Impact of mycophenolate mofetil loading on drug exposure in the early posttransplant period

Achieving adequate therapeutic levels of immunosuppressive medications is important in rejection prevention. This study examined exposure to mycophenolic acid (MPA) in kidney transplant patients within the first 5 days posttransplantation. Methods. This single-center, nonrandomized study of first solitary kidney allograft recipients receiving cyclosporine (n = 116) or tacrolimus (n = 50) included patients who received either 1 g or 1.5 g of mycophenolate mofetil twice daily starting postoperatively. Exposure to MPA was measured at days 3 and 5 posttransplant using published limited sampling time equations. Results. There were no significant differences in exposure in the cyclosporine-treated patients receiving 3-g (n = 22) compared to 2-g (n = 94) daily doses (AUC_[0-12] 33.8 ± 10.0 mg* (*)h/L versus 30.1 ± 9.7 mg*h/L, P = .20, respectively). About half the patients in both groups had AUC_[0-12] <30 mg*h/L on days 3 and 5 posttransplant. On the other hand, there was significantly greater exposure on day 3 in the tacrolimus-treated patients receiving 3 g (n = 21) compared to 2 g (n = 29) daily (AUC_[0-12] 43.1 ± 9.0 mg*h/L versus 36.8 ± 11.1 mg*h/L, P = .016, respectively). On day 3 one (4.8%) patient receiving 3 g had an AUC_[0-12] of <30 mg*h/L; whereas, eight (27.5%) receiving 2 g were below this level (P = .068). The AUC_[0-12] levels were not different on day 5. Conclusions. Loading with higher doses of mycophenolate mofetil results in greater exposure and a trend toward more patients in the therapeutic window within the first week for tacrolimus- but not for cyclosporine-treated patients.