Killing several birds with one stone: A multi-indication population pharmacokinetic model and Bayesian estimator for enteric-coated mycophenolate sodium

Aims: Mycophenolic acid (MPA), the active component of enteric-coated mycophenolate sodium (EC-MPS), exhibits highly variable pharmacokinetics. Only a few population pharmacokinetic (popPK) models and Bayesian estimators (MAP-BE) exist for estimating MPA AUC and all in renal transplantation. This study aimed to develop a popPK model and MAP-BE for MPA AUC estimation using a limited sampling strategy (LSS) in solid organ transplant (SOT), haematopoietic stem cell (HSC) recipients and patients with autoimmune diseases (AID) on EC-MPS.

Methods: Full and sparse MPA pharmacokinetic profiles were extracted from our ISBA system, split into development (75%) and validation (25%) sets. An additional extraction was performed after the modelling process for external validation. Pharmacokinetic parameters were estimated using Monolix® (SAEM algorithm). Several absorption models (first order, transit, gamma) were compared. AUC_predicted by MAP-BE and LSS was compared to the all-sample MAP-BE AUC_reference using Simulx®.

Results: We included 153 PK profiles (863 concentration) from 129 patients (116 SOT and HSC, 13 AID), median [min-max] age 45 years [6-80]. A one-compartment model with double-gamma absorption and first-order elimination best fitted the data. The final model included the EC-MPS indication and inter-occasion variability on gamma rate constants. Main PK parameters (mean ± SD) were Cl/F = 4.99 ± 2.22 L/h and Vd/F = 12.60 ± 0.08 L. The optimal LSS at 20 min, 2 h and 4 h post-dose showed good performance in both validation sets (rMPE -2.67% and -4.91%; RMSE 13.55% and 13.47%).

Conclusions: The double-gamma absorption model provided an accurate fit. The MAP-BE offers a tool for EC-MPS dose individualization in SOT, HSC and AID patients.