.25 – 0.58) ng/mL / mg/day, p-value 0.28 by Wilcoxon signed-rank test. Of these patients, 2/10 underwent allograft biopsy for allograft dysfunction in the year after FMT, with no evidence of allograft rejection on pathology. These preliminary data suggest that FMT may not predictably alter tacrolimus levels and support its safety for solid organ transplant patients however further study in randomized trials is needed.


Fecal microbiota transplantation (FMT) is a highly effective treatment for recurrent Clostridium difficile infection (RCDI), but its pharmacologic effects are poorly understood. Solid organ transplant (SOT) recipients are typically prescribed a cocktail of immunomodulatory medications to prevent allograft rejection but become toxic when given in excessive amounts. Tacrolimus is an immunosuppressive drug that reduces the activity of the immune system to reduce the risk of organ rejection. Many factors are known to influence tacrolimus concentration/dosing ratio. This study aimed to evaluate if FMT is one such factor, by comparing tacrolimus dosing in the three months previous to FMT and the three months following FMT.

Ten patients qualified and were approved for this study. All underwent FMT at Emory University from July 1st, 2012 to December 21st, 2016. All patients included in this study had two or more episodes of frequent, watery diarrhea with positive lab testing for C. diff. Concentration/ dose ratio pf tacrolimus was taken from the medical record of patients three months prior to first FMT and compared to three months after first FMT.

Of the ten patients included in the study, four received multiple FMT’s before diarrhea was resolved. The patients that received multiple FMTs had generally complicated solid-organ transplant courses with multiple complications. From the data collected, there was no significant difference in tacrolimus total daily dose or concentration/ dose ratio at three months after FMT compared to three months prior to FMT. This data suggests that FMT may not predictably alter tacrolimus levels but supports the safety of FMT for solid organ transplant patients. Further research is needed of potential immunomodulatory and pharmacomicrobial effects in SOT.


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