The C-3 epimer of 25-hydroxyvitamin D(3) is present in adult serum.

Context: Epimers have identical molecular structure but differ in stereochemical configuration. It is widely believed that the C-3 epimer of 25-hydroxyvitamin D(3) [3-epi-25(OH)D(3)] is found only in neonates. However, this epimer was recently detected in a limited number of adults.

NHANES monitoring of serum 25-hydroxyvitamin D: a roundtable summary.

A roundtable to discuss monitoring of serum 25-hydroxyvitamin D [25(OH)D] in the NHANES was held in late July 2009. Topics included the following: 1) options for dealing with assay fluctuations in serum 25(OH)D in the NHANES conducted between 1988 and 2006; 2) approaches for transitioning between the RIA used in the NHANES between 1988 and 2006 to the liquid chromatography tandem MS (LC-MS/MS) measurement procedure to be used in NHANES 2007 and later; 3) approaches for integrating the recently available standard reference material for vitamin D in human serum (SRM 972) from the National Institute of Standards and Technology (NIST) into the NHANES; 4) questions regarding whether the C-3 epimer of 25-hydroxyvitamin D3 [3-epi-25(OH)D3] should be measured in NHANES 2007 and later; and 5) identification of research and educational needs. The roundtable experts agreed that the NHANES data needed to be adjusted to control for assay fluctuations and offered several options for addressing this issue.

25-hydroxyvitamin D measurement, 2009: a review for clinicians.

As clinicians are more widely appreciating the endemic nature of low vitamin D status, measurement of serum 25-hydroxyvitamin D (25(OH)D), the accepted measure of vitamin D status, has increased. Challenges to 25(OH)D measurement include the presence of 2 forms of vitamin D-ergocalciferol and cholecalciferol (vitamin D(2) and vitamin D(3), respectively)- and the hydrophobic nature of vitamin D. The current state of 25(OH)D measurement is reviewed; modest differences between methodologies persist and confound the application of a single cut point (e.

Low vitamin D status despite abundant sun exposure.

Context: Lack of sun exposure is widely accepted as the primary cause of epidemic low vitamin D status worldwide. However, some individuals with seemingly adequate UV exposure have been reported to have low serum 25-hydroxyvitamin D [25(OH)D] concentration, results that might have been confounded by imprecision of the assays used.

Objective: The aim was to document the 25(OH)D status of healthy individuals with habitually high sun exposure.

HPLC method for 25-hydroxyvitamin D measurement: comparison with contemporary assays.

Background: The concentration of 25-hydroxyvitamin D [25(OH)D] in serum has been designated the functional indicator of vitamin D (VitD) nutritional status. Unfortunately, variability among 25(OH)D assays limits clinician ability to monitor VitD status, supplementation, and toxicity.

Methods: We developed an HPLC method that selectively measures 25-hydroxyvitamin D2 [25(OH)D2] and D3 [25(OH)D3] and compared this assay with a liquid chromatography-tandem mass spectrometry (LC-MS/MS) method, a competitive protein-binding assay (CPBA) on the Nichols Advantage platform, and an RIA from Diasorin.

Effective use of liquid chromatography-mass spectrometry (LC/MS) in the routine clinical laboratory for monitoring sirolimus, tacrolimus, and cyclosporine.

The authors describe an isocratic liquid chromatographic/electrospray single quadrupole mass spectrometric assay suitable for routine therapeutic monitoring of the antirejection drugs tacrolimus, sirolimus, and cyclosporine in blood. The drugs and added internal standards, ascomycin, desmethoxysirolimus, and cyclosporine G, are extracted from a protein-free supernatant of patient blood on a Strata SDB-L styrene-divinylbenzene polymeric extraction cartridge (Phenomenex, Torrance, CA). A Gilson Aspec XL-4 (Gilson Instruments, Middleton, WI) is programmed to perform the extraction and transfer the extract to autosampler vials.

Therapeutic monitoring of tacrolimus concentrations in blood: semi-automated extraction and liquid chromatography-electrospray ionization mass spectrometry.

