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S J Soldin

Publications and source records attributed to S J Soldin.

At least 37 records · Page 2Linked to original sources
PubMed1998

Tacrolimus metabolite cross-reactivity in different tacrolimus assays.

OBJECTIVES: Tacrolimus (FK506) is an immunosuppressive drug with great clinical promise. There is a controversy regarding the role of tacrolimus metabolites in immunosuppression and toxicity, and immunoassays and immunophilin binding assays have not been adequately tested for metabolite cross-reactivity. Methods are limited to HPLC and HPLC-MS for quantifying the parent drug. Mixed lymphocyte culture assay (MLC) is the preferred functional bioassay for the measurement of parent drug and active metabolites but it is not practical for routine laboratory use. Due to differences in assay methods and reagent specificity, the concentration of tacrolimus in a given specimen may vary among different assay kit manufacturers. The objective of this study was to evaluate the degree of cross-reactivity or interference of the three first-generation tacrolimus metabolites [13-O-demethyl (M-I), 31-O-demethyl (M-II) and 15-O-demethyl (M-III)] among two different tacrolimus immunoassays (Immunoassay: PRO-Trac II FK506, Abbott IMx tacrolimus-II); and the radioreceptor assays (RRA) using minor immunophilins (14, 37, and 52 kDa immunophilins) and tacrolimus binding protein (FKBP12). METHODS: First-generation tacrolimus metabolites (M-I, M-II, and M-III) spiked in drug-free whole blood were assayed with RRA using three minor immunophilins (14, 37, and 52 kDa) and two commercial immunoassay procedures (Incstar PRO-Trac II tacrolimus, Abbott IMx tacrolimus II). The results were compared to previously published FKBP-12 RRA data and their immunosuppressive potency. RESULTS AND CONCLUSION: The first generation tacrolimus metabolites (M-I, M-II, and M-III) were tested using concentrations of 10 and 20 ng/mL. The significance of the metabolite interference (% of the total interference) was calculated based on the relative concentration of each metabolite present at steady-state trough concentrations in renal transplant recipients (22). Metabolite I, which has no functional immunosuppressive activity showed minimal interference compared to M-II and M-III in all assays except the 14 kDa RRA. The Incstar PRO-Trac II tacrolimus assay showed the least M-I interference. Metabolite-II, which has a pharmacologic potency similar to the parent drug, showed a significant interference in the immunoassays and significant interference in radioreceptor assays. Metabolite III, which is pharmacologically inactive, produces 3-10% interference in the different assays if its presence in the blood is 6% of the parent drug. The total interference from these three metabolites was greater in the immunoassays than in the receptor assays. Receptor assays for tacrolimus provide results closer to the target value than do immunoassays.

Cross Reactions↗
PubMed1998

Strategies for physician education in therapeutic drug monitoring.

Although therapeutic drug monitoring (TDM) is probably very useful overall, studies suggest that it could be used better. Many drug concentrations appear to have inappropriate indications or suboptimal timing, particularly in the inpatient setting. Undermonitoring is also a concern. Thus, it may be possible to both improve the quality of TDM and reduce the overall costs of care. Here we review approaches for improving the use of TDM and present some illustrative experiences. Specific approaches discussed include use of traditional approaches such as lectures and newsletters, multidisciplinary quality improvement efforts, formal TDM services, and use of the computer as a tool for education and behavior change. Computerized methods appear to hold substantial potential, particularly as more organizations develop better information systems, but other approaches are also effective and are complementary. To be most successful, interventions should consider all stages of the process.

Canada↗
PubMed1997

Identification of a 37 kDa tacrolimus, sirolimus and cyclosporine binding immunophilin possessing glyceraldehyde 3-phosphate dehydrogenase activity isolated from the Jurkat T cell line.

