Pharmacokinetics of mycophenolic acid and determination of area under the curve by abbreviated sampling strategy in Chinese liver transplant recipients

Decrease in Mycophenolic Acid Plasma Level by Sacubitril/Valsartan in a Lupus Nephritis Patient: A Case Report

Introduction

Mycophenolate mofetil (MMF), an inactive prodrug of mycophenolic acid (MPA), is an immunosuppressive drug used widely in the treatment of lupus nephritis. In this case report, the area under the blood concentration time curve (AUC) of MPA was significantly decreased by the concomitant use of sacubitril/valsartan.

Case Presentation

The patient was a man in his 40s with a diagnosis of lupus nephritis class IVa/c+V. MMF dose was 1.5 g/day at admission, and AUC of MPA on day 14 was 25.1 μg⋅h/mL. Owing to poor blood pressure control, sacubitril/valsartan was initiated at 97/103 mg/day on day 29. On day 37, AUC of MPA was significantly decreased to 8.7 μg⋅h/mL, suggesting drug interaction with the newly initiated sacubitril/valsartan. Sacubitril/valsartan was decreased to 49/51 mg/day, and AUC of MPA on day 67 was 37.6 μg⋅h/mL, achieving the target range. The final MMF dose was set at 1.75 g/day. A possible mechanism of drug interaction between sacubitril/valsartan and MPA involves an organic anion transporting polypeptide (OATP). The inhibition of OATPs by sacubitril may have interrupted the enterohepatic circulation of MPA, resulting in a lower plasma concentration.

Conclusion

Since lupus nephritis is often associated with hypertension, the drug interaction observed in this report may also occur in other cases. However, it is impossible to conclude that the decrease in plasma MPA levels was due to the concomitant use of sacubitril/valsartan, and more cases and basic findings are needed.

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.

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.

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.

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.

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).

The occurrence of diarrhea not related to the pharmacokinetics of MPA and its metabolites in liver transplant patients

PURPOSE

Mycophenolate mofetil (MMF) is a pro-drug that is hydrolyzed to release mycophenolic acid (MPA). Subsequently MPA is extensively metabolized to phenyl mycophenolic acid glucuronide (MPAG) and MPA acyl glucuronide (AcMPAG). It was presumed that the closest association is between plasma AcMPAG concentrations and the incidence of diarrhea. This study aimed to investigate the correlation between pharmacokinetics of MPA, MPAG, and AcMPAG and diarrhea in liver transplant recipients on MMF with tacrolimus.

METHODS

Sixty-seven patients receiving liver transplantation were included. The pharmacokinetics of MPA and its metabolites were monitored repeatedly in the early stage (within 2 weeks) and in the late stage after transplant. The plasma concentrations of MPA, MPAG, and AcMPAG were determined by the HPLC method.

RESULTS

Twenty-two patients (32.8%) suffered from episodes of diarrhea. Compared with the data from the early stage, AUC(0-12h) of MPA, MPAG, and AcMPAG increased significantly in both groups in the later stage. AUC(0-12h) of MPA, MPAG, and AcMPAG were not different significantly between the group with diarrhea and the group without diarrhea, either in the early stage or in the late stage (P > 0.05).

CONCLUSION

These results suggest that systemic exposures to MPA and its metabolites are not associated with the incidence of diarrhea in liver transplant recipients.

Limited sampling strategies for mycophenolic acid in solid organ transplantation: a systematic review

BACKGROUND

Mycophenolic acid (MPA) is the active metabolite of mycophenolate mofetil, a widely used immunosuppressant. Numerous studies have developed limited sampling strategies (LSSs) to predict MPA AUC in solid organ transplant recipients.

OBJECTIVES

To systematically review and assess quality of literature pertaining to MPA LSSs, evaluate clinical implications and provide suggestions for future research.

METHODS

Literature searches of MEDLINE (1966 - May 2009) and EMBASE (1980 - May 2009) for English articles in solid organ transplantation, along with manual review of article references were conducted. Included articles were categorized according to criteria adapted from levels of evidence of the US Preventative Services Task Force.

RESULTS

Of a total of 29 studies identified, 20 were in kidney, 4 in heart, 4 in liver and 1 in lung transplantation and 7 were in pediatrics. A total of 14 studies were deemed to be Level I evidence studies, 3 were Level II-1, 1 was Level II-2 and 11 were Level III.

