Quantification and 24-hour monitoring of mycophenolic acid by high-performance liquid chromatography in Japanese renal transplant recipients.

We developed a rapid, simple, and sensitive high-performance liquid chromatography method with UV detection for the quantitative determination of mycophenolic acid (MPA) in human plasma. MPA and the internal standard (naproxen) were separated using a mobile phase of 0.04 M H(3)PO(4)-acetonitrile-methanol (3:3:4 v/v/v) over a CAPCELL PAK C18 MG column. A flow-rate of 0.5 ml/min was used at ambient temperature and sample detection was carried out at 254 nm. The assay required only 100 microl of plasma and involved liquid-liquid extraction, which gave high recovery (>94%). The lower limit of quantification for MPA was 0.05 microg/ml. Inter- and intra-day coefficients of variation were less than 9.6% and accuracies were within 9.3%. Additionally, we validated this method in 24-hour monitoring of plasma MPA concentrations after mycophenolate mofetil (MMF) morning and evening administration in 40 Japanese renal transplant recipients with 1.5 g/day MMF. The time to reach the maximum (11.7 microg/ml) and second peak (4.5 microg/ml) of MPA after morning 0.75 g MMF administration was 2.6 h and 9.0 h, and time to reach maximum (10.5 microg/ml) after evening 0.75 g administration was 4.0 h.