Establishment of high-performance liquid chromatography and enzyme multiplied immunoassay technology methods for determination of free mycophenolic acid and its application in Chinese liver transplant recipients. Ther Drug Monit. 2010;32:653-660. [PMID: 20814351 DOI: 10.1097/ftd.0b013e3181f01397]

Quantification of mycophenolic acid in plasma by isotope dilution liquid chromatography-tandem mass spectrometry candidate reference method

Accurate measurements of plasma mycophenolic acid (MPA) are essential for therapeutic drug monitoring in transplant recipients and autoimmune diseases. The performance of plasma mycophenolic acid routine methods remains highly variable that calls for a candidate reference measurement procedure (cRMP) to improve the standardization of plasma mycophenolic acid measurements. In this study, sample preparation was based on protein precipitation with methanol followed by further dilution. The mycophenolic acid was quantified by the isotope dilution liquid chromatography-tandem mass spectrometry (ID-LC-MS/MS) with electrospray ionization in positive ion mode. According to the Clinical and Laboratory Standards Institute (CLSI) documents C62-A and C50-A, the basic analytical performance of the candidate reference method was verified, such as linearity, limit of quantification, matrix effect, precision, accuracy, and uncertainty. Moreover, the candidate reference measurement procedure was compared with the routine liquid chromatography-tandem mass spectrometry (LC-MS/MS) method in a clinical laboratory. Based on the data, the mycophenolic acid in human plasma was well detected by ID-LC-MS/MS. No apparent interferences were found with the mycophenolic acid measurement. The calibration curve for the mycophenolic acid was linear in the concentration range of 0.1-50 μg/mL with a correlation coefficient of 0.9999 under the optimum experimental conditions. This method was sensitive because the low limit of quantitation (LOQ) was 0.05 μg/mL. The recoveries of MPA were 98.11-98.95%. The intra-day and inter-day coefficients of variations (CV) of our method were ≤ 1.53% and ≤ 0.51%, respectively. No obvious matrix effect was observed. There was a good correlation between this method and the clinical routine LC-MS/MS method. To sum up, we established and validated a reliable plasma MPA method using ID-LC/MS/MS. The desirable accuracy and precision of this method enable it to serve as a promising cRMP to improve the standardization for plasma MPA routine measurements.

Ultrahigh-sensitivity multi-parameter tacrolimus solution detection based on an anchor planar millifluidic microwave biosensor

To detect drug concentration in tacrolimus solution, an anchor planar millifluidic microwave (APMM) biosensor is proposed. The millifluidic system integrated with the sensor enables accurate and efficient detection while eliminating interference caused by the fluidity of the tacrolimus sample. Different concentrations (10-500 ng mL^-1) of the tacrolimus analyte were introduced into the millifluidic channel, where it completely interacts with the radio frequency patch electromagnetic field, thereby effectively and sensitively modifying the resonant frequency and amplitude of the transmission coefficient. Experimental results indicate that the sensor has an extremely low limit of detection (LoD) of 0.12 pg mL^-1 and a frequency detection resolution (FDR) of 1.59 (MHz (ng mL^-1)). The greater the FDR and the lower the LoD, the more the feasibility of a label-free biosensing method. Regression analysis revealed a strong linear correlation (R² = 0.992) between the concentration of tacrolimus and the frequency difference of the two resonant peaks of APMM. In addition, the difference in the reflection coefficient between the two formants was measured and calculated, and a strong linear correlation (R² = 0.998) was found between the difference and tacrolimus concentration. Five measurements were performed on each individual sample of tacrolimus to validate the biosensor's high repeatability. Consequently, the proposed biosensor is a potential candidate for the early detection of tacrolimus drug concentration levels in organ transplant recipients. This study presents a simple method for constructing microwave biosensors with high sensitivity and rapid response.

腎移植患者におけるミコフェノール酸血中濃度に対する高速液体クロマトグラフLM1010の精度評価

Plasma concentrations of mycophenolic acid (MPA), an immunosuppressive agent, have been measured in clinical settings using immunoassay methods or HPLC. However, immunoassay methods show cross-reactivity with metabolites of MPA glucuronide. Recently, the LM1010 high-performance liquid chromatography instrument was approved as a new general medical device. In this study, we compared the results of MPA plasma concentrations analyzed using the LM1010 method and the previously described HPLC method. Plasma samples obtained from 100 renal transplant patients (32 women and 68 men) were evaluated using both HPLC instruments. Deming regression analyses showed a very high correlation between the two instruments, with a slope of 0.9892 and an intercept of 0.0235 µg/mL (r²=0.982). Bland-Altman analysis showed an average of -0.0012 µg/mL between the LM1010 method and the previously described HPLC method. For the LM1010 method, the total run time for MPA analysis was 7 min, and the analytical time was short; however, the extraction recovery when using a spin column was extremely low for frozen plasma samples stored at -20°C for 1 month, and the volume required for the assay (150 µL) could not be collected. Thus, for the LM1010 method, analysis using fresh plasma samples was optimal. Overall, our findings showed that the LM1010 method was a rapid, accurate HPLC assay for MPA analysis and could be used in clinical practice for routine monitoring of MPA in fresh plasma samples.