CONCLUSIONS

Although various LSSs that are well correlated to MPA AUC while being relatively unbiased and precise to predict MPA AUC have been developed, further research is needed to determine validity of these LSSs in a variety of patient populations and to determine if these LSSs improve patient outcomes.

Comparison of pharmacokinetics of mycophenolic acid and its metabolites between living donor liver transplant recipients and deceased donor liver transplant recipients

Living-donor liver transplantation (LDLT) has been considered an alternative method for treatment of patients with end-stage liver disease. However, the characteristics of pharmacokinetics of mycophenolic acid (MPA) in patients who underwent LDLT were not clear. This study was designed to compare the pharmacokinetics of MPA and its metabolites between LDLT patients and deceased donor liver transplant (DDLT) patients after oral administration of mycophenolate mofetil (MMF). Thirteen patients who underwent LDLT and 14 patients who underwent DDLT were enrolled prospectively. All patients received oral MMF administration (1.0 g, twice daily) in combination with tacrolimus (TAC). The plasma concentrations of MPA, free MPA, glucuronide (MPAG), and acyl glucuronide (AcMPAG) was determined by high-performance liquid chromatography method. There was a wide variation in various pharmacokinetic parameters of MPA and its metabolites in patients who underwent LDLT and DDLT after oral MMF administration. Although mean MPA area under the plasma concentration time curve for 0-12 hours (AUC(0-12h)) of MPA and MPAG in DDLT patients were higher than those in LDLT patients, there was no significant difference between the two groups. MPA concentration at 6 hours (C(6h)), C(10h), C(12h), and MPA AUC(6-12h) were significantly higher in DDLT group than those in LDLT group (P < 0.05). Inversely, higher free MPA AUC(0-12h) and significant free MPA fraction (P < 0.05) in LDLT patients were observed in DDLT patients when compared with DDLT group. AcMPAG concentrations at 4, 8, and 10 hours and AcMPAG AUC(0-12h) were significantly higher in the DDLT group (P < 0.05). In conclusion, after a fixed oral dose of MMF, DDLT patients had higher enterohepatic recycling contributing to total MPA exposure compared with LDLT patients. The function of glucuronide conjugation in LDLT patients was decreased compared with that in DDLT patients. Higher free MPA AUC(0-12h) and a significantly higher fraction of free MPA in LDLT patients suggested that a lower oral dose of MMF may be administered for patients who underwent LDLT.

Models for the prediction of mycophenolic acid area under the curve using a limited-sampling strategy and an enzyme multiplied immunoassay technique in Chinese patients undergoing liver transplantation

BACKGROUND

An enzyme multiplied immunoassay technique (EMIT) provides convenient and accurate measurements of mycophenolic acid (MPA) concentrations for determination of immunosuppression during treatment with mycophenolate mofetil (MMF). No abbreviated model for estimating the full 12-hour MPA AUC using an EMIT assay in liver transplant recipients has been described previously.

OBJECTIVE

This study was conducted to determine the best model for predicting the MPA AUC using the EMIT method and a limited-sampling strategy in Chinese patients undergoing liver transplantation.

METHODS

The study enrolled consecutive liver transplant patients who were receiving MMF 1 g BID along with tacrolimus. A complete MPA pharmacokinetic profile was obtained for each patient on a single day, 7 to 14 days after transplantation. The EMIT method was used to determine MPA concentrations before dosing and at 0.5, 1, 1.5, 2, 4, 6, 8, 10, and 12 hours after dosing on the sampling day. Multiple linear regression analysis was used to evaluate potential models for estimating the full 12-hour MPA AUC. The accuracy and robustness of the models were evaluated using bootstrap analysis. Prediction error and prediction bias were calculated. Agreement between the estimated MPA AUC(0-12) and the full 12-hour MPA AUC was investigated using Bland-Altman analysis.