OBJECTIVE: The isolation and partial characterization of a 37 kDa minor immunophilin from the Jurkat cell line which binds to cyclosporine (CsA), Tacrolimus (FK506) and Sirolimus (RAPA). DESIGN AND METHODS: Using standard protein purification steps including isoelectric focusing and cation exchange chromatography, we have isolated and purified to homogeneity a minor immunophilin from the Jurkat cell line which has a molecular weight of 37 kDa. Binding properties for immunosuppressive drugs CsA, FK506 and RAPA were assessed by Scatchard and displacement analysis. The amino acid analysis and the protein sequences were also studied. RESULTS: The immunophilin was purified to homogeneity and the molecular weight corresponds to 37 kDa. Saturation experiments using 3Hdihydro FK506 gave a Kd of 4.5 nM and the Bmax of 117 nmol/mg protein. Displacement studies using 3Hdihydro FK506 and RAPA gave a Kd of 0.8 nM. For CsA binding, the protein showed somewhat less avid binding. The amino acid composition was in close agreement with the amino acid composition of uracil DNA glycosylase which corresponds to part of the monomer of glyceraldehyde 3 phosphate dehydrogenase (G3PD). Protein digestion gave at least 3 peptides. The primary sequence of the first of these matched 7 of 8 residues of human liver nuclear uracil DNA glycosylase. The 37 kDa immunophilin was found to have G3PD activity not inhibited by FK506. CONCLUSIONS: The amino acid analysis, protein sequences, binding properties and G3PD activity indicate that this 37 kDa immunophilin is different from any other known immunophilins.

Adjuvants, Immunologic↗
PubMed1997

Evaluation of i-STAT portable clinical analyzer in a neonatal and pediatric intensive care unit.

OBJECTIVE: To evaluate the Point-of-Care (POC) i-STAT system for measuring blood gases (pH, pCO2, pO2) and whole blood electrolytes (sodium, Na+, potassium, K+ and ionized calcium, iCa2+) in the neonatal and pediatric intensive care units. DESIGN AND METHODS: The i-STAT system was evaluated for imprecision, necessity of running quality control and accuracy. Comparison of patients' samples analyzed by the i-STAT system and the Ciba Coming 288 blood gas analyzer were performed. The reliability of the i-STAT system when performed by non-laboratory personnel was assessed. RESULTS: The system was evaluated for imprecision and linearity using three concentrations of aqueous standards. Except for pO2, the %CVs were < 3.0 for all the analytes (pH, pCO2, Na+, K+ and iCa2+) at all the three concentrations. Using whole blood studies the precision data gave %CVs that were < 3.5 for all the analytes. Linearity studies showed good linearity over the five different concentrations tested. Comparison of the i-STAT and the Ciba Coming 288 blood gas analyzer was assessed by split sample measurement. Patients' results from the i-STAT correlated well with the Ciba Coming 288 blood gas analyzer (r = 0.99 for pH, pCO2 and pO2 and 0.95 to 0.99 for Na+ and K+) with the exception of iCa2+ (r = 0.73). There was no significant difference in the results when operated by PICU/NICU nurses or laboratory personnel. A further study was made to assess whether routine quality control (QC) samples are necessary when using the i-STAT system. The regression analysis (slope and correlation coefficient) of the results from instruments run with and without QC samples gave results close to 1, indicating that there is no need to run additional quality control (QC). CONCLUSION: The POC testing analyzer i-STAT is a reliable alternative to the traditional blood gas analyzers and provides marginal improvement in turnaround time when compared with the service received from the PICU/NICU laboratory. Costs need to be carefully controlled.

Blood Gas Analysis↗
PubMed1997

Radioreceptor assay for sirolimus in patients with decreased platelet counts.