High-performance liquid chromatography with fluorescence detection for mycophenolic acid determination in saliva samples

BACKGROUND

For therapeutic drug monitoring (TDM) of mycophenolic acid (MPA), which is frequently proposed, saliva might be a suitable and easy-to-obtain biological matrix. The study aimed to validate an HPLC method with fluorescence detection for determining mycophenolic acid in saliva (sMPA) in children with nephrotic syndrome.

METHODS

The mobile phase was composed of methanol and tetrabutylammonium bromide with disodium hydrogen phosphate (pH 8.5) at a 48:52 ratio. To prepare the saliva samples, 100 µL of saliva, 50 µL of calibration standards, and 50 µL of levofloxacin (used as an internal standard) were mixed and evaporated to dryness at 45 °C for 2 h. The resulting dry extract was reconstituted in the mobile phase and injected into the HPLC system after centrifugation. Saliva samples from study participants were collected using Salivette^® devices.

RESULTS

The method was linear within the range of 5-2000 ng/mL, was selective with no carry-over effect and met the acceptance criteria for within-run and between-run accuracy and precision. Saliva samples can be stored for up to 2 h at room temperature, for up to 4 h at 4 °C, and for up to 6 months at - 80 °C. MPA was stable in saliva after three freeze-thaw cycles, in dry extract for 20 h at 4 °C, and for 4 h in the autosampler at room temperature. MPA recovery from Salivette^® cotton swabs was within the range of 94-105%. The sMPA concentrations in the two children with nephrotic syndrome who were treated with mycophenolate mofetil were within 5-112 ng/mL.

CONCLUSIONS

The sMPA determination method is specific, selective, and meets the validation requirements for analytic methods. It may be used in children with nephrotic syndrome; however further studies are required to investigate focusing on sMPA and the correlation between sMPA and total MPA and its possible contribution to MPA TDM is required.

Limited sampling strategy to predict free mycophenolic acid area under the concentration-time curve in paediatric patients with nephrotic syndrome

In paediatric patients, there is no data on the recommended area under the concentration-time curve from 0 to 12 h (AUC_0-12 ) for free mycophenolic acid (fMPA), which is the active form of the drug, responsible for the pharmacological effect. We decided to establish the limited sampling strategy (LSS) for fMPA for its use in MPA therapeutic monitoring in children with nephrotic syndrome treated with mycophenolate mofetil (MMF). This study included 23 children (aged 11 ± 4 years) from whom eight blood samples were collected within 12 h after MMF administration. The fMPA was determined using the high-performance liquid chromatography with fluorescence detection method. LSSs were estimated with the use of R software and bootstrap procedure. The best model was chosen based on a number of profiles with AUC predicted within ± 20% of AUC_0-12 (good guess), r² , mean prediction error (%MPE) of ±10% and mean absolute error (%MAE) of less than 25%. The fMPA AUC_0-12 was 0.1669 ± 0.0697 μg h/mL and the free fraction was within 0.16%-0.81%. In total, there were 92 equations developed of which five fulfilled the acceptance criteria for %MPE, %MAE, good guess >80% and r²  > 0.900. These equations consisted of three time points: model 1 (C₁ , C₂ , C₆ ), model 2 (C₁ , C₃ , C₆ ), model 3 (C₁ , C₄ , C₆ ), model 5 (C₀ , C₁ , C₂ ), and model 6 (C₁ , C₂ , C₉ ). Although blood sampling up to 9 h after MMF dosing is impractical, it is crucial to include C₆ or C₉ in LSS to assess fMPA AUC_pred correctly. The most practical fMPA LSS, which fulfilled the acceptance criteria in the estimation group, was fMPA AUC_pred  = 0.040 + 2.220 × C₀  + 1.130 × C₁  + 1.742 × C₂ . Further studies should define the recommended fMPA AUC_0-12 value in children with nephrotic syndrome.

An Overview of Analytical Methodologies for Determination of Vancomycin in Human Plasma

Vancomycin is regarded as the last resort of defense for a wide range of infections due to drug resistance and toxicity. The detection of vancomycin in plasma has always aroused particular concern because the performance of the assay affects the clinical treatment outcome. This article reviews various methods for vancomycin detection in human plasma and analyzes the advantages and disadvantages of each technique. Immunoassay has been the first choice for vancomycin concentration monitoring due to its simplicity and practicality, occasionally interfered with by other substances. Chromatographic methods have mainly been used for scientific research due to operational complexity and the particular requirement of the instrument. However, the advantages of a small amount of sample needed, high sensitivity, and specificity makes chromatography irreplaceable. Other methods are less commonly used in clinical applications because of the operational feasibility, clinical application, contamination, etc. Simplicity, good performance, economy, and environmental friendliness have been points of laboratory methodological concern. Unfortunately, no one method has met all of the elements so far.

A Systematic Review of Multiple Linear Regression-Based Limited Sampling Strategies for Mycophenolic Acid Area Under the Concentration-Time Curve Estimation

Background and Objective

One approach of therapeutic drug monitoring in the case of mycophenolic acid (MPA) is a limited sampling strategy (LSS), which allows the evaluation of the area under the concentration–time curve (AUC) based on few concentrations. The aim of this systematic review was to review the MPA LSSs and define the most frequent time points for MPA determination in patients with different indications for mycophenolate mofetil (MMF) administration.

