Publications by authors named "Nils T Vethe"

17 Publications

  • Page 1 of 1

The Question of Accuracy Versus Interlaboratory Agreement for Monitoring the Immunosuppressants Everolimus and Sirolimus.

Ther Drug Monit 2021 06;43(3):444-446

Department of Medical Biochemistry, Stavanger University Hospital, Stavanger.

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http://dx.doi.org/10.1097/FTD.0000000000000892DOI Listing
June 2021

Prednisolone and Prednisone Pharmacokinetics in Adult Renal Transplant Recipients.

Ther Drug Monit 2021 04;43(2):247-255

Departments of Pharmacology and.

Background: Prednisolone (PL) is a standard component of most immunosuppressive protocols after solid organ transplantation (Tx). Adverse effects are frequent and well known. The aim of this study was to characterize the pharmacokinetics (PKs) of PL and prednisone (PN), including cortisol (CL) and cortisone (CN) profiles, after PL treatment in renal Tx recipients in the early post-Tx phase.

Methods: This single-center, prospective, observational study included stable renal Tx recipients, >18 years of age, and in the early postengraftment phase. Blood samples were obtained predose and during a 24-hour dose interval [n = 26 samples per area under the curve (AUC0-24)], within the first 8 weeks post-Tx. PL, PN, CL, and CN concentrations were measured using high-performance liquid chromatography-tandem mass spectrometry.

Results: In renal Tx recipients (n = 28), our results indicated a relatively high PL exposure [median, range AUC0-24 = 3821 (2232-5382) mcg h/L], paralleled by strong suppression of endogenous CL profile, demonstrated by a low CL evening-to-morning ratio [median, range 11 (3-47)%]. A negative correlation (r = -0.83) between PL AUC0-24 and morning CL levels was observed. The best single PK variable to predict PL AUC0-24 was PL C6 (r2 = 0.82). An algorithm based on 3 PK sampling time points: trough, 2, and 4 hours after PL dosing, predicted PL AUC0-24 with a low percentage prediction error (PPE = 5.2 ± 1.5%) and a good correlation of determination (r2 = 0.91). PL AUC0-24 varied 3-fold among study participants, whereas CL AUC0-24 varied by 18-fold.

Conclusions: The large interindividual variability in both PL exposure and suppression of endogenous CL implies a possible role for therapeutic drug monitoring. An abbreviated profile within the first 4 hours after PL dosing provides a good prediction of PL exposure in renal Tx recipients. The strong negative correlation between PL AUC0-24 and morning CL levels suggests a possible surrogate marker for drug exposure for further evaluation.
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http://dx.doi.org/10.1097/FTD.0000000000000835DOI Listing
April 2021

Salting Out-Assisted Liquid-Liquid Extraction for Liquid Chromatography-Tandem Mass Spectrometry Measurement of Tacrolimus, Sirolimus, Everolimus, and Cyclosporine a in Whole Blood.

Ther Drug Monit 2020 10;42(5):695-701

Department of Medical Biochemistry, Stavanger University Hospital, Stavanger.

Background: Therapeutic drug monitoring of the immunosuppressants tacrolimus, sirolimus, everolimus, and cyclosporine A is effectively performed by analyzing whole-blood samples using liquid chromatography coupled with tandem mass spectrometry. Samples are usually prepared using simple protein precipitation (PPT) with methanol and zinc sulfate (ZnSO4). Significant sample dilution is necessary to obtain clean extracts but may increase the limit of quantification of the method. Salting out-assisted liquid-liquid extraction (SALLE) was explored as a novel sample preparation method for measuring these drugs in blood.

Method: SALLE, which simply consists of LLE with a water-miscible solvent where phase separation is achieved by adding salt, was used to analyze treated blood samples.

Results: SALLE allowed direct injection of a 5-µL extract from the upper solvent phase into a reversed phase LC column, which would not be feasible using standard LLE. Compared with PPT, SALLE provided better extraction efficiencies and more ion enhancement, resulting in limit of quantification of 0.4, 1.4, 0.06, and 0.4 ng/mL for tacrolimus, sirolimus, everolimus, and cyclosporine A, respectively. Full-method validation was performed, including a comparison of results with those of another laboratory. A ≤10% bias was observed for tacrolimus and cyclosporine A, whereas further investigation of that for sirolimus (-12%) and everolimus (-18%) revealed that it was caused by the different calibrators used.

