Population pharmacokinetics of mycophenolic acid in lung transplant recipients with and without cystic fibrosis.

PURPOSE: The objective of this work was to characterize and compare the population pharmacokinetics (PK) mycophenolic acid (MPA) in adult lung transplant recipients with cystic fibrosis (CF) and without the disease (NCF) following repeated oral administration of the prodrug mycophenolate mofetil (MMF) as an immunosuppressant. METHODS: Three separate 12-h PK visits were conducted for lung transplant patients with or without CF following repeated MPA treatment with at least a 2-week break between the visits. A population PK model was developed using nonlinear mixed effects modeling (NONMEM), and the contribution of physiological and pathological factors and time dependence of apparent oral clearance (CL/F) were assessed. RESULTS: For both CF and NCF patients, MPA serum concentration-time profiles were best described by a two-compartment PK model with first-order absorption. CF patients had a slower absorption rate (Ka), and elevated CL/F and volume of distribution (Vd/F) compared with NCF patients. There is a significant contribution of body weight and CF disease to MPA CL/F, and both were included in the final model as covariates. CONCLUSIONS: The population PK model developed from our study successfully characterizes the absorption, distribution, and elimination of MPA in lung transplant recipients with or without CF disease. The decrease of MPA absorption and increase of both oral clearance (CL/F) and volume of distribution (V2/F and V3/F) in the CF patients would suggest the importance of MPA therapeutic monitoring for this group.

Evaluation of high-resolution mass spectrometry for urine toxicology screening in a pain management setting.

To evaluate liquid chromatography-high-resolution mass spectrometry (LC-HR-MS) for urine toxicology screening, 29 analytes were quantitated in 152 urine specimens from patients with chronic pain using two unique mass spectrometry platforms. De-identified specimens were quantitated in April of 2011 by liquid chromatography-triple quadrupole mass spectrometry (LC-MS-MS) and by full-scan LC-HR-MS at Millennium Laboratories. Considering LC-MS-MS as the reference method, false positive results were identified in 19 specimens measured by LC-HR-MS. Application of relative retention times using deuterium labeled internal standards improved the rate of false positive detection to only five specimens, with four occurring for the same analyte. Ultra-high-resolution mass spectrometry (R = 100,000 at m/z 200) showed no improvement over high-resolution mass spectrometry (R = 10,000 at m/z 200) in the number of false positives detected. Quantitative results measured by LC-MS-MS and LC-HR-MS showed good agreement over four orders of dynamic range. This study demonstrates that LC-HR-MS is a suitable platform for toxicology screening for a pain management population and that quantitative accuracy and sensitivity are comparable to that achieved with LC-MS-MS. The specificity of LC-HR-MS is improved by the addition of deuterium labeled internal standards and the implementation of relative retention time matching.