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P Salm

Publications and source records attributed to P Salm.

15 recordsLinked to original sources
PubMed2001

A retrospective analysis of mycophenolic acid and cyclosporin concentrations with acute rejection in renal transplant recipients.

OBJECTIVES: Although monitoring of cyclosporin (CsA) is standard clinical practice postrenal transplantation, mycophenolic acid (MPA) concentrations are not routinely measured. There is evidence that a relationship exists between MPA area under the concentration-time curve (AUC) and rejection. In this study, a retrospective analysis was undertaken of 27 adult renal transplant recipients. METHODS: Patients received CsA and MPA therapy and had a four-point MPA AUC investigation. The relationship between MPA AUC performed in the first week after transplantation, as well as median trough cyclosporin concentrations, and clinical outcomes in the first month posttransplant were evaluated. RESULTS: A total of 12 patients experienced biopsy proven rejection (44.4%) and 4 patients had gastrointestinal adverse events (14.8%). A statistically significant relationship was observed between the incidence of biopsy proven rejection and both MPA AUC (p = 0.02) and median trough CsA concentration (p = 0.008). No relationship between trough MPA concentration and rejection was observed (p = 0.21). Only 3 of 11 (27%) patients with an MPA AUC > 30 mg x h/L and a median trough CsA > 175 microg/L experienced acute rejection, compared with a 56% incidence of rejection for the remaining 16 patients. Patients who experienced adverse gastrointestinal events had significantly lower MPA AUC (p = 0.04), but median trough CsA concentrations were not significantly different (p = 0.24). Further, 3 of these 4 patients had rejection episodes. CONCLUSIONS: In addition to standard CsA monitoring, we propose further investigation of the use of a 4-point sampling strategy to predict MPA AUC in the first week posttransplant, which may facilitate optimization of mycophenolate mofetil dose at a time when patients are most vulnerable to acute rejection.

Adult↗
PubMed2001

A detection scheme for paraquat poisoning: validation and a five-year experience in Australia.

We report the validation of a quantitative method for paraquat in plasma and urine using high-performance liquid chromatography (HPLC) with ultraviolet detection (260 nm). Furthermore, we illustrate the use of this method in the clinic (over five years), in conjunction with a qualitative urine paraquat screen. Urine or plasma sample (1 mL) preparation was performed in duplicate using C18 solid-phase extraction. Chromatographic separation was achieved on a Zorbax RX-Silica column (250 x 4.6-mm i.d.). The mobile phase consisted of 96% sodium chloride (5 g/L) and 4% acetonitrile (pH 2.2) pumped at 1.0 mL/min. Using a single-point calibration (1.0 mg/L), the method was found to be linear from 0.1 to 5.0 mg/L. The accuracy and imprecision of the method, over the linear range and for plasma and urine, were 94.7-104.9% and < 12.2%, respectively. The limit of quantitation for both matrices was 0.1 mg/L. The absolute recovery of paraquat from plasma and urine was 79.9 +/- 5.3% and 88.2 +/- 5.3%, respectively. From January 1995 to February 2000, 47 qualitative urine paraquat screens were requested throughout Australia. Nine screens were positive, and eight were confirmed to have paraquat present by our HPLC method. One sample was not analyzed by HPLC because the patient died prior to analysis. Thus, no false-positive results were reported for the qualitative urine screen. An additional 11 samples were referred for patients with positive screens from other sites for HPLC confirmation. The presence of paraquat was confirmed in nine of these samples. In conclusion, a qualitative urine screen combined with our validated HPLC confirmation is an effective protocol for assessing suspected cases of paraquat poisoning.

Calibration↗
PubMed2000

Quantification of free mycophenolic acid by high-performance liquid chromatography-atmospheric pressure chemical ionisation tandem mass spectrometry.

To facilitate the investigation of free mycophenolic acid concentrations we developed a high-performance liquid chromatography tandem mass spectrometry method using indomethacin as an internal standard. Free drug was isolated from plasma samples (500 microl) using ultrafiltration. The analytes were extracted from the ultrafiltrate (200 microl) using C18 solid-phase extraction. Detection was by selected reactant monitoring of mycophenolic acid (m/z 318.9-->190.9) and the internal standard (m/z 356.0-->297.1) with an atmospheric pressure chemical ionisation interface. The total chromatographic analysis time was 12 min. The method was found to be linear over the range investigated, 2.5-200 microg/l (r>0.990, n=6). The relative recovery of the method for the control samples studied (7.5, 40.0 and 150 microg/l) ranged from 95 to 104%. The imprecision of the method, expressed in terms of intra- and inter-day coefficients of variation, was <8 and <9%, respectively. Further, analysis of pooled patient plasma produced an intra-day imprecision of 6.6%. The signal-to-noise ratio at the limit of quantification (2.5 microg/l) was approximately 5:1. The mean absolute recovery (n=6) of mycophenolic acid and the internal standard were 76.0+/-13.5% and 86.0+/-9.1%, respectively. The method reported provides an accurate and precise quantification of free mycophenolic acid over a wide analytical range and thus can be used for routine monitoring and pharmacokinetic studies.