Conclusions: This is the first report of the use of SALLE for the measurement of tacrolimus, sirolimus, everolimus, and cyclosporine A in whole blood. The advantages of SALLE over PPT and conventional LLE would make it an attractive sample preparation method for clinical laboratories.
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http://dx.doi.org/10.1097/FTD.0000000000000794DOI Listing
October 2020

Measuring Intracellular Concentrations of Calcineurin Inhibitors: Expert Consensus from the International Association of Therapeutic Drug Monitoring and Clinical Toxicology Expert Panel.

Ther Drug Monit 2020 10;42(5):665-670

Clinical Chemistry Department, Cliniques Universitaires St Luc, Université catholique de Louvain, LTAP, Brussels, Belgium.

Background: Therapeutic drug monitoring (TDM) of the 2 calcineurin inhibitors (CNIs), tacrolimus (TAC) and cyclosporin A, has resulted in improvements in the management of patients who have undergone solid organ transplantation. As a result of TDM, acute rejection (AR) rates and treatment-related toxicities have been reduced. Irrespective, AR and toxicity still occur in patients who have undergone transplantation, showing blood CNI concentrations within the therapeutic range. Moreover, the AR rate is no longer decreasing. Hence, smarter TDM approaches are necessary. Because CNIs exert their action inside T lymphocytes, intracellular CNIs may be a promising candidate for improving therapeutic outcomes. The intracellular CNI concentration may be more directly related to the drug effect and has been favorably compared with the standard, whole-blood TDM for TAC in liver transplant recipients. However, measuring intracellular CNIs concentrations is not without pitfalls at both the preanalytical and analytical stages, and standardization seems essential in this area. To date, there are no guidelines for the TDM of intracellular CNI concentrations.

Methods: Under the auspices of the International Association of TDM and Clinical Toxicology and its Immunosuppressive Drug committees, a group of leading investigators in this field have shared experiences and have presented preanalytical and analytical recommendations for measuring intracellular CNI concentrations.
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http://dx.doi.org/10.1097/FTD.0000000000000780DOI Listing
October 2020

Tacrolimus Can Be Reliably Measured With Volumetric Absorptive Capillary Microsampling Throughout the Dose Interval in Renal Transplant Recipients.

Ther Drug Monit 2019 10;41(5):607-614

Departments of Pharmacology and.

Background: Therapeutic drug monitoring is standard practice for the immunosuppressant tacrolimus (Tac). Venous blood sampling at outpatient clinics is time-consuming and impractical with regard to obtaining trough concentrations on clinical visit days. Home-based blood sampling may be patient friendly and pave the way for limited sampling strategies for the prediction of total drug exposure. The aim was to establish a Tac assay for dried capillary microsamples, ensuring reliable measurements during the full dose interval in renal transplant recipients.

Methods: An assay based on volumetric absorptive microsampling and liquid chromatography tandem mass spectrometry was validated. The agreement between capillary microsamples and liquid venous samples was investigated in stable renal recipients on twice-daily Tac dosing. Sampling throughout the 12-hour dose interval was examined at 2 separate days, at least 1 week apart, for each participant. Two sets of samples were obtained at each time point, one delivered directly to the laboratory and one sent through mail.

Results: Twenty-seven renal transplant recipients were included, of whom 26 were investigated twice. Tac was efficiently extracted from the dried microsamples (mean recovery 94%-103%). The between-series mean accuracy was 88%-98% with coefficients of variation ≤5.0% (≤11% at the lower limit of quantification), measurement range 0.70-60 mcg/L. The mean difference between parallel microsamples was 5%-7%. Overall, the mean differences between dried microsamples and liquid samples were -3.1% when mailed (n = 679) and -4.2% when directly delivered (n = 682). Less than 8% were outside ±20%. The microsamples were stable for 1 month at ambient temperature.