Methods

The literature was comprehensively searched in July 2021 using PubMed, Scopus, and Medline databases. Original articles determining multiple linear regression (MLR)-based LSSs for MPA and its free form (fMPA) were included. Studies on enteric-coated mycophenolic sodium, previously established LSS, Bayesian estimator, and different than twice a day dosing were excluded. Data were analyzed separately for (1) adult renal transplant recipients, (2) adults with other than renal transplantation indication, and (3) for pediatric patients.

Results

A total of 27, 17, and 11 studies were found for groups 1, 2, and 3, respectively, and 126 MLR-based LSS formulae (n = 120 for MPA, n = 6 for fMPA) were included in the review. Three time-point equations were the most frequent. Four MPA LSSs: 2.8401 + 5.7435 × C0 + 0.2655 × C0.5 + 1.1546 × C1 + 2.8971 × C4 for adult renal transplant recipients, 1.783 + 1.248 × C1 + 0.888 × C2 + 8.027 × C4 for adults after islet transplantation, 0.10 + 11.15 × C0 + 0.42 × C1 + 2.80 × C2 for adults after heart transplantation, and 8.217 + 3.163 × C0 + 0.994 × C1 + 1.334 × C2 + 4.183 × C4 for pediatric renal transplant recipients, plus one fMPA LSS, 34.2 + 1.12 × C1 + 1.29 × C2 + 2.28 × C4 + 3.95 × C6 for adult liver transplant recipients, seemed to be the most promising and should be validated in independent patient groups before introduction into clinical practice. The LSSs for pediatric patients were few and not fully characterized. There were only a few fMPA LSSs although fMPA is a pharmacologically active form of the drug.

Conclusions

The review includes updated MPA LSSs, e.g., for different MPA formulations (suspension, dispersible tablets), generic form, and intravenous administration for adult and pediatric patients, and emphasizes the need of individual therapeutic approaches according to MMF indication. Five MLR-based MPA LSSs might be implemented into clinical practice after evaluation in independent groups of patients. Further studies are required, e.g., to establish fMPA LSS in pediatric patients.

The Evaluation of Multiple Linear Regression-Based Limited Sampling Strategies for Mycophenolic Acid in Children with Nephrotic Syndrome

We evaluated mycophenolic acid (MPA) limited sampling strategies (LSSs) established using multiple linear regression (MLR) in children with nephrotic syndrome treated with mycophenolate mofetil (MMF). MLR-LSS is an easy-to-determine approach of therapeutic drug monitoring (TDM). We assessed the practicability of different LSSs for the estimation of MPA exposure as well as the optimal time points for MPA TDM. The literature search returned 29 studies dated 1998–2020. We applied 53 LSSs (n = 48 for MPA, n = 5 for free MPA [fMPA]) to predict the area under the time-concentration curve (AUC_pred) in 24 children with nephrotic syndrome, for whom we previously determined MPA and fMPA concentrations, and compare the results with the determined AUC (AUC_total). Nine equations met the requirements for bias and precision ±15%. The MPA AUC in children with nephrotic syndrome was predicted the best by four time-point LSSs developed for renal transplant recipients. Out of five LSSs evaluated for fMPA, none fulfilled the ±15% criteria for bias and precision probably due to very high percentage of bound MPA (99.64%). MPA LSS for children with nephrotic syndrome should include blood samples collected 1 h, 2 h and near the second MPA maximum concentration. MPA concentrations determined with the high performance liquid chromatography after multiplying by 1.175 may be used in LSSs based on MPA concentrations determined with the immunoassay technique. MPA LSS may facilitate TDM in the case of MMF, however, more studies on fMPA LSS are required for children with nephrotic syndrome.

Personalized Therapy for Mycophenolate: Consensus Report by the International Association of Therapeutic Drug Monitoring and Clinical Toxicology

ABSTRACT

When mycophenolic acid (MPA) was originally marketed for immunosuppressive therapy, fixed doses were recommended by the manufacturer. Awareness of the potential for a more personalized dosing has led to development of methods to estimate MPA area under the curve based on the measurement of drug concentrations in only a few samples. This approach is feasible in the clinical routine and has proven successful in terms of correlation with outcome. However, the search for superior correlates has continued, and numerous studies in search of biomarkers that could better predict the perfect dosage for the individual patient have been published. As it was considered timely for an updated and comprehensive presentation of consensus on the status for personalized treatment with MPA, this report was prepared following an initiative from members of the International Association of Therapeutic Drug Monitoring and Clinical Toxicology (IATDMCT). Topics included are the criteria for analytics, methods to estimate exposure including pharmacometrics, the potential influence of pharmacogenetics, development of biomarkers, and the practical aspects of implementation of target concentration intervention. For selected topics with sufficient evidence, such as the application of limited sampling strategies for MPA area under the curve, graded recommendations on target ranges are presented. To provide a comprehensive review, this report also includes updates on the status of potential biomarkers including those which may be promising but with a low level of evidence. In view of the fact that there are very few new immunosuppressive drugs under development for the transplant field, it is likely that MPA will continue to be prescribed on a large scale in the upcoming years. Discontinuation of therapy due to adverse effects is relatively common, increasing the risk for late rejections, which may contribute to graft loss. Therefore, the continued search for innovative methods to better personalize MPA dosage is warranted.