OBJECTIVE: Sirolimus (RAPA) is a new immunosuppressive drug currently in Phase III clinical trials in combination with cyclosporine A (CsA). The toxicity profiles for CsA and RAPA are only partially overlapping, with RAPA toxicity consisting primarily of hyperlipidemia and myelodepression but without the nephrotoxicity, neurotoxicity, and hepatotoxicity, which are seen with CsA. Patients in the clinical trial are being monitored using HPLC or LC/MS/MS assays; there is no immunoassay for RAPA reported to date. We have previously reported a radioreceptor assay (RRA) for RAPA, which has an excellent correlation with the HPLC assay (r = 0.997). The RRA has several advantages including excellent precision, sensitivity, rapid turnaround time, and a one-step extraction procedure. We report the evaluation of blood samples from patients who were exhibiting RAPA toxicity and comparison of the RRA results with the HPLC results. METHODS: EDTA whole blood specimens (n = 42) were obtained from six renal transplant recipients taking RAPA and CsA and exhibiting decreased platelet counts. Thirty-two samples from patients without decreased platelet counts were also received. The samples were analyzed with the RRA and the results were compared to those obtained with the HPLC assay. RESULTS: By HPLC, the results ranged from 3.2-72.6 micrograms/L RAPA with 43% of the results > or = 30 micrograms/L. With the RRA, the range was 7.7-83.0 micrograms/L RAPA equivalents, with 60% of the results > or = 30 micrograms/L. The RRA results are distinctly higher than the HPLC results all along the range. The correlation between the two assays was 0.861, with a slope of 0.966 and a Y-intercept of 11.1. CONCLUSION: Since the RRA is consistently higher than HPLC concentration in patients with decreased platelet counts, but correlates well in patients with no signs of toxicity, the RRA may be useful for monitoring patients for toxicity, by giving a better indication of increasing degree of immunosuppression than the HPLC assay.

Chromatography, High Pressure Liquid↗
PubMed1996

The role of lipoproteins in the transport and uptake of cyclosporine and dihydro-tacrolimus into HepG2 and JURKAT cell lines.

OBJECTIVES: We wish to examine the role of lipoproteins in the transport and cellular uptake of cyclosporine (CsA) and tacrolimus. DESIGN AND METHODS: The distribution of tritiated CsA and tacrolimus among lipoproteins was determined in normo- and hypertriglyceridemic sera. The uptake of these two drugs into HepG2 and JURKAT cell lines was assessed in the presence of various concentrations of low density lipoproteins. (LDL). RESULTS: Our data showed that about 60% of these drugs were transported by high density lipoprotein in normolipidemic sera, while about 50-60% were carried by very low density lipoprotein in hypertriglyceridemic sera. Almost 80% of CsA and 70% of tacrolimus entered HepG2 and JURKAT cells within the first hour of incubation in lipoprotein free media. However, the uptake was decreased (CsA by 60% and tacrolimus by 40%) in the presence of LDL. CONCLUSIONS: Lipoproteins play a major role in the transport of CsA and tacrolimus, but not in their cellular uptake.

Biological Transport, Active↗
PubMed1996

Comparison of binding characteristics of four rapamycin metabolites to the 14 and 52 kDa immunophilins with their pharmacologic activity measured by the mixed-lymphocyte culture assay.

OBJECTIVES: To compare the binding characteristics of four rapamycin (RAPA) metabolites to the 14 and 52 kDa minor immunophilins with their pharmacologic activity, as measured by the mixed-lymphocyte culture (MLC) assay. METHODS: Four RAPA metabolites were isolated by HPLC from the urine of renal transplant patients. Each metabolite was evaluated at 40 micrograms/L for its pharmacologic activity using the MLC assay. The results of the MLC assay were compared to those obtained using the radioreceptor assay (RRA), which measured the binding characteristics of equal concentrations of the metabolites to the 14 and 52 kDa minor immunophilins. RESULTS: Each of the four RAPA metabolites showed low immunosuppressive activity by MLC. RM2 showed the highest activity, with 9% of parent RAPA activity. RM1, 3, and 4 showed 2%, 8%, and 4% activity, respectively. Only RM1 was found to bind significantly to either minor immunophilin, with 21% of parent binding to the 14 kDa protein and 25% of parent binding to the 52 kDa protein. RM2, 3, and 4 bound to both proteins with < or = 2% of parent binding. CONCLUSION: We have demonstrated that the RRA for these four RAPA metabolites shows little cross-reactivity. There is no commercially available immunoassay for RAPA at present. The RRA, therefore, provides an excellent way to rapidly assess efficacy/toxicity of RAPA in patients receiving the drug.

Binding, Competitive↗
PubMed1996

Receptor assays in the clinical laboratory.

