The reduced function allele SLCO1B1 c.521T>C is of no practical relevance for the renal graft function over the first post-transplant year in patients treated with mycophenolic acid

Objective It is unclear whether renal transplant recipients treated with mycophenolic acid (MPA) who carry the reduced-function allele at polymorphism SLCO1B1 c.521T>C differ from their wild-type peers regarding renal outcomes and tolerability. We aimed to estimate the effect of this polymorphism on the graft function (estimated glomerular filtration rate, eGFR) over the first 12 post-transplant months in patients on MPA-based maintenance immunosuppression. Methods In a 12-month observational cohort study, consecutive adult patients were repeatedly assessed for eGFR. The SLCO1B1 c.521C>T variant allele carriers (exposed) and wild-type subjects (controls) were balanced on a range of demographic, medical, and genetic variables at baseline, and eGFR trajectory was estimated with further adjustment for time-varying covariates. A subset of patients were assessed for exposure to MPA 5–7 days after the transplantation. Results The adjusted eGFR slopes from day 1 to day 28 (daily), and from day 28 to day 365 (monthly) were practically identical in exposed ( n = 86) and control ( n = 168) patients [geometric means ratios (GMR) = 0.99, 95% confidence interval (CI) = 0.92–1.06 and GMR = 0.98, 0.94–1.01, respectively]. The rates of adverse renal outcomes and possible MPA-related adverse effects were low, and similar in exposed and controls [rate ratios (RR) = 0.94, 0.49–1.84 and RR = 1.08, 0.74–1.58, respectively]. The pharmacokinetic analysis did not signal meaningful differences regarding exposure to MPA, overall (exposed n = 23, control n = 45), if cotreated with cyclosporine ( n = 17 vs. n = 26) or with tacrolimus ( n = 8 vs. n = 17). Conclusions In patients treated with MPA, variant allele SLCO1B1 c.521T>C appears of no practical relevance regarding the 12-month renal graft function, MPA safety and exposure to MPA at early steady-state.