Correlation between enzyme multiplied immunoassay technique and high-performance liquid chromatography in the quantification of voriconazole in a paediatric population

The enzyme multiplied immunoassay technique (EMIT) is a new method for determining the plasma concentration of voriconazole (VRZ). This study aimed to investigate the correlation between EMIT and high-performance liquid chromatography/ultraviolet rays (HPLC/UV) in determining the plasma VRZ trough concentration in children, in China. A total of 419 blood samples were collected, and plasma VRZ concentrations were detected by the EMIT and HPLC methods. The results of 304 samples were analysed after excluding samples that were undetectable or beyond the quantification limit. A test result value of 0 was defined as undetectable, while concentrations outside the detection range (0.2 - 20.0 μg/ml for HPLC and 0.5 - 16.0 µg/ml for EMIT) were defined as beyond the quantification limit. Results from both methods were compared using the Passing Bablok regression, Bland-Altman plot analysis, and paired Wilcoxon test. The plasma VRZ concentrations determined by EMIT and HPLC showed a strong linear correlation through the linear regression equation Y_EMIT = 1.310 × HPLC +0.149 (R² = 0.9082). The Bland-Altman plot analysis showed poor level consistency as measured by the two methods. The paired Wilcoxon-test showed a significant difference between the two methods (p < .0001). Compared to EMIT, HPLC accurately detected plasma VRZ concentration, making it suitable for VRZ therapeutic drug monitoring. The numerical values of the EMIT-measured levels were higher than those of HPLC, which may be related to VRZ metabolites interference and co-administrated drugs.

Pharmacokinetics of Enteric-Coated Mycophenolate Sodium Metabolites in Patients Over 60 Years Old Within the First Year After Renal Transplantation

OBJECTIVE

It is still unclear whether mycophenolic acid (MPA) doses should be adjusted for older patients. Therefore, we compared the pharmacokinetics of MPA, mycophenolic acid glucuronide (MPAG), and free MPA (fMPA) between older and younger renal transplant recipients.

METHODS

We included 12 patients <60 years and 6 patients >60 years within the first year after renal transplantation, who were receiving enteric-coated mycophenolate sodium, tacrolimus, and steroids. Blood samples were collected up to 12 hours after drug administration.

RESULTS

MPA and fMPA pharmacokinetics were similar for patients <60 and >60 years; however, the MPA area under the concentration-time curve from 0 to 12 hours (AUC_0-12) was 1.2-fold lower in the older patients. MPAG pharmacokinetics were more than 1.5-fold higher in patients >60 years, which might be related to deteriorated renal function in older people. Moreover, the mean (MPAG AUC_0-12)/(MPA AUC_0-12) ratio was more than 2-fold higher in patients >60 years. The second maximal MPA concentration was more frequently observed in patients <60 years, although all patients received tacrolimus. The percentage of patients with MPA concentration before the next drug dose (C_trough) and AUC_0-12 within and below target was the same in both groups. All patients >60 years had MPA AUC_0-12 >30 μg·h/mL within 22 to 114 days after transplantation.

CONCLUSIONS

MPA therapeutic monitoring should be recommended in enteric-coated mycophenolate sodium--treated patients >60 years because MPA AUC_0-12 exceeded the recommended value in half of the studied patients.

Establishment of a Liquid Chromatography-Tandem Mass Spectrometry Method for the Determination of Immunosuppressant Levels in the Peripheral Blood Mononuclear Cells of Chinese Renal Transplant Recipients

BACKGROUND

Monitoring immunosuppressant levels, such as mycophenolic acid (MPA), cyclosporin A (CsA), and tacrolimus (TAC), in peripheral blood mononuclear cells (PBMCs) could be useful in organ transplant patients administered individualized therapy. The authors developed a liquid chromatography-tandem mass spectrometry assay technique to simultaneously determine immunosuppressant levels in PBMCs and assess their pharmacokinetics in Chinese renal allograft recipients.

METHODS

PBMCs were isolated from the whole blood of 27 Chinese renal transplant patients using Ficoll-Paque Plus solution, and cell number was determined; acetonitrile treatment for protein precipitation, and gradient elution was performed on an Agilent Eclipse XDB-C18 column (3.5 μm, 2.1 × 100 mm) with mobile phase: water and methanol (containing 2 mM ammonium formate); flow rate: 0.3 mL·min.

RESULTS

The calibration curves of MPA, CsA, and TAC had a linear range (ng·mL): 0.098-39.2 (r = 0.9987), 0.255-102 (r = 0.9969), and 0.028-11.2 (r = 0.9993), respectively. The extraction effects, matrix effects, and mean relative recovery of these immunosuppressants were 70.4%-93.2%, 72.7%-96.5%, and 90.1%-112.4%, respectively. The within-day and between-day coefficients of variation were <15%. The AUC0-12 of MPA in PBMCs correlated well with those in plasma. The level of MPA, CsA, and TAC in PBMCs might be more stable during dosing interval.

CONCLUSIONS

The derived liquid chromatography-tandem mass spectrometry assay is suitable for simultaneously monitoring different immunosuppressants in PBMCs. Pharmacokinetic of MPA, CsA, and TAC displayed considerable interindividual variability. Intracellular monitoring of immunosuppressants may facilitate individualized therapy for renal allograft recipients.

Limited Sampling Strategy for Estimating Mycophenolic Acid Exposure on Day 7 Post-Transplant for Two Mycophenolate Mofetil Formulations Derived From 20 Chinese Renal Transplant Recipients

PURPOSE

To assess the pharmacokinetic properties of mycophenolate mofetil (MMF) dispersible tablets and capsules by the enzyme multiplied immunoassay technique (EMIT) in Chinese kidney transplant recipients in the early post-transplantation phase and to develop the equations to predict mycophenolic acid (MPA) area under the 12-hour concentration-time curve (AUC_0-12h) using a limited sampling strategy (LSS).