OBJECTIVE: To review the relative advantages/disadvantages of receptor assays versus immunoassays. REVIEW OF CURRENT LITERATURE RESULTS: The history of immunoassays is evaluated. Current shortcomings are emphasized. The present and future role of receptor assays is assessed. CONCLUSION: The author predicts a shift away from immunoassays to receptor assays for certain analytes such as Vitamin B12, folic acid and drugs that undergo extensive metabolism.

Anti-Arrhythmia Agents↗
PubMed1996

Radioreceptor assay for sirolimus.

OBJECTIVES: To develop a radioreceptor assay (RRA) for sirolimus (rapamycin, RAPA). METHODS: A direct methanol extraction was used to prepare 45 patient samples for the RRA. Results were compared to the results obtained previously using high-performance liquid chromatography (HPLC). Between-run precision, recovery, and drug interference studies were also performed. RESULTS: The RRA is sensitive to 1.0 microgram/L RAPA equivalents in whole blood. Comparison with HPLC yielded a correlation coefficient for 45 patient samples of 0.977. Between-run precision at 2.5, 7.5, 12.5, and 20 micrograms/L showed coefficients of variation (CVs) of 12.9, 9.2, 8.5, and 5.9%, respectively. Recoveries from the extraction procedure were 93% at 7.5 micrograms/L and 103% at 12.5 micrograms/L. Drug interference studies showed no interference in the RRA by cyclosporine (CsA), dexamethasone, prednisone, or methotrexate. CONCLUSION: We have demonstrated that the RRA for RAPA correlates well with HPLC, and has excellent precision and recovery. The procedure is far less time-consuming and complex than HPLC and has potential for automation.

Carrier Proteins↗
PubMed1996

Emergency department evaluation of a rapid assay for detection of cocaine metabolites in urine specimens.

We evaluated the Abuscreen ONTRAK assay for cocaine metabolites, a rapid immunoassay for the detection of cocaine metabolites in a pediatric emergency department (ED) setting. The ONTRAK uses a cutoff point of 300 micrograms/L for benzoylecgonine (BEC), cocaine's major urinary metabolite. One hundred and thirty-two urine specimens obtained from infants, children, and adolescents whose clinical findings warranted toxicology screening were evaluated. The ONTRAK identified all 15 specimens with BEC values of 300 micrograms/L, but did not detect seven additional specimens positive for cocaine metabolites at concentrations less than 300 micrograms/L. One third of the positive specimens for cocaine metabolite identified by fluorescent polarization immunoassay (FPIA), cutoff point set at 80 micrograms/L, and confirmed by gas chromatography/mass spectrometry (GUMS), cutoff point 50 micrograms/L, were not detected by the ONTRAK. These false negative specimens were seen exclusively in young children, whose concentration of cocaine metabolite was less than the ONTRAK's cutoff value. The test was sensitive to drug concentration at or around the stated cutoff values. The ONTRAK test for cocaine metabolites, although both a sensitive and specific screening test for adolescents who smoke or snort cocaine, lacks the sensitivity to be a useful screening too[ for detecting cocaine metabolites in young children. Limitations of currently performed toxicology screening tests (ie, stated cutoff levels) may cause emergency physicians to miss most young children whose symptoms may he related to cocaine exposure.

Adolescent↗
PubMed1995

Evaluation of the Technicon Immuno I random access immunoassay analyzer and calculation of pediatric reference ranges for endocrine tests, T-uptake, and ferritin.

OBJECTIVES: Evaluation of the precision, accuracy, and user-friendliness of the Technician Immuno I. Calculation of pediatric reference ranges for ferritin and endocrine tests run on Immuno I. METHODS: Precision and accuracy were measured using controls and method comparison studies. Pediatric reference ranges were calculated by comparing the Immuno I results for 100 patients with those of the Abbott IMx and TDx. The regression equation obtained was then used to convert the IMx and TDx reference ranges to reference ranges for the Immuno I. RESULTS: The Immuno I provided both accurate and precise measurement of drugs and endocrine hormones. Pediatric reference ranges were obtained for ferritin and all endocrine tests. CONCLUSION: The Immuno I is user-friendly and provides reliable measurement of both the drugs tested and endocrine tests on a micro-sample. Reagent and curve stability are excellent.

