Comparison of high-performance liquid chromatography and enzyme-multiplied immunoassay technique to monitor mycophenolic acid in paediatric renal recipients

Therapeutic drug monitoring (TDM) of mycophenolate mofetil (MMF) is recommended to guide immunosuppression. High-performance liquid chromatography with ultraviolet (HPLC-UV) or the enzyme-multiplied immunoassay technique (EMIT), used to measure mycophenolic acid (MPA) were compared in an exclusive paediatric renal transplant population. Twenty patients were included as part of the pharmacokinetics study of MMF, and 88 additional samples were drawn for TDM. Agreement between HPLC-UV and EMIT was assessed by the Bland–Altman method. With the two methods, pre-dose concentrations were not normally distributed. After logarithmic transformation, their mean was 0.79 ± 1.16 μg ml −1 and their mean difference was 0.34 ± 0.16 μg ml −1 [95% confidence interval (95%CI 0.30–0.38 μg ml −1 , with antilogarithmic values of these limits of 1.34–1.46 μg ml −1 ). Area under the curve (AUC) HPLC and AUC EMIT were normally distributed. Their mean was 52.42 ± 25.91 mg × h/l and their mean difference was 15.22 ± 8 mg × h/l (95%CI 11.99–18.45 mg × h/l), the Bland–Altman plot showing a bias proportional to the mean. Our data showed the absence of agreement between the HPLC and EMIT methods, with an average positive bias of 15% with the EMIT. Further studies are required to determine which method is best appropriate for TDM of MMF in children.