METHODS

Forty patients who underwent renal transplantation from brain-dead donors were randomly divided into dispersible tablets (Sai KE Ping; Hangzhou Zhongmei Huadong Pharma) and capsules (Cellcept; Roche Pharma, Why, NSW, Australia) groups, and treated with MMF combined with combination tacrolimus and prednisone as a basic immunosuppressive regimen. Blood samples were collected before treatment (0) and at 0.5,1, 1.5, 2, 4, 6, 8, 10, and 12 hours post-treatment and 7 days after renal transplantation. Plasma MPA concentrations were measured using EMIT. LSS equations were identified using multiple stepwise linear regression analysis.

RESULTS

The peak concentration (C_max) in the MMF dispersible tablets (MMFdt) group (7.0 ± 2.8) mg/L was reduced compared with that in the MMF capsules (MMFc) group (10.8 ± 6.2 mg/L; P = .012); time to peak concentration in the MMFdt group was 3.2 ± 2.3 hours, which was nonsignificantly elevated compared with that of the MMFc group (2.2 ± 1.7 hours). Three-point estimation formulas were generated by multiple linear regression for both groups: MPA-AUC_MMFdt = 3.542 + 3.332C_0.5h + 1.117C_1.5h + 3.946C_4h (adjusted r² = 0.90, P < .001); MPA-AUC_MMFc = 8.149 + 1.442C_2h + 1.056C_4h + 7.133C_6h (adjusted r² = 0.88, P < .001). Both predicted and measured AUCs showed good consistency.

CONCLUSIONS

After treatment with MMF dispersible tables or MMF capsules, the C_max of MPA for the MMFdt group was significantly lower than that of the MMFc group; there was no significant difference in other pharmacokinetic parameters. Three-time point equations can be used as a predictable measure of the AUC_0-12h of MPA.

Estimation of Mycophenolic Acid Area Under the Curve With Limited-Sampling Strategy in Chinese Renal Transplant Recipients Receiving Enteric-Coated Mycophenolate Sodium

BACKGROUND

The enteric-coated mycophenolate sodium (EC-MPS), whose active constituent is mycophenolic acid (MPA), has been widely clinically used for organ transplant recipients. However, its absorption is delayed due to its special designed dosage form, which results in difficulty to monitor the exposure of the MPA in patients receiving the EC-MPS. This study was aimed at developing a relatively practical and precise model with limited sampling strategy to estimate the 12-hour area under the concentration-time curve (AUC0-12 h) of MPA for Chinese renal transplant recipients receiving EC-MPS.

METHODS

A total of 36 Chinese renal transplant recipients receiving the EC-MPS and tacrolimus were recruited in this study. The time point was 2 weeks after the transplantation for all the patients. The MPA concentrations were measured with enzyme-multiplied immunoassay technique for 11 blood specimens collected predose and at 0.5, 1, 1.5, 2, 2.5, 3, 4, 6, 8, and 12 hours after the morning dose of EC-MPS. The measured AUC was calculated with these 11 points of MPA concentrations with the linear trapezoidal rule. Limited sampling strategy was used to develop models for estimated AUC in the model group (n = 18). The bias and precision of different models were evaluated in the validation group (n = 18).

RESULTS

C4 showed the strongest correlation with the measured AUC. The best 3 time point equation was 6.629 + 8.029 × C0 + 0.592 × C3 + 1.786 × C4 (R = 0.910; P < 0.001), whereas the best 4 time point equation was 3.132 + 5.337 × C0 + 0.735 × C3 + 1.783 × C4 + 3.065 × C8 (R = 0.959; P < 0.001). When evaluated in the validation group, the 4 time point model had a much better performance than the 3 time point model: for the 4 time point model: R = 0.873, bias = 0.505 [95% confidence interval (CI), -10.159 to 11.170], precision = 13.370 (95% CI, 5.186-21.555), and 77.8% of estimated AUCs was within 85%-115% of the measured AUCs; for the 3 time point model: R = 0.573, bias = 6.196 (95% CI, -10.627 to 23.018), precision = 21.286 (95% CI, 8.079-34.492), and 50.0% of estimated AUCs was within 85%-115% of the measured AUCs.

CONCLUSIONS

It demanded at least 4 time points to develop a relatively reliable model to estimate the exposure of MPA in renal transplant recipients receiving the EC-MPS. The long time span needed restricted its application, especially for the outpatients, but it could be a useful tool to guide the personalized prescription for the inpatients.