Adolescent↗
PubMed1995

Preliminary assessment of glycine conjugation of para-aminobenzoic acid as a quantitative test of liver function.

OBJECTIVES: Our hypothesis is that because of its hepatic metabolism paraaminobenzoic acid (PABA) could be a test of liver function. DESIGN AND METHODS: PABA is well absorbed by the gastrointestinal tract and acetylated and conjugated in the liver to glycine before being excreted. Its three major metabolites include para-acetoamidobenzoic acid (PAABA), paraaminohippuric acid (PAHA), and paraacetamidohippuric acid (PAAHA). In this study, we measured the metabolism of lidocaine to monoethylglycinexylidide (MEGX) and PABA to PAHA+PAAHA/PABA+PAABA+PAHA+PAAHA (hippurate ratio) in 14 patients with liver disease and 12 control subjects. RESULTS: Comparison of the total bilirubin with the hippurate ratio (at 30 min) and the conventional MEGX test (at 15 min) was assessed. The 30 min hippurate ratio correlated well with the 15 min MEGX results (r = 0.69). CONCLUSIONS: While these results are preliminary the PABA test appears to be equally sensitive to MEGX and has the distinct advantage over the MEGX test of being administered orally versus the intravenous administration of lidocaine which is often associated with unwanted side-effects such as hypotension, drowsiness and paresthesias.

4-Aminobenzoic Acid↗
PubMed1995

Glycine conjugation of para-aminobenzoic acid (PABA): a quantitative test of liver function.

OBJECTIVE: To evaluate glycine conjugation of para-aminobenzoic acid (PABA) to the hippurated metabolites, para-aminohippuric acid (PAHA), and para-acetamidohippuric acid (PAAHA) as a quantitative liver function test in patients with liver disease. DESIGN AND METHODS: Serum concentrations of PABA and metabolites were measured by high pressure liquid chromatography in 24 controls and 50 patients with hepatobiliary disease. RESULTS: Hippurate formation was significantly decreased in all patient groups with chronic liver disease versus controls. The hippurate ratio (% hippurated metabolites formed) correlated with severity of disease, serum albumin, and factor VII concentrations. PAHA concentration was a better prognostic indicator than factor VII concentrations in patients with acute liver disease; concentrations of zero correctly predicted a poor outcome in patients with fulminant liver failure. CONCLUSIONS: Glycine conjugation of PABA may be useful as a quantitative liver function test in patients with hepatobiliary disease and as a prognostic index in patients with fulminant liver failure.

4-Aminobenzoic Acid↗
PubMed1995

Plasma erythropoietin reference ranges in children.

Plasma erythropoietin values were determined in 1122 hospitalized and outpatient children aged 1 to 18 years with a commercially available enzyme-linked immunosorbent assay. A computerized approach based on the Hoffman technique was used to establish erythropoietin reference ranges. Plasma erythropoietin values ranged from 1.0 to 21.9 mIU/ml in male subjects, and from 1.1 to 20.5 mIU/ml in female subjects (2.5th to 97.5th percentiles).

Adolescent↗
PubMed1995

Receptor (immunophilin-binding) assay for immunosuppressive drugs.

The major immunophilins that bind cyclosporine (cyclophilin) and FK-506/rapamycin (FK-BP12) have been well characterized. They possess rotamase activity, which is inhibited by the immunosuppressant that binds to them. The immunosuppressive action does not appear to be coupled to rotamase activity. The literature on some possible mechanisms of immunosuppression is reviewed. Minor immunophilins of 14, 37, and 52 kDa have also been isolated and partially characterized. The 14-kDa immunophilin binds FK-506 and rapamycin whereas the 52-kDa immunophilin binds all three drugs. Neither of these proteins have rotamase activity. Receptor assays employing immunophilins have been developed. Preliminary results are encouraging indicating that they may possess some advantages over current immunoassay procedures.

Amino Acid Isomerases↗