Population pharmacokinetics of mycophenolic acid in children and young people undergoing blood or marrow and solid organ transplantation
Authors: Zeng Lihua , Blair Elaine Y. L. , Nath Christa E. , Shaw Peter J. , Earl John W. , Stephen Katherine , Montgomery Kay , Coakley John C. , Hodson Elisabeth , Stormon Michael , McLachlan Andrew J. 
Published: June 2010

WHAT IS ALREADY KNOWN ABOUT THIS PROJECT?

• Mycophenolate mofetil (MMF) is an immunosuppressant drug used for the treatment and prevention of graft vs. host disease in blood or marrow transplantation and acute graft rejection in solid organ transplantation.

• Mycophenolic acid (MPA) pharmacokinetics have not been thoroughly studied in paediatric blood or marrow transplant recipients and guidance for optimal dosing of mycophenolic acid in children is lacking.

• Mycophenolic acid exhibits considerable inter‐ and intra‐patient pharmacokinetic variability in adults and paediatric transplant recipients.

• The AUC of mycophenolic acid over a 12 h dose interval at steady‐state is generally agreed to be the most reliable metric associated with the risk of acute rejection.

• Population pharmacokinetic analysis can utilize concentration information from both intensive sampling and sparse sampling to provide pharmacokinetic parameter estimates, estimates of inter‐ individual and intra‐individual variability in these parameters and allows patient characteristics explaining inter‐individual variability to be quantified.

WHAT THIS STUDY ADDS

• This study is one of the first investigations in which a population pharmacokinetic modelling approach was applied to assess the pharmacokinetics of both intravenous and oral MMF in children and young people undergoing blood or marrow and solid organ transplantation.

• Bodyweight and concomitant ciclosporin were found to influence MPA pharmacokinetics.

• This study evaluated current dosing strategies and found that they may be suboptimal for children weighing less than 10 kg.

AIMS

To characterize the population pharmacokinetics of mycophenolic acid (MPA) and evaluate dose regimens using a simulation approach and accepted therapeutic drug monitoring targets in children and young people undergoing blood or marrow, kidney and liver transplantation.

METHODS

MPA concentration–time data were collected using an age specific sampling protocol over 12 h. Some patients provided randomly timed but accurately recorded blood samples. Total and unbound MPA were measured by HPLC. NONMEM was employed to analyze MPA pharmacokinetic data. Simulations (n= 1000) were conducted to assess the suitability of the MPA dose regimens to maintain total MPA AUC(0,12 h) within the range 30 and 60 mg l−1 h associated with optimal outcome.

RESULTS

A two‐compartment pharmacokinetic model with first‐order elimination best described MPA concentration–time data. Population mean estimates of MPA clearance, inter‐compartmental clearance, volumes of distribution in the central and peripheral compartments, absorption rate constant and bioavailability were 6.42 l h−1, 3.74 l h−1, 7.24 l, 16.8 l, 0.39 h−1 and 0.48, respectively. Inclusion of bodyweight and concomitant ciclosporin reduced the inter‐individual variability in CL from 54.3% to 31.6%. Children with a bodyweight of 10 kg receiving standard MPA dose regimens achieve an MPA AUC below the target range suggesting they may be at a greater risk of acute rejection.

CONCLUSIONS

The population pharmacokinetic model for MPA can be used to explore dosing guidelines for safe and effective immunotherapy in children and young people undergoing transplantation.