Pharmacokinetics, Pharmacodynamics, and Pharmacogenomics of Immunosuppressants in Allogeneic Hematopoietic Cell Transplantation: Part II

Part I of this article included a pertinent review of allogeneic hematopoietic cell transplantation (alloHCT), the role of postgraft immunosuppression in alloHCT, and the pharmacokinetics, pharmacodynamics, and pharmacogenomics of the calcineurin inhibitors and methotrexate. In this article (Part II), we review the pharmacokinetics, pharmacodynamics, and pharmacogenomics of mycophenolic acid (MPA), sirolimus, and the antithymocyte globulins (ATG). We then discuss target concentration intervention (TCI) of these postgraft immunosuppressants in alloHCT patients, with a focus on current evidence for TCI and on how TCI may improve clinical management in these patients. Currently, TCI using trough concentrations is conducted for sirolimus in alloHCT patients. Several studies demonstrate that MPA plasma exposure is associated with clinical outcomes, with an increasing number of alloHCT patients needing TCI of MPA. Compared with MPA, there are fewer pharmacokinetic/dynamic studies of rabbit ATG and horse ATG in alloHCT patients. Future pharmacokinetic/dynamic research of postgraft immunosuppressants should include '-omics'-based tools: pharmacogenomics may be used to gain an improved understanding of the covariates influencing pharmacokinetics as well as proteomics and metabolomics as novel methods to elucidate pharmacodynamic responses.

Clinical pharmacy service practice in a Chinese tertiary hospital

Clinical pharmacy service is focused on the rationality and safety of medication therapy. Clinical pharmacists play an important role in designing therapeutic regimen, preventing medication errors, reducing the incidence of adverse drug reaction, and saving medical costs. Although clinical pharmacy service in China is in its early stage, its development is rapid. In this manuscript, the working model of clinical pharmacists in a Chinese tertiary hospital is introduced, including ward rounds, consultation, stewardship of antimicrobial therapy, drug adverse reaction monitoring, therapeutic drug monitoring, clinical pharmacokinetics and pharmacogenetics, and training system. With the efforts of clinical pharmacists, there will be a significant increase in the optimization of medication therapy and a notable reduction in preventable adverse drug events as well as health-care cost in China.

Limited sampling strategy for predicting area under the concentration-time curve for mycophenolic Acid in Chinese adults receiving mycophenolate mofetil and tacrolimus early after renal transplantation

BACKGROUND

The objective of the study was to investigate the pharmacokinetics of mycophenolate mofetil (MMF) in Chinese adults early after renal transplantation by an enzyme multiplied immunoassay technique and to establish a limited sampling strategy to predict the area under the concentration-time curve for plasma levels of mycophenolic acid (MPA-AUC).

METHODS

Fifty-eight recipients who underwent renal transplantation with an organ donated after cardiac death used a triple immunosuppressant strategy of MMF, tacrolimus, and prednisone. On the seventh day posttransplantation, plasma samples were collected at 0 hours (pre-dose) and at 0.5, 1, 1.5, 2, 4, 6, 8, 10, and 12 hours postdose (C0h, C0.5h, C1h, C1.5h, C2h, C4h, C6h, C8h, C10h, and C12h, respectively). Enzyme multiplied immunoassay technique was used to measure mycophenolic acid concentration, and model equations were generated by multiple stepwise regression analysis to determine MPA-AUC0-12h.

RESULTS

The 3-point equation obtained by multiple linear regression analysis was MPA-AUC = 7.951 + 4.04C6h + 1.893C2h + 4.542C10h (adjusted r = 0.863); the 4-point equation was MPA-AUC = 4.272 + 4.074C6h + 1.896C2h + 4.680C10h + 0.859C0.5h (adjusted r = 0.918). The % mean prediction error, % mean absolute error, and % root mean squared prediction error for the best-fit formula using C6h, C2h, C10h, and C0.5h were -0.2%, 8.7%, and 14.2%, respectively.

CONCLUSIONS

In Chinese adults receiving MMF and tacrolimus early after renal transplantation, the best equation for predicting MPA-AUC0-12h is 4.272 + 4.074C6h + 1.896C2h + 4.680C10h + 0.859C0.5h.

A Comparison of the Immunochemical Methods, PETINIA and EMIT, With That of HPLC-UV for the Routine Monitoring of Mycophenolic Acid in Heart Transplant Patients

BACKGROUND

The aim of this study was to evaluate particle enhanced turbidimetric inhibition immunoassay (PETINIA) recently developed for mycophenolic acid (MPA) determination in plasma and to compare it with a reference high-performance liquid chromatography (HPLC) method, using samples from heart transplant recipients. The results are presented in the context of PETINIA being compared with enzyme multiplied immunoassay technique (EMIT).

METHODS

PETINIA evaluation was performed using 194 routine trough plasma samples at steady state. EMIT was evaluated using 677 samples from 61 steady-state 12-hour profiles obtained from 35 heart transplant patients. Evaluation was undertaken on a Dimension EXL 200 analyzer (PETINIA) and on a Viva-E analyzer (EMIT).

RESULTS

The mean MPA concentration measured by PETINIA was significantly higher than that measured by high-performance liquid chromatography combined with UV detector (2.36 ± 1.30 mcg/mL versus 1.82 ± 1.23 mcg/mL, respectively, P < 0.0001). Bland-Altman analysis revealed a mean bias of 0.54 mcg/mL [95% confidence interval (CI), 0.49-0.59] comprising 33.48% (95% CI, 30.34-36.61). Passing-Bablok regression was: y = 1.100x + 0.38 (95% CI for slope: 1.044-1.154 and for intercept: 0.30-0.47). Regardless of a significant observed correlation (r = 0.9230, P < 0.0001), the statistical analyses showed a significant difference between PETINIA and the reference chromatographic method. The mean MPA concentration measured by EMIT was significantly higher than that measured by HPLC (7.48 ± 8.34 mcg/mL versus 5.57 ± 6.61 mcg/mL, respectively, P < 0.0001) with a mean bias of 1.91 mcg/mL (95% CI, 1.75-2.07) comprising 35.91% (95% CI, 34.37-37.45). The significant difference between EMIT and HPLC was confirmed by Passing-Bablok regression: y = 1.300x + 0.24 (95% CI for slope: 1.279-1.324 and for intercept: 0.18-0.29). The analysis of the determinations, grouped by sampling time, revealed positive bias between EMIT and HPLC ranging from 24.54% to 42.77% and inversely proportional to MPA concentrations with r = 0.9122 (P < 0.001).