The authors describe a highly selective liquid chromatographic/mass spectrometric (LC/MS) method for measurement of the immunosuppressive drug tacrolimus. A protein-free supernatant of a patient's whole-blood sample (500 microL) is applied to an Empore styrene-divinylbenzene (SDB-XC) disk cartridge (Varian Sample Preparation Products; Harbor City, CA) to isolate tacrolimus and the internal standard, ascomycin. The entire extraction is automated on the Gilson ASPEC XL4 (Gilson; Middleton, WI).

The effects of ketoconazole on the pharmacokinetics of cyclosporine A in cats.

Objective: To determine the effects of ketoconazole (KC) on the pharmacokinetics of cyclosporine A (CsA) elimination in cats.

Study Design: Research study and prospective clinical trial.

Animals: Five healthy adult cats (pharmacokinetic studies) and 6 client-owned cats with chronic renal failure.

Therapeutic monitoring of topiramate: evaluation of the saturable distribution between erythrocytes and plasma of whole blood using an optimized high-pressure liquid chromatography method.

Topiramate (TPM) reportedly binds in a saturable manner to erythrocytes but minimally to plasma proteins. Two studies were performed to evaluate this distribution phenomenon. In all studies, TPM was measured with a newly developed, optimized procedure that uses octyldecyl (C-18) solid phase sorbents disks/packed cartridges and a DB-1 methylsilicone capillary gas chromatography (GC) column.

Comparison of high performance liquid chromatography and immunoassay methods for measurement of cyclosporine A blood concentrations after feline kidney transplantation.

Objective: To compare two methods of whole blood cyclosporine A (CsA) measurement in cats.

Study Design: Whole blood samples were analyzed for CsA concentrations with use of high performance liquid chromatography (HPLC) and monoclonal immunoassay methods.

Animals: Blood (n = 36 samples) was obtained from six cats after renal transplantation.

Characterization of the peptide binding motif of a rhesus MHC class I molecule (Mamu-A*01) that binds an immunodominant CTL epitope from simian immunodeficiency virus.

The majority of immunogenic CTL epitopes bind to MHC class I molecules with high affinity. However, peptides longer or shorter than the optimal epitope rarely bind with high affinity. Therefore, identification of optimal CTL epitopes from pathogens may ultimately be critical for inducing strong CTL responses and developing epitope-based vaccines.

Optimized high-performance liquid chromatographic method for determination of lamotrigine in serum with concomitant determination of phenytoin, carbamazepine, and carbamazepine epoxide.

Lamotrigine (LG), phenytoin (PY), carbamazepine (CM), and carbamazepine epoxide (CE) are measured with an optimized procedure that uses thin sorbent extraction disks and a highly selective, sterically protected bonded silica high-performance liquid chromatography (HPLC) column. Routinely, serum (200 microliters at pH 6.8 with cyheptamide as internal standard) is applied to an Empore octyl (C8) solid-phase extraction disk to isolate the drugs.

Lamotrigine pharmacokinetics in patients receiving felbamate.

Drug interactions can significantly complicate the management of patients receiving multiple medications. It is essential therefore that potential pharmcokinetic interactions be evaluated as new antiepileptic medications are introduced. Lamotrigine (LTG) is a recently marketed medication whose pharmacokinetics are significantly influenced by concomitant drugs.

Effect of a high-protein meal on gabapentin pharmacokinetics.

The anticonvulsant gabapentin is transported across biological membranes via the L-amino acid transport system (System-L). Absorption of gabapentin is saturable, and in-vitro data have previously demonstrated that both L-leucine and L-phenylalanine may compete with the intestinal transport of gabapentin. The purpose of this study therefore was to determine whether a high-protein meal would interfere with gabapentin absorption.

Optimized method for determination of gabapentin in serum by high-performance liquid chromatography.

The anticonvulsant drug gabapentin and its heptaneacetic acid analog-used here as an internal standard--are isolated from serum (pH 9) with an octyldecyl (C-18) solid-phase sorbent column. To enhance analytical detection, trinitrobenzene derivatives of these extracted compounds are prepared quickly within 10 min. To further improve chromatographic selectivity, the derivatives are concentrated on a thin C-18 solid-phase membrane and interferences are washed away.

Use of particle-loaded membranes to extract steroids for high-performance liquid chromatographic analyses improved analyte stability and detection.

Cortisol, cortisone, corticosterone, prednisone and prednisolone are extracted from serum using the novel particle-loaded octyl (C8)-bonded silica in PTFE membrane. Extracts are directly injected, without further concentration, onto a narrow (2.0 mm) or conventional (4.