Atmospheric Pressure↗
PubMed2000

Evaluation of microparticle enzyme immunoassay against HPLC-mass spectrometry for the determination of whole-blood tacrolimus in heart- and lung-transplant recipients.

OBJECTIVES: Tacrolimus is an immunosuppressant drug with a narrow therapeutic window and thus requires therapeutic drug monitoring. This study evaluates the suitability of the second-generation microparticle enzyme immunoassay (MEIA II) against a specific method, high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS), for the measurement of tacrolimus in both heart- and lung-transplant groups. A secondary objective was to investigate the effect of tacrolimus concentration on MEIA II measurement. METHODS: The HPLC-MS assay was conducted as per our reported method and MEIA II performed according to manufacturer's instructions. Quality-control samples at 5, 11, and 22 microg/L were run in each batch to ensure assay integrity in both methods. Multiple trough samples from 18 heart patients (n = 126) and 17 lung patients (n = 203) were analyzed. RESULTS: The inter-batch imprecision and analytical recovery over the quality-control range by HPLC-MS (n = 12) was <6% and 98.2% to 104%, respectively, and by MEIA II (n = 16) <15% and 92.0% to 99.1%, respectively. The mean overestimation by MEIA II between the two methods for heart- and lung-transplant patient samples was found to be 9.9% (range: -37.4-45.4%) and 13.2% (range: -29.2-64.3%), respectively. Stratification of these data based on the tacrolimus concentration determined by MEIA II, yielded no statistically significant differences in bias between concentration subgroups within the clinically relevant range (p > 0.4). However, a statistically significant difference was detected between the highest concentration subgroup (>20.0 microg/L) and lower concentration subgroups in both transplant populations (p < 0.05). CONCLUSIONS: This study suggests that where HPLC-MS is not available, MEIA II may be suitable for the therapeutic drug monitoring of tacrolimus in heart- and lung-transplant recipients. However, the clinical importance of the observed mean bias, considering the wide range in overestimation in heart- and lung-transplant patient samples, is yet to be determined.

Adolescent↗
PubMed2000

The quantification of sirolimus by high-performance liquid chromatography-tandem mass spectrometry and microparticle enzyme immunoassay in renal transplant recipients.

BACKGROUND: Sirolimus, an immunosuppressive agent, is undergoing clinical trials in the prophylaxis of organ rejection. OBJECTIVES: The aim of this study was to compare the performance of the semi-automated prototype (mode IA) microparticle enzyme immunoassay (MEIA) against a validated high-performance liquid chromatography-mass spectrometry (HPLC-MS) method for measuring sirolimus concentrations. A secondary objective was to identify potential factors that may influence sirolimus measurement. METHODS: The comparison was based on predose samples (n = 841) from 74 renal transplant patients receiving sirolimus therapy. Samples were collected up to 12 months after transplantation. RESULTS: The mean (+/- SD) overestimation by MEIA was 42.5%+/-16.9%. Several variables were investigated to determine potential contributors to the observed overestimation. Stratification of the data based on the mean sirolimus concentrations determined by both assays yielded no statistically significant differences in bias between concentration subgroups within the clinically relevant range. Multiple linear regression analysis identified HPLC-MS sirolimus concentration (P = 0.03), hemoglobin concentration (P < 0.001), and time after transplantation (P < 0.001) as significant variables in the prediction of overestimation by MEIA. Analysis of the effect of time after transplantation on overestimation yielded a statistically significant difference up to 6 months after transplantation (35.6% to 46.4%) compared with 9 (23.9%) and 12 months (24.4%). A relationship between hemoglobin concentration and time after transplantation may explain the reduction in bias observed after 6 months. CONCLUSION: The MEIA overestimates sirolimus concentrations in renal transplant patients compared with HPLC-MS. The clinical importance of this observed overestimation requires further investigation.