Conclusions: The microsample method demonstrated acceptable performance. Tac concentrations can be reliably quantified throughout the dose interval by using volumetric absorptive microsampling in renal transplant recipients, and the results are not influenced by postal shipment.
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http://dx.doi.org/10.1097/FTD.0000000000000655DOI Listing
October 2019

A novel direct method to determine adherence to atorvastatin therapy in patients with coronary heart disease.

Br J Clin Pharmacol 2019 12 3;85(12):2878-2885. Epub 2019 Nov 3.

Department of Medicine, Vestre Viken Trust, Drammen Hospital, Drammen, Norway.

Aims: Objective methods to monitor statin adherence are needed. We have established a liquid chromatography-tandem mass spectrometry assay for quantification of atorvastatin and its metabolites in blood. This study aimed to develop an objective drug exposure variable with cut-off values to discriminate among adherence, partial adherence and nonadherence to atorvastatin therapy in patients with coronary heart disease.

Methods: Twenty-five patients treated with atorvastatin 10 mg (n = 5), 20 mg (n = 6), 40 mg (n = 7) and 80 mg (n = 7) participated in a directly observed atorvastatin therapy study to confirm baseline adherence. After the directly observed therapy, half of the patients (test group) were instructed to stop taking atorvastatin and return for blood sample collection the subsequent 3 days. Levels of atorvastatin and metabolites were compared between the test group and the adherent control group.

Results: The sum of parent drug and all measured primary metabolites correlated well with the atorvastatin dose administered (Spearman's rho = 0.71, 95% CI 0.44-0.87). The dose-normalized atorvastatin plus metabolites concentrations completely separated the partially adherent test group from the controls at 0.18 nM/mg after 3 days without atorvastatin. To reduce the risk of misinterpreting adherent patients as partially adherent, a corresponding cut-off at 0.10 nM/mg is proposed. A metabolite level of 2-OH atorvastatin acid <0.014 nmol/L provided the optimal cut-off for nonadherence.

Conclusion: A direct method to discriminate among adherence, partial adherence and nonadherence to atorvastatin therapy in patients with coronary heart disease has been developed. This tool may be important for novel studies on adherence and potentially useful in clinical practice.
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http://dx.doi.org/10.1111/bcp.14122DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6955401PMC
December 2019

Tacrolimus Area Under the Concentration Versus Time Curve Monitoring, Using Home-Based Volumetric Absorptive Capillary Microsampling.

Ther Drug Monit 2020 06;42(3):407-414

Department of Transplantation Medicine, Oslo University Hospital.

Background: Therapeutic drug monitoring (TDM) of tacrolimus (Tac) is mandatory in renal transplant recipients (RTxR). Area under the concentration versus time curve (AUC) is the preferred measure for Tac exposure; however, for practical purposes, most centers use trough concentrations as a clinical surrogate. Limited sampling strategies in combination with population pharmacokinetic model-derived Bayesian estimators (popPK-BE) may accurately predict individual AUC. The use of self-collected capillary microsamples could simplify this strategy. This study aimed to investigate the potential of AUC-targeted Tac TDM using capillary microsamples in combination with popPK-BE.

Methods: A single-center prospective pharmacokinetic study was conducted in standard-risk RTxR (n = 27) receiving Tac twice daily. Both venous and capillary microsamples (Mitra; Neoteryx, Torrance, CA) were obtained across 2 separate 12-hour Tac dosing intervals (n = 13 samples/AUC). Using popPK-BE, reference AUC (AUCref) was determined for each patient using all venous samples. Different limited sampling strategies were tested for AUC predictions: (1) the empiric sampling scheme; 0, 1, and 3 hours after dose and (2) 3 sampling times determined by the multiple model optimal sampling time function in Pmetrics. Agreement between the predicted AUCs and AUCref were evaluated using C-statistics. Accepted agreement was defined as a total deviation index ≤±15%.

Results: The AUC from capillary microsamples revealed high accuracy and precision compared with venous AUCref, and 85% of the AUCs had an error within ±11.9%. Applying microsamples at 0, 1, and 3 hours after dose predicted venous AUCref with acceptable agreement. Patients performed self-sampling with acceptable accuracy.

