Schaier M, Scharpf D, Scholl C, et al.
Pharmacodynamic Drug Monitoring a New Tool for Individualised
Immunosuppression in Patients with ANCA-Associated Systemic
Vasculitis.
ASN Annual Meeting -- San Diego
J Am Soc Nephrol
(Nov) 20:410A 2009

Background: Mycophenolic acid (MPA) exerts its immunosuppression by
inhibiting inosine 5'-monophosphate dehydrogenase (IMPDH), depleting
activated lymphocytes of guanine nucleotides and retarding their
proliferation. MPA plays an increasing role in the maintenance therapy of
ANCA- associated systemic vasculitis (AASV).
Objectives: The purpose
of our study was to examine the correlation between clinical outcome and
pharmacokinetic- pharmacodynamic relationships of MPA in patients with
AASV.
Methods: We studied 27 Caucasian patients with stable AASV under
maintenance therapy with MPA. MPA and IMPDH concentrations were measured by a
validated high performance liquid chromatography method in 12 plasma samples
collected at predose and at 0.5, 1, 1.5, 2, 3, 4, 5, 6, 8, 10 and
12h.
Results: Patients were followed for a mean (+/-SD) period of 14+/
-6 months. During observation period, no patient had a relapse, but three
AASV patients showed a higher disease activity, with elevated BVAS. Patients
with increased disease activity had significant higher levels of mean (+/-
SD) IMPDH AEC (0-12) 91+/-20 nmol*h/mg protein/h, indicating inadequate IMPDH
suppression. Stable patients had markedly lower IMPDH AEC (0-12) 57+/-23
nmol*h/mg protein/h (p=0.02). Maximum IMPDH concentration was significantly
higher in patients with increased disease activity (p=0.02) in comparison to
stable patients. Stable patients showed slightly higher MPA AUC (0-12) (70+/-
40 mg*h/L) in comparison to patients with increased BVAS (59+/-21 mg*h/L).The
difference failed statistical significance (p=0.66). Furthermore, there was
no statistical correlation between MPA AUC (0-12) and IMPDH AEC (0-12). The
relative risk for increased disease activity is 6.6 time higher for patients
with IMPDH AEC (0-12) > 60 nmol*h/mg protein/h and MPA AUC (0-12) < 68
mg*h/L.
Conclusion: Pharmacodynamic drug monitoring seems to be a new
tool to detect inadequate immunosuppression in AASV patients.

© Copyright 2009-2010 American Society of
Nephrology.Reproduced with permission.
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