RESULTS

The study enrolled 48 Chinese liver transplant recipients (45 male, 3 female) with a mean (SD) age of 50 (12) years, mean weight of 64 (12) kg, and mean height of 169 (6) cm. Twenty-four models that included blood sampling at 1 through 4 time points were developed (r(2) = 0.015-0.950). Four models with the highest r(2) values were selected; the lack of significant differences from the original dataset on bootstrap analysis indicated acceptable accuracy and robustness. The best model for predicting the MPA AUC(0-12) employed concentrations at 1, 2, 4, and 8 hours; 40 of 48 (83.3%) MPA AUC(0-12) values estimated using this model were within 15% of the full 12-hour MPA AUC. This model had a minimal mean prediction error (mean [SD], 0.27% [1.79%]) and mean absolute prediction error (8.83% [1.24%]). On Bland-Altman analysis, this model also had the best agreement between the estimated MAP AUC(0-12) and the full 12-hour MPA AUC, with a mean error of 9.02 mg . h/L.

CONCLUSIONS

In this small group of Chinese liver transplant patients receiving MMF and concomitant tacrolimus, models for estimating the MPA AUC(0-12) were developed using the EMIT method and a limited-sampling strategy. The best model for prediction of the full 12-hour MPA AUC was 4.46 + 0.81 . C1 + 1.78 . C(2)+2.51.C(4)+4.94.C8.

A limited sampling strategy for estimating mycophenolic acid area under the curve in adult heart transplant patients treated with concomitant cyclosporine

OBJECTIVE

Heart transplantation studies have shown a relationship between the mycophenolic acid area under the curve (AUC) 0-12 h (MPA AUC(0-12h)) values and risk of acute rejection episodes and fewer side-effects in patient receiving cyclosporine during the first year post-transplant. However, measurement of full AUC is costly and time consuming and in this case it is an impractical approach to drug monitoring. Therefore, the authors describe a limited sampling strategy to estimate the MPA AUC(0-12h) value in adult heart transplant recipients.

METHODS

Ninety MPA pharmacokinetic (PK) profiles were studied. The samples were collected immediately before and 0.5, 1, 1.5, 2, 2.5, 3, 4, 6, 9, 12 h after the morning dose of mycophenolate mofetil (MMF) following an overnight fast. PK profiles were determined at 6-8 weeks, 6, 12 months and more than 1 year after transplantation. Using stepwise multiple linear regression analysis a sampling strategy from 60 of PK profiles was obtained and next the bias and precision of the model were evaluated in another 30 PK profiles.

RESULTS

The three-point model using C(0.5h), C(1h), C(2h) was found to be superior to all other models tested (r(2) = 0.841). The regression equation for AUC estimation which gave the best fit to this model is: 9.69 + 0.63C(0.5) + 0.61C(1) + 2.20C(2). Using that model 63 of the 90 (70%) full AUC values were estimated within 15% of their actual value. For the best-fit model, the mean prediction error was 3.2%, with 95% confidence intervals for prediction error to range from -42.2% to 40.3%. All other models which use one, two or three time-points over the first 2 h are poorer predictors of the full AUC than the model above.

CONCLUSION

The proposed three time-point equation to estimate AUC will be helpful in optimizing immunosuppressive therapy in heart transplantation.

Pharmacokinetic study of mycophenolate mofetil in patients with systemic lupus erythematosus and design of Bayesian estimator using limited sampling strategies

BACKGROUND

Monitoring of the area under the plasma concentration-time curve (AUC) of mycophenolic acid (MPA) has been developed for individual dose adjustment of mycophenolate mofetil (MMF) in renal allograft recipients. MMF is currently used as an off-label drug in the treatment of systemic lupus erythematosus (SLE), but factors of its exposition may be different in these patients and need to be determined for therapeutic drug monitoring (TDM) purposes.

OBJECTIVE

The aim of the study was to develop a maximum a posteriori probability (MAP) Bayesian estimator of MPA exposition in patients with SLE, with the objective of TDM based on a limited sample strategy.

METHODS

Twenty adult patients with SLE given a stable 1 g/day, 2 g/day or 3 g/day dose of MMF orally for at least 10 weeks were included in the study. MPA was measured by high-performance liquid chromatography (HPLC) coupled to a photodiode array detector (11 plasma measurements over 12 hours post-dose per patient). Free MPA concentrations were measured by HPLC with fluorescence detection. Two different one-compartment models with first-order elimination were tested to fit the data: one convoluted with a double gamma distribution to describe secondary concentrations peaks, and one convoluted with a triple gamma distribution to model a third, later peak.