Conclusions: Capillary microsampling is patient-centered, making AUC-targeted TDM of Tac feasible without extended hospital stays. Samples obtained 0, 1, and 3 hours after dose, combined with popPK-BE, accurately predict venous Tac AUC.
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http://dx.doi.org/10.1097/FTD.0000000000000697DOI Listing
June 2020

Determination of Tacrolimus Concentration and Protein Expression of P-Glycoprotein in Single Human Renal Core Biopsies.

Ther Drug Monit 2018 06;40(3):292-300

Department of Pharmaceutical Biosciences, School of Pharmacy, University of Oslo, Oslo.

Background: Tacrolimus (TAC) is currently the cornerstone of immunosuppressive protocols for renal transplant recipients. Despite therapeutic whole blood monitoring, TAC is associated with nephrotoxicity, and it has been hypothesized that intrarenal accumulation of TAC and/or its metabolites are involved. As TAC is a substrate of P-glycoprotein (P-gp), the expression and activity of this efflux transporter could influence the levels of TAC in renal tissue. The primary aim of this study was to develop and validate a method for quantification of TAC in tissue homogenates from single human renal core biopsies. The secondary aim was to provide measures of P-gp expression and of the demethylated metabolites of TAC in the same renal biopsy.

Methods: Human renal tissue, with and without clinical TAC exposure, was used for method development and validation. Homogenates were prepared with bead-beating, and concentrations of TAC and its demethylated metabolites were analyzed with liquid chromatography tandem mass spectrometry after protein precipitation. A Western blot method was used for semiquantification of P-gp expression in the homogenates. The final methods were applied to renal core biopsies from 2 transplant patients.

Results: The TAC assay showed within- and between-run mean accuracy between 99.7% and 107% and coefficients of variation ≤6.7%. Matrix effects were nonsignificant, and samples were stable for 3 months preanalytically when stored at -80°C. TAC concentrations in the renal core biopsies were 62.6 and 43.7 pg/mg tissue. The methods for measurement of desmethyl-TAC and P-gp expression were suitable for semiquantification in homogenates from renal core biopsies.

Conclusions: These methods may be valuable for the elucidation of the pharmacokinetic mechanisms behind TAC-induced nephrotoxicity in renal transplant recipients.
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http://dx.doi.org/10.1097/FTD.0000000000000510DOI Listing
June 2018

NFAT-regulated cytokine gene expression during tacrolimus therapy early after renal transplantation.

Br J Clin Pharmacol 2017 Nov 16;83(11):2494-2502. Epub 2017 Aug 16.

Deptartment of Pharmacology, Oslo University Hospital, Oslo, Norway.

Aims: Despite pharmacokinetic monitoring of calcineurin inhibitors, the long-term outcome after transplantation (Tx) is still hampered by the side effects of these drugs. The aim of the present study was to characterize nuclear factor of activated T cells (NFAT)-regulated gene expression as a potential pharmacodynamic biomarker for further individualization of tacrolimus (Tac) therapy.

Methods: In 29 renal allograft recipients, samples were drawn once pre-Tx, and before and 1.5 h after Tac dosing at approximately 1 week, 6 weeks and 1 year post-Tx. Tac concentrations were measured by immunoassay, while the expression of genes encoding NFAT-regulated cytokines [interleukin 2 (IL2), interferon gamma (IFNG), colony stimulating factor 2 (CSF2)] and cytochrome P450 3A5 (CYP3A5) genotyping were determined by real-time polymerase chain reaction.

Results: The cytokine response after Tac dosing varied up to 46-fold between patients and changed significantly with time post-engraftment. Tac concentrations 1.5 h postdose (C ) >15 μg l were associated with strong cytokine inhibition and residual gene expression (RGE) ≤10%, while lower Tac C resulted in more variable responses (RGE 2.5-68.7%). Patients with ongoing subclinical acute rejection (n = 5) demonstrated limited cytokine inhibition (RGE 39.7-72.6%), while patients with polyoma virus viraemia (n = 3) had relatively strong inhibition of cytokines (RGE 2.5-32.5%). By contrast, there was no association between Tac exposure and rejection or viraemia.