Application of the Empore solid-phase extraction membrane to the isolation of drugs from blood: II. Mexiletine and flecainide.

A stabilized therapeutic drug monitoring procedure incorporating the novel Empore solid-phase extraction membrane (SPEM) for isolation of the antiarrhythmic drugs mexiletine (MEX) and flecainide (FLEC) from serum is described. Routinely, serum (0.5 ml), adjusted to pH 4.

Application of a novel form of solid-phase sorbent (Empore membrane) to the isolation of tricyclic antidepressant drugs from blood.

We employed a new form of solid-phase material, the Empore octyl (C8) extraction membrane (SPEM), for the efficient extraction of tricyclic drugs from patients' serum specimens. Both extraction and companion high-performance liquid chromatographic (HPLC) assay of doxepin (DOX), desmethyldoxepin (DDOX), imipramine (IMI), desmethylimipramine (DESI), amitriptyline (AMI), nortriptyline (NOR), clomipramine (CLO), and desmethylchlomipramine (DCLO) are presented here. Routinely, serum (1.

Synergistic and antagonistic effects of combinations of cyclosporine A and its metabolites on inhibition of phytohemagglutinin-induced lymphocyte transformation in vitro.

Cyclosporine A (CsA) and purified CsA metabolites were tested alone and in combination in cell culture to determine their effects on phytohemagglutinin (PHA)-induced lymphocyte proliferation. CsA was significantly more inhibitory than its metabolites at all concentrations tested (0-1000 ng/mL). CsA exerted maximum inhibition (70% decrease in [methyl-3H]thymidine incorporation) at concentrations of 300 ng/mL or greater; metabolites M1, M17, and M21 depressed the response 46, 39, and 23%, respectively, at 300 ng/mL.

Concentrations of cyclosporin A and its metabolites in human tissues postmortem.

We report concentrations and distribution of cyclosporine A (CsA) and individual metabolites associated with various organ tissues and whole-blood specimens collected at autopsy from seven transplant patients who received CsA therapy. Solid-phase extraction (SPE) and specific high-performance liquid chromatographic (HPLC) procedures were used to separate and quantitate the cyclosporines. Patterns of deposition were unique for the various tissue types.

Application of the Empore solid-phase extraction membrane to the isolation of drugs from blood. I. Amiodarone and desethylamiodarone.

We describe the use of a new form of solid-phase material, the Empore solid-phase extraction membrane (SPEM), for therapeutic drug monitoring. We evaluated the new extraction procedure with the companion high-performance liquid chromatographic (HPLC) method for the antiarrhythmic drug amiodarone and its metabolite, desethylamiodarone, in patients' serum. Acidified serum (250 microliters) was passed through an octyl (C8) SPEM secured in an MF-1 microfilter unit.

Three commercial polyclonal immunoassays for cyclosporine in whole blood compared: 2. Cross-reactivity of the antisera with cyclosporine metabolites.

We demonstrate the diverse selectivity of three commercial polyclonal "cyclosporine" immunoassays for cyclosporin (CsA) metabolites by comparing analytical responses of nine metabolites added to drug-free whole-blood specimens (range 0 to 2000 micrograms/L) and assayed by the Abbott TDx fluorescence polarization immunoassay (FPIA), the Incstar Cyclo-Trac radioimmunoassay (RIA), and the Sandoz RIA. Cross-reactivity--defined as the relative response (slope of regression line) of metabolite/parent CsA over the assay's linear range of concentrations--differed for each metabolite among the three assays. Overall, Abbott's antiserum exhibited the greatest affinity for the metabolites, the Sandoz antiserum the least.

Three commercial polyclonal immunoassays for cyclosporine in whole blood compared: 1. Results with patients' specimens.

We assessed the performance of three commercially available polyclonal immunoassays for apparent cyclosporine in 120 whole-blood specimens collected from transplant recipients just before their next dose of cyclosporine (CsA). The assays were (a) Abbott's TDx fluorescent polarization immunoassay for CsA and its metabolites in whole blood; (b) the Sandoz radioimmunoassay (RIA); and (c) Incstar's Cyclo-Trac RIA. Mean respective CVs were 3.