Autoanalysis↗
PubMed2000

Stability of sirolimus (rapamycin) in whole blood.

The effects of storage time (0-8 days), temperature (4 degrees C and 30 degrees C in dark and light), and freeze-thaw cycles on the stability of sirolimus in blood were examined. Sirolimus quantification was undertaken using HPLC-electrospray-tandem mass spectrometry. Whole blood samples supplemented with sirolimus (5.0, 15.0, and 30.0 microg/L) and pooled renal and heart transplant samples were found to be stable during the 8 days under all conditions (<10% decrease in concentration). No significant difference was observed in sirolimus concentration between freshly collected patient samples and sirolimus-supplemented samples (5.0, 15.0, and 30.0 microg/L) after three freeze-thaw cycles (p > 0.198). In conclusion, blood samples can be transported with or without cooling for up to 8 days without sirolimus results being compromised. The reanalysis of sirolimus samples, which may entail freeze-thaw cycles, can be undertaken if the number of cycles is three or less.

Drug Stability↗
PubMed2000

Evaluation of limited sampling strategies for estimation of 12-hour mycophenolic acid area under the plasma concentration-time curve in adult renal transplant patients.

Mycophenolate mofetil, the oral prodrug of mycophenolic acid, is indicated as immunosuppressive therapy after renal transplantation. To aid in the investigation of pharmacokinetic-pharmacodynamic relationships of mycophenolic acid in the clinical setting, limited blood sampling strategies have been proposed, and models from these developed, for the estimation of mycophenolic acid area under the concentration-time curve (AUC). In the current study, the authors investigated the predictive performance of six published models to estimate AUC. A total of 49 profiles from 25 renal transplant patients were used to test each model's performance against a full 14 time-point AUC. A wide range of agreement was found when predicted AUCs were compared with full AUCs using linear regression analysis (range: r2 = 0.499 to 0.836). Model 1, which uses 4 time-points over 6 hours, was found to be superior to all other models. The range of time-points used in this model takes into account patients with variable absorption. This model should be further tested on data sets from other centers. The relatively poor performance of the other models may be caused by their inability to describe the peak concentration in these patients. Caution is warranted when using limited sampling strategies on patients whose absorption of mycophenolic acid is altered, compared with those of the pharmacokinetic profiles from which the model was developed.

Adult↗
PubMed2000

Simultaneous quantification of tacrolimus and sirolimus, in human blood, by high-performance liquid chromatography-tandem mass spectrometry.

In this paper the authors present a validated method for the simultaneous analysis of tacrolimus and sirolimus in human blood by high-performance liquid chromatography-electrospray tandem mass spectrometry. Blood samples (500 microL) were prepared by C18 solid-phase extraction. Mass spectrometric detection was by selected reaction monitoring. The assay was linear for both compounds over the range 0.25-100 microg/L (r2 > 0.996, n = 7). At the limit of quantification (0.25 microg/L), for both sirolimus and tacrolimus, the interday imprecision was < 3% and the analytical recovery was between 97.0% and 102%, respectively. The interbatch and intrabatch coefficients of variation of the method for both analytes, at the three quality control concentrations (0.5, 20, and 80 microg/L), were < 16% and < 10%, respectively. The analytical recovery, at the three control concentrations, ranged from 99.2% to 104% of the nominal concentration. The mean absolute recovery (+/- standard deviation) of tacrolimus, sirolimus, and internal standard was 82 +/- 7%, 89 +/- 12%, and 77 +/- 8%, respectively (n = 12). In conclusion, the method presented can be used for simultaneous determination of tacrolimus and sirolimus and will aid in pharmacokinetic studies and therapeutic drug monitoring of these drugs. Furthermore, this method has economic benefits in the clinical setting where these drugs are coadministered.

Chromatography, High Pressure Liquid↗
PubMed1997

High-performance liquid chromatography-tandem mass spectrometry as a reference for analysis of tacrolimus to assess two immunoassays in patients with liver and renal transplants.