Conclusions: The findings of our study support the potential of NFAT-regulated gene expression measurements as a pharmacodynamic tool for additional monitoring of Tac therapy, especially in the context of overimmunosuppression and viraemia.
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http://dx.doi.org/10.1111/bcp.13367DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5651309PMC
November 2017

Tacrolimus exposure and mycophenolate pharmacokinetics and pharmacodynamics early after liver transplantation.

Ther Drug Monit 2014 Feb;36(1):46-53

*Department of Medical Biochemistry, Oslo University Hospital; †Department of Pharmaceutical Biosciences, School of Pharmacy, University of Oslo; Departments of ‡Transplantation Medicine; and §Pharmacology, Oslo University Hospital, Oslo, Norway.

Background: Mycophenolic acid (MPA) and tacrolimus play important roles in immunosuppressive therapy after solid organ transplantation (Tx) and show large intra- and interindividual pharmacokinetic (PK) variabilities. The purpose of this study was to describe the intra- and interindividual variabilities of MPA and tacrolimus PKs during the first 3 weeks after adult liver transplantation. Furthermore, inosine monophosphate dehydrogenase activity was investigated.

Materials: This study describes PK and pharmacodynamic parameters of MPA and the PKs of tacrolimus in 16 liver transplant recipients, in 4 follow-up periods (I-IV).

Results: The area under the concentration-time curve (AUC(0-12 hours)) for tacrolimus was low early after Tx (eg, median 78.6 around day 4) and variable in all 4 periods ranging from 3.8 to 267 μg h/L, whereas the predose concentrations (C₀) were 0.0-17.9 μg/L. From periods I to IV, the tacrolimus dose was doubled and the median dose per body weight-adjusted AUC(0-12 hours) increased by 123% (P = 0.017). The AUC(0-12 hours) of MPA was in the range 8.6-57.4 mg h/L, with median values from 21.9 to 27.8 mg h/L, whereas C₀ was between 0.0 and 7.3 mg/L in the 4 periods (medians from 1.2 to 1.6 mg/L). The maximum inhibition of inosine monophosphate dehydrogenase within a dose interval ranged from 9.5% to 100%.

Conclusions: This study confirmed the large variability in the PKs of tacrolimus and MPA in liver transplant recipients. In particular, the MPA AUC(0-12 hours) was consistently low in all 4 periods. We also observed a low tacrolimus exposure during the first days after transplant compared with the following weeks.
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http://dx.doi.org/10.1097/FTD.0b013e31829dcb66DOI Listing
February 2014

Mycophenolate pharmacokinetics and inosine monophosphate dehydrogenase activity in liver transplant recipients with an emphasis on therapeutic drug monitoring.

Scand J Clin Lab Invest 2013 Mar 3;73(2):117-24. Epub 2013 Jan 3.

Department of Anaesthesiology, Oslo University Hospital, Oslo, Norway.

Background: The pharmacokinetics of the immunosuppressant mycophenolic acid (MPA) demonstrates high inter- and intra-patient variability. Variation in the binding of MPA to albumin has been postulated to be an important factor in this variability, and monitoring of free MPA has been suggested to improve therapeutic drug monitoring (TDM) of MPA. Inosine monophosphate dehydrogenase (IMPDH) is the target enzyme for MPA, therefore the IMPDH activity in lymphocytes can serve as a marker of the MPA-specific response. This study aimed to explore how the albumin concentration influences the free concentration of MPA in liver transplant recipients and to assess whether alteration in the free MPA influences IMPDH activity in CD4 + cells.

Methods: Blood samples were taken from 20 liver transplant recipients on two separate occasions (days 3-5 and 16-21). Total and free concentrations of MPA, and IMPDH activity were measured during the first 4 h of each dose interval.

Results: Albumin levels correlated with the free fraction of MPA. However, the total MPA and free MPA were equal predictors of the immunosuppressive response as defined by IMPDH activity.

Conclusion: Total and free MPA are equally good predictors of the immunosuppressive effect exerted by MPA as defined by IMPDH activity. IMPDH activity measurements represent a promising approach to TDM in patients treated with MPA.
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http://dx.doi.org/10.3109/00365513.2012.745947DOI Listing
March 2013

Quantification of 6 glucocorticoids in human plasma by liquid chromatography tandem mass spectrometry: method development, validation, and assessment of matrix effects.

