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2014 ; 36
(6
): 716-23
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Effects of unbound mycophenolic acid on inosine monophosphate dehydrogenase
inhibition in pediatric kidney transplant patients
#MMPMID24739663
Smits TA
; Cox S
; Fukuda T
; Sherbotie JR
; Ward RM
; Goebel J
; Vinks AA
Ther Drug Monit
2014[Dec]; 36
(6
): 716-23
PMID24739663
show ga
BACKGROUND: Mycophenolic acid (MPA) is a key immunosuppressive drug that acts
through inhibition of inosine monophosphate dehydrogenase (IMPDH). MPA is
commonly measured, as part of therapeutic drug monitoring, as the total
concentration in plasma. However, it has been postulated that the free (unbound)
fraction of MPA (fMPA) is responsible for the immunosuppressive effects. In this
study, a sensitive low volume high-performance liquid chromatography (HPLC) assay
was developed to measure fMPA concentrations to explore the relationship between
fMPA and IMPDH activity. METHODS: To obtain fMPA concentrations, plasma samples
were filtrated using Centrifree ultrafiltration devices. The ultrafiltrate was
analyzed by HPLC using a Kinetex C18 column (2.6 ?m, 3.0 × 75 mm). fMPA
concentrations were compared with the total MPA concentrations available in 28
pediatric kidney transplant patients at 3 consecutive occasions after
transplantation. The relationship between fMPA and IMPDH activity was analyzed
using an Emax model. RESULTS: The HPLC assay, using 25 ?L of the ultrafiltrates,
was validated over a range from 2.5 to 1000 ?L with good accuracy, precision, and
reproducibility. Total and free MPA concentrations were well correlated (R =
0.85, P < 0.0001), although large intraindividual and interindividual variability
in the bound MPA fractions was observed. The overall relationship between fMPA
concentrations and IMPDH inhibition using the Emax model was comparable with that
of total MPA, as previously reported. The model estimated EC50 value (164.5 ?L)
is in good agreement with reported in vitro EC50 values. CONCLUSIONS: This study
provides a simple HPLC method for the measurement of fMPA and a pharmacologically
reasonable EC50 estimate. The good correlation between the total and free MPA
concentrations suggests that routine measurement of fMPA to characterize
mycophenolate pharmacokinetic and pharmacodynamic does not seem warranted,
although the large variability in the bound fractions of MPA warrants further
study.
|*Kidney Transplantation
[MESH]
|Child
[MESH]
|Chromatography, High Pressure Liquid/methods
[MESH]