*Purpose: Mycophenolate mofetil (MMF) is the most commonly prescribed immunosuppressant following transplantation in the United States. However, the occurrence of MMF therapy-related adverse events including diarrhea, leukopenia, rejection, and infection remains a challenge. There is conflicting data concerning the utility of monitoring mycophenolate exposure, especially regarding the relationship between dosing regimen and prediction of adverse events. Mycophenolate exposure was calculated using a three level abbreviated AUC approach (trough, half hour and two hours after administration). This study aims to determine if MMF exposure can be predicted by dosing regimens and understand if MMF exposure plays a role in managing or predicting the development of adverse events following renal transplantation.

*Methods: A search of the electronic medical record was used to identify patients meeting inclusion criteria: age 18 through 80, recipients of kidney or simultaneous kidney and pancreas transplant at ECMC between January 2013 and December 2016, and received MMF with at least one level. Data collection included recipient demographics, type of primary renal disease, type of donor, and recipient factors including: time since transplant, number of previous transplants, MMF regimen and frequency of changes, MMF levels, laboratory values (serum creatinine, creatinine clearance, leukocytes, lymphocytes), presence of BK virus or CMV disease, induction therapy, concurrent suppressant regimen and levels, and presence of biopsy proven acute rejection (BPAR). The exposure of the patient to MMF was calculated using the area under the concentration-time curve (AUC). The MMF regimen was then compared with the levels obtained (trough, C1 and C2, and AUC) and analyzed as it relates to a composite endpoint of adverse events.

*Results: This study did not demonstrate a statistically significant relationship between MMF exposure and incidence of leukopenia, CMV disease, BK virus, or BPAR. BPAR and infection (CMV disease or BK virus) were associated with lower MMF total daily doses. As expected, a lower MMF total daily dose was associated with a sub-therapeutic AUC, whereas a higher dosage was associated with supra-therapeutic AUC. The mean MMF total daily dose was 1103mg, 1399mg, and 1577mg for sub-therapeutic, therapeutic, and supra-therapeutic exposure, respectively. However, an appropriate dosage adjustment in response to AUC occurred only 20.7% of the time for sub-therapeutic levels and 42.3% for supra-therapeutic levels.

*Conclusions: There is no demonstrated benefit in obtaining MMF exposure (AUC) in renal transplant recipients as it does not predict incidence of adverse events. Additionally, providers were hesitant to adjust the MMF dose for sub-therapeutic or supra-therapeutic levels.

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