Ther Drug Monit 2011 Aug;33(4):402-10

Department of Medical Biochemistry, Oslo University Hospital, Oslo, Norway.

Background: Glucocorticoids are a group of steroid hormones with immunosuppressive and anti-inflammatory properties. In this article, we report the development and the validation of a liquid chromatography tandem mass spectrometry method for the simultaneous quantification of prednisolone, prednisone, cortisol, cortisone, methylprednisolone, and dexamethasone in human plasma. Furthermore, matrix effects were assessed qualitatively and quantitatively.

Methods: Plasma protein precipitation was performed with acetonitrile containing internal standards. Liquid-liquid extraction with dichloromethane and evaporation were used for cleanup and enrichment. The glucocorticoids were analyzed using reversed-phase chromatography and multiple reaction monitoring of positive ions.

Results: The mean extraction recovery was in the range 66.5%-104.8%, whereas the lower limits of quantification ranged from 1.5 to 4.0 μg/L. The intraday and interday accuracies of all the analytes were within 89.4%-116.6%, and imprecision was <15.6%. Ion suppression ranged from 15.3% to 27.3%. However, the matrix effects did not compromise the assay performance, with mean deviations in calculated concentrations of -4.8% to 2.1% between methanol and matrix. Short-term stability was acceptable for 5 of the analytes, with deviations from baseline between -3.4% and 8.7% after 24 hours at 4°C, although methylprednisolone was stable for 6 hours with a degradation of 10.2%. Deviations from baseline in controls stored at -20°C for 6 months ranged from -22.3% to 6.3%. All analytes were stable after 3 repetitive freeze-thaw cycles, with a maximum degradation of 5.5%. In terms of postpreparative stability, the analytes were stable after 24 and 48 hours at 4°C, with maximum degradation of 6.1% and 9.4%, respectively.

Conclusions: A validated, sensitive, selective, and reproducible method for quantifying the concentrations of 6 glucocorticoids in human plasma by liquid chromatography tandem mass spectrometry is reported.
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http://dx.doi.org/10.1097/FTD.0b013e3182241799DOI Listing
August 2011

Determination of cyclosporine, tacrolimus, sirolimus and everolimus by liquid chromatography coupled to electrospray ionization and tandem mass spectrometry: assessment of matrix effects and assay performance.

Scand J Clin Lab Invest 2010 Dec 1;70(8):583-91. Epub 2010 Nov 1.

Department of Medical Biochemistry, Oslo University Hospital, Rikshospitalet,, Oslo, Norway.

Objective: The immunosuppressants cyclosporine, tacrolimus, sirolimus and everolimus are used in rejection prophylaxis after transplantation. Liquid chromatography tandem mass spectrometry (LC-MS/MS) has become a widely used methodology for monitoring of the drug levels to ensure therapeutic exposure. The main objective of the study was to evaluate the existence and potential influence of matrix effects on LC-MS/MS measurements of the immunosuppressants in clinical blood samples.

Methods: The samples were prepared by protein precipitation and thereafter analysed by reversed-phase chromatography coupled to MS/MS via an electrospray interface. Assay performance including within- and between-series imprecision and deviations from external controls were examined. Elution of overall matrix components and glycerophosphocholines were investigated. The MS/MS signals were monitored in post-column infusion experiments, and post-precipitation addition of compounds provided a basis for quantification of the matrix effects. The influence of matrix effects on assay performance was investigated after dilution of quality controls with blood from multiple individuals.

Results: Between-series coefficients of variation were ≤ 5.1, ≤ 6.6, ≤ 11.0 and ≤ 7.4 %, and the mean deviations from external controls were -10.3, -6.7, 15.6 and 4.3% for cyclosporine, tacrolimus, sirolimus and everolimus, respectively. The elution of matrix components including glycerophosphocholines overlapped to some extent with the target compounds, and the average ion suppression ranged from 8.5-21%. However, the drugs and internal standards were correspondingly influenced.

Conclusion: The internal standards consistently corrected the between-individual variability of matrix effects. These findings consolidate the reliability of the assay.
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http://dx.doi.org/10.3109/00365513.2010.531141DOI Listing
December 2010

Mycophenolate pharmacokinetics and pharmacodynamics in belatacept treated renal allograft recipients - a pilot study.

