Adsorption of Mycophenolic Acid and Its Phenolic Glucuronide to Glass, Polystyrene, and Polypropylene Containers

Abstract

a second-generation electrochemiluminescence PTH assay on the Elecsys 2010 platform (Roche Diagnostics). Ionized calcium and 25-hydroxyvitamin D (Nichols Advantage) were also measured in all samples.Results for the healthy individuals are presented in Fig. 1. The bio-intact PTH values measured by the IRMA and chemiluminescence immunoassay were, on average, 50% and 30% lower, respectively, than the PTH measured by the Elecsys. Regression analysis demonstrated significantly different slopes (P Ͻ0.001), but not intercepts, for both the IRMA and chemiluminescence immunoassay compared with the Elecsys assay. Most striking was the discordance between the ELISA and the IRMA, the chemiluminescence immunoassay, and the Elecsys assay. Comparison between the ELISA and Elecsys revealed a significantly different intercept (P Ͻ0.001). The results obtained with the third-generation IRMA and the chemiluminescence immunoassay also differed, despite the good correlation, and regression analysis demonstrated a significant difference for the slope (P Ͻ0.001) but not for the intercept. The finding of higher results with the chemiluminescence immunoassay concurs with the results reported by Boudou et al. (3 ), but immunoreactivity does not seem to be implicated in these differences (1-3 ). In addition to the apparent differences in assay design, other possible reasons for the lack of agreement between the assays investigated could be matrix effects and/or differences in standardization. The problems hampering immunoassay standardization are many and vary for different analytes, as has been reviewed by Stenman (4 ). Thus, the use of independent reference intervals for each of the bio-intact PTH assays is clinically important.We observed no significant differences between healthy individuals and patients with predialysis chronic kidney disease for 25-hydroxyvitamin D, but mean concentrations of bio-intact PTH (by chemiluminescence immunoassay; P Ͻ0.001) and ionized calcium (P Ͻ0.05) were higher in the patients. PTH measured by Elecsys was, on average, 75% higher than the measured biointact PTH in patients, consistent with the expected presence of high concentrations of circulating PTH fragments in patients with impaired renal function. In addition, the distribution of bio-intact PTH analyzed by the chemiluminescence immunoassay (mean, 71 ng/L; range, 5-227 ng/L) was wider in the patient group than in the healthy individuals [23 (11-50) Despite our strict adherence to the ELISA protocol and 3 independent runs with the same set of samples, this assay generated inconsistent results, which require additional methodologic studies to fully explain. We conclude that although the thirdgeneration bio-intact PTH ELISA requires further evaluation, the chemiluminescence immunoassay and IRMA are comparable.

Optimal Storage Temperature and Matrix Before Analyzing Mycophenolic Acid

“…Analogous degradative processes might also explain the falls in MPA concentrations observed during longer-term storage. An alternative possibility, that MPA is lost after adsorption to the surface of the polypropylene tubes we used, 19 seems less likely because losses were reported to occur only at the first contact, not increasingly with time as observed here.…”

Evaluation of MPA and MPAG Removal by Continuous Venovenous Hemodiafiltration and Continuous Venovenous Hemofiltration

“…Total MPA and total MPAG concentrations were determined by HPLC with a previously described method, 13 for which the limits of quantification (0.1 mg/L for MPA and 0.8 mg/L for MPAG) were improved by the use of polystyrene tubes to avoid drug adsorption, as previously reported, 14 and to lower dilution of the sample prior to injection. Plasma and ultrafiltrate levels of free MPA and free MPAG were assessed by the method previously described, which is linear over the range of 0.005 to 5 mg/L for MPA and 0.05 to 200 mg/L for MPAG.…”