CONCLUSIONS

The new immunochemical PETINIA method was associated with significantly higher MPA concentrations in routine therapeutic drug monitoring samples from heart transplant patients. The magnitude of the MPA overestimation was similar to that observed by use of the EMIT method.

Monitoring of mycophenolate mofetil metabolites in children with nephrotic syndrome and the proposed novel target values of pharmacokinetic parameters

The aim of the study was to estimate target values of mycophenolate mofetil (MMF) pharmacokinetic parameters in children with proteinuric glomerulopathies by calculating the pharmacokinetic parameters of MMF metabolites (mycophenolic acid [MPA], free MPA [fMPA] and MPA glucuronide [MPAG]) and assessing their relation to proteinuria recurrence. One hundred and sixty-eight blood samples were collected from children, aged 3-18 years, diagnosed with nephrotic syndrome or lupus nephritis. MMF metabolites concentrations were examined before drug administration (Ctrough) and up to 12h afterward employing high-performance liquid chromatography. Dose-normalized MPA Ctrough and area under the concentration-time curve from 0 to 12h (AUC12) were within 0.29-6.47 μg/mL/600 mg/m(2) and 9.97-105.52 μg h/mL/600 mg/m(2), respectively. MPA Ctrough was twofold lower (p=0.024) in children with proteinuria recurrence. MPA, fMPA and MPAG concentrations correlated positively to respective AUC12. It may be suggested MMF metabolites monitoring in children with proteinuric glomerulopathies is justified by MPA Ctrough<2 μg/mL in patients at risk of the proteinuria recurrence. Such a recurrence is most probably caused by not sufficient MPA concentration during proteinuric glomerulopathies treatment. MPA Ctrough>3 μg/mL may be considered as an efficient one to avoid proteinuria recurrence. Finally, MPA target AUC12 should exceed 60 μg h/mL to ensure the safe and effective treatment in children with nephrotic syndrome, however, the upper limit is still to be established.

Correlation between mycophenolic acid blood level and renal dysfunction in stable liver transplant recipients receiving mycophenolate monotherapy

PURPOSE

Mycophenolate mofetil (MMF) is frequently used after liver transplantation (OLT). Mycophenolic acid (MPA) metabolites are eliminated primarily via the kidneys. If renal function declines, clearance is significantly impaired. The aim of this study was to reveal the renal function-dependent changes of MPA level in stable adult OLT recipients receiving MMF monotherapy.

METHODS

Sixty-five OLT recipients were selected from our OLT database of >3500 cases. All had undergone MMF monotherapy with a daily MMF dose of 1000 mg or 1500 mg for more than 2 years, primarily because they could not tolerate calcineurin inhibitors. Their clinical profiles, including MPA therapeutic drug monitoring (TDM) and renal function, were analyzed as a cross-sectional study.

RESULTS

For the group treated with 1000 mg MMF (n = 40), the 12-hour MPA trough level was 1.20 ± 0.35 μg/mL with serum creatinine (Cr) level ≤1.4 mg/dL in 13 patients; it was 2.78 ± 1.19 μg/mL with Cr >1.4 mg/dL in 16 patients not undergoing hemodialysis and 3.83 ± 0.87 μg/mL in 11 patients undergoing hemodialysis (P < .001). For the group treated with 1500 mg MMF (n = 25), the MPA trough level was 2.23 ± 0.99 μg/mL with Cr ≤1.4 mg/dL in 6 patients; it was 2.81 ± 0.99 μg/mL with Cr >1.4 mg/dL in 18 patients not undergoing hemodialysis and 3.5 μg/mL in 1 patient undergoing hemodialysis (P = .21).

CONCLUSIONS

Considering the potential therapeutic range of MPA, the suggested MMF dosage for Korean adult OLT recipients requiring hemodialysis may be set around 1000 mg per day. We suggest adjusting the MMF dosage on an individualized basis according to the results of MPA TDM, particularly for patients with markedly impaired renal function.

Pharmacokinetics of mycophenolate sodium co-administered with tacrolimus in the first year after renal transplantation

We assessed the relations between MPA, free MPA (fMPA) and MPA glucuronide (MPAG) pharmacokinetics and the clinical condition of renal transplant recipients treated with EC-MPS and tacrolimus (Tac) in the first post-transplant year. In 18 adult patients blood samples were collected up to 12 h after EC-MPS oral administration. EC-MPS metabolites' plasma concentrations were determined using validated HPLC methods. All patients reached MPA area under the time-concentration curve (AUC0-12) above 30 µg h/mL. Most of the MPA, fMPA and all MPAG concentrations correlated significantly with respective AUC0-12 values. Some fMPA and all MPAG pharmacokinetic parameters correlated negatively with creatinine clearance and positively with creatinine concentration, whereas no such correlation was observed for MPA. Lower hemoglobin concentrations were observed in patients with higher MPA or fMPA C 0. The significant correlations between MPA C 3 as well as MPA C 4 and MPA AUC0-4 and MPA AUC0-12 may be of importance in further studies including larger number of patients in regard to establishing LSS. In patients treated with EC-MPS and Tac, monitoring MPA C 0 may be important, as too high MPA C 0 may contribute to anemia onset. In EC-MPS treated patients, MPAG concentration is related to renal function as MPAG pharmacokinetics were higher in patients with renal impairment.