J Transl Med 2009 Jul 27;7:64. Epub 2009 Jul 27.

Department of Medical Biochemistry, Rikshospitalet University Hospital, Oslo, Norway.

Background: Mycophenolic acid (MPA) is widely used as part of immunosuppressive regimens following allograft transplantation. The large pharmacokinetic (PK) and pharmacodynamic (PD) variability and narrow therapeutic range of MPA provide a potential for therapeutic drug monitoring. The objective of this pilot study was to investigate the MPA PK and PD relation in combination with belatacept (2nd generation CTLA4-Ig) or cyclosporine (CsA).

Methods: Seven renal allograft recipients were randomized to either belatacept (n = 4) or cyclosporine (n = 3) based immunosuppression. Samples for MPA PK and PD evaluations were collected predose and at 1, 2 and 13 weeks posttransplant. Plasma concentrations of MPA were determined by HPLC-UV. Activity of inosine monophosphate dehydrogenase (IMPDH) and the expressions of two IMPDH isoforms were measured in CD4+ cells by HPLC-UV and real-time reverse-transcription PCR, respectively. Subsets of T cells were characterized by flow cytometry.

Results: The MPA exposure tended to be higher among belatacept patients than in CsA patients at week 1 (P = 0.057). Further, MPA concentrations (AUC0-9 h and C0) increased with time in both groups and were higher at week 13 than at week 2 (P = 0.031, n = 6). In contrast to the postdose reductions of IMPDH activity observed early posttransplant, IMPDH activity within both treatment groups was elevated throughout the dosing interval at week 13. Transient postdose increments were also observed for IMPDH1 expression, starting at week 1. Higher MPA exposure was associated with larger elevations of IMPDH1 (r = 0.81, P = 0.023, n = 7 for MPA and IMPDH1 AUC0-9 h at week 1). The maximum IMPDH1 expression was 52 (13-177)% higher at week 13 compared to week 1 (P = 0.031, n = 6). One patient showed lower MPA exposure with time and did neither display elevations of IMPDH activity nor IMPDH1 expression. No difference was observed in T cell subsets between treatment groups.

Conclusion: The significant influence of MPA on IMPDH1 expression, possibly mediated through reduced guanine nucleotide levels, could explain the elevations of IMPDH activity within dosing intervals at week 13. The present regulation of IMPDH in CD4+ cells should be considered when interpreting measurements of IMPDH inhibition.
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http://dx.doi.org/10.1186/1479-5876-7-64DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2724496PMC
July 2009

Rimonabant affects cyclosporine a, but not tacrolimus pharmacokinetics in renal transplant recipients.

Transplantation 2009 Apr;87(8):1221-4

Department of Pharmaceutical Biosciences, School of Pharmacy, University of Oslo, Oslo, Norway.

Background: Obesity is a common problem following renal transplantation. Rimonabant, a cannabinoid-1 receptor blocker, offers a new approach for reducing obesity.

Methods: The potential pharmacokinetic interaction between rimonabant and cyclosporine A (CsA, n=10) and tacrolimus (Tac, n=8) was assessed in stable renal transplant recipients 6.2 (0.9-21.7) years posttransplant. A 12-hour pharmacokinetic profile was obtained before and after two months of concomitant treatment with 20 mg rimonabant each morning.

Results: Rimonabant treatment induced a moderate, but significant increase in CsA AUC0-12 (19.8+/-16.1 %, P=0.005). Cmax and C2 values tended to increase whereas C0 remained unaffected. Tac pharmacokinetics was not significantly affected by rimonabant treatment. Eleven of 18 patients experienced adverse events. Two patients reported depressions and one reported severe nightmares.

Conclusions: The effect on CsA pharmacokinetics is probably of marginal clinical relevance since trough concentrations were unaltered, but CsA concentrations should probably be more closely monitored if rimonabant treatment is initiated, preferably by C2 monitoring.
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http://dx.doi.org/10.1097/TP.0b013e31819f1001DOI Listing
April 2009

Expression of IMPDH1 is regulated in response to mycophenolate concentration.

