Population pharmacokinetics of mycophenolic acid : a comparison between enteric-coated mycophenolate sodium and mycophenolate mofetil in renal transplant recipients.

OBJECTIVE: The pharmacokinetics of mycophenolic acid (MPA) were compared in renal transplant patients receiving either mycophenolate mofetil (MMF) or enteric-coated mycophenolate sodium (EC-MPS).
METHODS: MPA concentration-time profiles were included from EC-MPS- (n = 208) and MMF-treated (n = 184) patients 4-257 months after renal transplantation. Population pharmacokinetic analysis was performed using nonlinear mixed-effects modelling (NONMEM). A two-compartment model with first-order absorption and elimination was used to describe the data.
RESULTS: No differences were detected in MPA clearance, intercompartmental clearance, or the central or peripheral volume of distribution. Respective values and interindividual variability (IIV) were 16 L/h (39%), 22 L/h (78%), 40 L (100%) and 518 L (490%). EC-MPS was absorbed more slowly than MMF with respective absorption rate constant values of 3.0 h(-1) and 4.1 h(-1) (p < 0.001) [IIV 187%]. A mixture model was used for the change-point parameter lag-time (t(lag)) in order to describe IIV in this parameter adequately for EC-MPS. Following the morning dose of EC-MPS, the t(lag) values were 0.95, 1.88 and 4.83 h for 51%, 32% and 17% of the population (IIV 8%), respectively. The morning t(lag) following EC-MPS administration was significantly different from both the t(lag) following MMF administration (0.30 h; p < 0.001 [IIV 11%]) and the t(lag) following the evening dose of EC-MPS (9.04 h; p < 0.001 [IIV 40%]). Post hoc analysis showed that the t(lag) was longer and more variable following EC-MPS administration (morning median 2.0 h [0.9-5.5 h], evening median 8.9 h [5.4-12.3 h]) than following MMF administration (median 0.30 h [0.26-0.34 h]; p < 0.001). The morning MPA predose concentrations were higher and more variable following EC-MPS administration than following MMF administration, with respective values of 2.6 mg/L (0.4-24.4 mg/L) and 1.6 mg/L (0.2-7.6 mg/L). The correlation between predose concentrations and the area under the plasma concentration-time curve (AUC) was lower in EC-MPS-treated patients (r(2) = 0.02) than in MMF-treated patients (r(2) = 0.48).
CONCLUSION: Absorption of MPA was delayed and also slower following EC-MPS administration than following MMF administration. Furthermore, the t(lag) varied more in EC-MPS-treated patients. MPA predose concentrations were poorly correlated with the MPA AUC in both MMF- and EC-MPS-treated patients.