A simple HPLC method for monitoring mycophenolic acid and its glucuronidated metabolite in transplant recipients

Mycophenolic acid (MPA) is nowadays in broad clinical use as a substitute f or azathioprine. An immunoassay for MPA recently received approval for clin ical applications. The high performance liquid chromatography (HPLC) assay for measuring MPA and its glucuronide conjugate (MPAG) we describe here is not only rapid and simple but also extremely sensitive at plasma levels obt ained during standard immunosuppressive regimens. The determination of MPAG is possible without any change of the chromatographic conditions (detectio n wavelength of 214 nm, mobile phase: acetonitrile and 50 mmol/l o-phosphor ic acid (50:50, V/V), run time:15 min). The required equipment is a standar d HPLC system including a simple UV-detector. Sample volume of 400 mu l is required for both determinations. Detection limit is 0.25 mu mol/l for NIPA and 5 mu mol/l for MPAG. Linearity is excellent for serial dilutions (0.5- 25 mu mol/l for MPA, 25-500 mu mol/l for MPAG) and high accuracies favour t he method described. More than 2000 plasma samples tested for MPA in patients after heart transp lantation within one year and more than 500 samples for MPAG underline the clinical applicability of this assay.