Int Immunopharmacol 2009 Feb 20;9(2):173-80. Epub 2008 Nov 20.

Department of Medical Biochemistry, Rikshospitalet University Hospital, Oslo, Norway.

Inosine 5'-monophosphate dehydrogenase (IMPDH) catalyzes de novo guanine nucleotide synthesis. Mycophenolic acid (MPA) exerts immunosuppressive effects by inhibiting IMPDH. The aim of this study was to investigate gene expressions of two IMPDH isoforms, during in vivo exposure to MPA. Healthy volunteers (n=5) were given single doses of 100, 250, 500 and 1000 mg mycophenolate mofetil (MMF). Blood was sampled pre-dose and at 1, 2, 4, 6, 8, 12, and 24 h post-dose. The expressions of IMPDH 1 and 2 were quantified in CD4+ cells and whole blood by real-time reverse transcription-PCR. Following MMF doses of 500 mg, the expression of IMPDH 1 and 2 in CD4+ cells was reduced 39% (P=0.043) and 10% (P=0.043), respectively. Smaller reductions (ns) were observed after 1000 mg MMF. Similar trends were demonstrated for whole blood. The largest reductions of IMPDH1 occurred at MPA AUC(0-12 h) of 20 mg h/L. Below this, increasing MPA exposure correlated with larger reductions of IMPDH1 expression (CD4+ cells: r=-0.82, P<0.001, and whole blood: r=-0.50, P=0.04, n=17), while higher MPA exposure seemed to be associated with smaller reductions of expression (CD4+ cells: r=0.42, ns, and whole blood: r=0.77, P=0.039, n=8). The concentration-dependent modulation of IMPDH 1 and 2 expressions by MPA might impact IMPDH activity. Knowledge of the regulation of the two IMPDH isoenzymes in vivo by MPA is of importance considering pharmacodynamic monitoring and optimization of MPA treatment.
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http://dx.doi.org/10.1016/j.intimp.2008.10.017DOI Listing
February 2009

Expression of IMPDH1 and IMPDH2 after transplantation and initiation of immunosuppression.

Transplantation 2008 Jan;85(1):55-61

Department of Medical Biochemistry, Rikshospitalet Medical Centre, Institute of Clinical Biochemistry, University of Oslo, Norway.

Background: Mycophenolic acid (MPA) mediates immunosuppressive effects by inhibiting inosine monophosphate dehydrogenase (IMPDH). Induction of IMPDH activity has been observed in whole blood and erythrocyte samples during immunosuppressive therapy. Information concerning the mechanisms for increased IMPDH activity is limited and the potential implications of induction have been debated.

Methods: Whole blood, CD4+ cell, and reticulocyte samples were collected from 30 renal transplant patients pre- and posttransplantation. The expressions of two IMPDH isoforms, type 1 and 2, were analyzed by real-time reverse-transcription polymerase chain reaction and quantified using a housekeeping gene index. The IMPDH activity was determined by ultraviolet high-performance liquid chromatography.

Results: Transplantation and the initiation of immunosuppressive therapy was associated with increased IMPDH1 (50-88%, P<0.0005) and decreased IMPDH2 (42-56%, P<0.0005) expression. In CD4+ cells, however, IMPDH2 increased (15%, P=0.009). These changes are probably related to glucocorticoid effects. Two weeks posttransplant, MPA-treated patients displayed elevated IMPDH 1 and 2 in reticulocytes, suggesting enzyme induction in these cells during prolonged MPA therapy. Patients with acute rejection during follow-up demonstrated higher IMPDH2 expression in CD4+ cells pretransplant than nonrejecting patients (median expression 1.26 vs. 0.87 respectively, P=0.017).

Conclusions: Knowledge of changes in IMPDH 1 and 2 expression after transplantation and initiation of immunosuppression is important considering the action of MPA on IMPDH and the potential for pharmacodynamic monitoring of MPA by measuring IMPDH activity. The expression of IMPDH2 in CD4+ cells pretransplant may be an indicator of immune activation.
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http://dx.doi.org/10.1097/01.tp.0000296854.68123.03DOI Listing
January 2008