The accuracy and imprecision of three assays used for therapeutic monitoring of tacrolimus were tested using blood-containing weighed-in amounts of the drug, an enzyme-linked immunosorbent assay (ELISA), a microparticle enzyme immunoassay (MEIA I), and a high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS2) assay. Accuracy was acceptable for the HPLC-MS2 assay at all concentrations tested (< 10% deviation) and for the ELISA at 1.0 and 4.0 microg/l. Accuracy was not acceptable for the ELISA at 15.0 and 50.0 microg/l or for the MEIA I at all concentrations tested. Imprecision was acceptable for the HPLC-MS2 assay at all concentrations tested (coefficient of variation < 10%), for the ELISA at 15.0 and 50.0 microg/l, and for the MEIA I at 15.0 and 50.0 microg/l. Imprecision was not acceptable for the ELISA at 1.0 and 4.0 microg/l or for the MEIA I at 1.0 and 4.0 microg/l. This assessment with weighed-in amounts of tacrolimus verified the HPLC-MS2 assay as a reference method. The performance of the two immunoassays with HPLC-MS2 was then compared in the clinical setting using blood from patients with liver (n = 30) and renal (n = 37) transplants. In the liver transplant group (127 samples), the range of tacrolimus concentrations measured by HPLC-MS2, ELISA, and MEIA I was 1.9 to 31.8, 2.1 to 35.0, and less than 0.1 to 36.5 mg/l, respectively. In the renal transplant group (129 samples), the ranges were 1.7 to 26.1, 1.9 to 24.4, and 0.9 to 28.5 microg/l, respectively. Compared with the HPLC-MS2, the ELISA had minimal bias (0.1 to 0.2 microg/l) but unacceptable variability in values (SD > 13%). The MEIA I had unacceptable bias (1.7-1.8 microg/l) and variability (SD > 23%). These data indicated that neither the ELISA nor MEIA I is interchangeable with HPLC-MS2. Moreover, in view of the current trend to reduce the therapeutic dose of tacrolimus, quantitative results using the MEIA I would not be obtainable during therapeutic drug monitoring in some patients in whom effective therapeutic concentrations can be less than 5.0 microg/l.

Chromatography, High Pressure Liquid↗
PubMed1994

Comparison of high-performance liquid chromatography and monoclonal fluorescence polarization immunoassay for the determination of whole-blood cyclosporin A in liver and heart transplant patients.

Conflicting conclusions have been drawn from comparisons of high-performance liquid chromatography (HPLC) and the Abbott Diagnostics monoclonal fluorescence polarization immunoassay (mFPIA) for cyclosporin. The aim of this study was to compare whole blood cyclosporin A (CsA) concentrations measured by both mFPIA and HPLC in liver and heart transplant patients. One hundred and twenty-four liver and 62 heart transplant patient samples were assayed by both methods. Assay imprecision for both methods during the studies was < 7% over the range 150-800 micrograms/L. At an HPLC-determined concentration of 100 micrograms/L, mFPIA overestimated CsA by 60% (liver) and 77% (heart). At 300 micrograms/L, the overestimation was 40% (liver) and 45% (heart). On this basis, the mFPIA is not interchangeable with HPLC.

Antibodies, Monoclonal↗
PubMed1993

A reliable high-performance liquid chromatography assay for high-throughput routine cyclosporin A monitoring in whole blood.

We report here a reliable high-performance liquid chromatography-ultraviolet assay for routine assay of cyclosporin A (CsA) in whole blood using solid-phase extraction. This assay is linear, between 20 and 2,000 micrograms/L, with correlation coefficients > 0.998 for five consecutive standard curves. All coefficients of variation (CV) were < 8% at CsA concentrations of 45, 480, and 1,800 micrograms/L, with the exception of the between-day CV at 45 micrograms/L, which was < 15%. The relative accuracy of the method is > 94% at 45, 480, and 1,800 micrograms/L. The mean recoveries for CsA and cyclosporin D (internal standard) were 38.2 +/- 4.8% (n = 45) and 40.1 +/- 6.7% (n = 45), respectively. This method has proven to be reliable and robust in a high-throughput therapeutic drug monitoring laboratory.

Chemistry, Clinical↗
PubMed1992

Measurement of dothiepin and its major metabolites in plasma by high-performance liquid chromatography.

This paper describes a reversed-phase high-performance liquid chromatographic method which will simultaneously measure dothiepin and its three major metabolites (northiaden, northiaden-S-oxide and dothiepin-S-oxide) in plasma using trimipramine as internal standard. Sample preparation involved a basic extraction using diethyl ether followed by an acid back-extraction. The method we report is linear over the range 50-1000 ng/ml (r = 0.999), for all analytes. Total imprecision is less than 11% (coefficient of variation) and accuracy is greater than 94% (n = 20). Recovery of analytes varied considerably from 51.7% for northiaden-S-oxide to 90.2% for dothiepin-S-oxide.

Chromatography, High Pressure Liquid↗