Clinical mycophenolic acid monitoring in liver transplant recipients

In liver transplantation, the efficacy of mycophenolate mofetil (MMF) has been confirmed in clinical trials and studies. However, therapeutic drug monitoring for mycophenolic acid (MPA) has not been fully accepted in liver transplantation as no long-term prospective study of concentration controlled vs fixed-dose prescribing of MMF has been done. This review addressed MPA measurement, pharmacokinetic variability and reasons of this variation, exposure related to acute rejection and MMF-associated side effects in liver transplant recipients. Limited sampling strategies to predict MPA area under the concentration-time curve have also been described, and the value of clinical use needs to be investigated in future. The published data suggested that a fixed-dosage MMF regimen might not be suitable and monitoring of MPA exposure seems helpful in various clinical settings of liver transplantation.

Pharmacology and toxicology of mycophenolate in organ transplant recipients: an update

This review aims to provide an update of the literature on the pharmacology and toxicology of mycophenolate in solid organ transplant recipients. Mycophenolate is now the antimetabolite of choice in immunosuppressant regimens in transplant recipients. The active drug moiety mycophenolic acid (MPA) is available as an ester pro-drug and an enteric-coated sodium salt. MPA is a competitive, selective and reversible inhibitor of inosine-5'-monophosphate dehydrogenase (IMPDH), an important rate-limiting enzyme in purine synthesis. MPA suppresses T and B lymphocyte proliferation; it also decreases expression of glycoproteins and adhesion molecules responsible for recruiting monocytes and lymphocytes to sites of inflammation and graft rejection; and may destroy activated lymphocytes by induction of a necrotic signal. Improved long-term allograft survival has been demonstrated for MPA and may be due to inhibition of monocyte chemoattractant protein 1 or fibroblast proliferation. Recent research also suggested a differential effect of mycophenolate on the regulatory T cell/helper T cell balance which could potentially encourage immune tolerance. Lower exposure to calcineurin inhibitors (renal sparing) appears to be possible with concomitant use of MPA in renal transplant recipients without undue risk of rejection. MPA displays large between- and within-subject pharmacokinetic variability. At least three studies have now reported that MPA exhibits nonlinear pharmacokinetics, with bioavailability decreasing significantly with increasing doses, perhaps due to saturable absorption processes or saturable enterohepatic recirculation. The role of therapeutic drug monitoring (TDM) is still controversial and the ability of routine MPA TDM to improve long-term graft survival and patient outcomes is largely unknown. MPA monitoring may be more important in high-immunological recipients, those on calcineurin-inhibitor-sparing regimens and in whom unexpected rejection or infections have occurred. The majority of pharmacodynamic data on MPA has been obtained in patients receiving MMF therapy in the first year after kidney transplantation. Low MPA area under the concentration time from 0 to 12 h post-dose (AUC0-12) is associated with increased incidence of biopsy-proven acute rejection although AUC0-12 optimal cut-off values vary across study populations. IMPDH monitoring to identify individuals at increased risk of rejection shows some promise but is still in the experimental stage. A relationship between MPA exposure and adverse events was identified in some but not all studies. Genetic variants within genes involved in MPA metabolism (UGT1A9, UGT1A8, UGT2B7), cellular transportation (SLCOB1, SLCO1B3, ABCC2) and targets (IMPDH) have been reported to effect MPA pharmacokinetics and/or response in some studies; however, larger studies across different ethnic groups that take into account genetic linkage and drug interactions that can alter a patient's phenotype are needed before any clinical recommendations based on patient genotype can be formulated. There is little data on the pharmacology and toxicology of MPA in older and paediatric transplant recipients.

Pharmacokinetics of free mycophenolic acid and limited sampling strategy for the estimation of area under the curve in liver transplant patients

Mycophenolate Mofetil (MMF) is widely used in preventing acute rejection in liver transplantation. Only free MPA (fMPA) can exert the pharmacological effect. In this study, we aimed to develop the new model which could be best fit to predict the fMPA area under the plasma concentration-time curve (AUC) by limited sampling strategy (LSS) in Chinese liver transplant patients. Fifty patients received MMF with the combination of tacrolimus. Free MPA concentrations were determined around day 7. Optimal subset regression analysis was used to establish the models for estimated fMPA AUC(0-12h). Three excellent better models were validated by Bootstrap analysis. Twenty-four models including four blood time point samplings were established. For the selected four models, 100% were successful and were not significantly different from the original dataset by Bootstrap analysis. The best model for prediction of fMPA AUC(0-12h) was by using C(1h), C(2h), C(4h) and C(6h). This model showed the minimal mean prediction error and the minimal mean absolute prediction error. In conclusion, the models for estimation of the fMPA AUC(0-12h) were established in liver transplant recipients and the best model for prediction of fMPA AUC was: estimated fMPA AUC=34.2+1.12C(1h)+1.29C(2h)+2.28C(4h)+3.95C(6h).