RESULTS

A large interindividual variability in MPA concentration-time profiles was observed. The mean maximum plasma concentration, trough plasma concentration, time to reach the maximum plasma concentration and AUC from 0 to 12 hours (AUC(12)) were 13.6 +/- 8.4 microg/mL, 1.4 +/- 1.2 microg/mL, 1.1 +/- 1.2 hours and 32.2 +/- 17.1microg . h/mL, respectively. The mean free fraction of MPA was 1.7%. The one-compartment model with first-order elimination convoluted with a triple gamma distribution best fitted the data. Accurate Bayesian estimates of the AUC(12) were obtained using three blood samples collected at 40 minutes, 2 hours and 3 hours, with a coefficient of correlation (R) = 0.95 between the observed and predicted AUC(12) and with a difference of <20% in 16 of the 20 patients.

CONCLUSION

A specific pharmacokinetic model was built to accurately fit MPA blood concentration-time profiles after MMF oral dosing in SLE patients, which allowed development of an accurate Bayesian estimator of MPA exposure that should allow MMF monitoring based on the AUC(12) in these patients. The predictive value of targeting one specific or different AUC values on patients' outcome using this estimator in SLE will need to be evaluated.

Monitoring mycophenolic acid pharmacokinetic parameters in liver transplant recipients: prediction of occurrence of leukopenia

Mycophenolate mofetil (MMF) is a very powerful immunosuppressive drug used in preventing acute rejection in liver transplantation. However, MMF has some serious side effects, including hematologic and gastrointestinal disorders. This study was designed to investigate the relationship between the clinical events and the pharmacokinetics of mycophenolic acid (MPA) in Chinese liver transplant recipients. Sixty-three adult liver transplant recipients receiving 1.0 g of MMF twice daily in combination with tacrolimus were prospectively included. The MPA pharmacokinetic profiles (blood sampling time points: before the dose and 0.5, 1, 1.5, 2, 4, 6, 8, 10, and 12 hours after the dose) were monitored after transplantation. Every clinical event, including acute and MMF-related side effects, was monitored in all patients within 3 months. Two patients (3.2%) had an episode of acute rejection. Forty-two patients (66.7%) had 52 episodes of MMF-related side effects, including leukopenia, diarrhea, and infection. The 0-hour concentration (C(0h)), maximum (peak) concentration (C(max)), and area under the curve from 0 to 12 hours (AUC(0-12h)) in patients with side effects were significantly higher than those in patients without side effects (P < 0.05). The thresholds of side effects from receiver operating characteristic analysis were 2 mg/L (sensitivity, 52.4%; specificity, 90.5%) for C(0h), 10 mg/L (sensitivity, 45.2%; specificity, 85.7%) for C(max), and 40 mg h/L (sensitivity, 71.4%; specificity, 61.9%) for AUC(0-12h) (P < 0.05). Leukopenia was discriminated effectively in C(0h) and in C(max) (P < 0.05). These results demonstrate the close relationship between leukopenia and MPA pharmacokinetic parameters in the early period after liver transplantation. C(0h) and AUC(0-12h) of MPA could predict the subsequent occurrence of leukopenia. These values may be used in routine monitoring for MMF therapy.

Validation of limited sampling strategy for the estimation of mycophenolic acid exposure in Chinese adult liver transplant recipients

Mycophenolate mofetil (MMF) is indicated as immunosuppressive therapy in liver transplantation. The abbreviated models for the estimation of mycophenolic acid (MPA) area under the concentration-time curve (AUC) have been established by limited sampling strategies (LSSs) in adult liver transplant recipients. In the current study, the performance of the abbreviated models to predict MPA exposure was validated in an independent group of patients. A total of 30 MPA pharmacokinetic profiles from 30 liver transplant recipients receiving MMF in combination with tacrolimus were used to compare 8 models' performance with a full 10 time-point MPA-AUC. Linear regression analysis and Bland-Altman analysis were used to compare the estimated MPA-AUC0-12h from each model against the measured MPA-AUC0-12h. A wide range of agreement was shown when estimated MPA-AUC0-12h was compared with measured MPA-AUC0-12h, and the range of coefficient of determination (r2) was from 0.479 to 0.936. The model based on MPA pharmacokinetic parameters C1h, C2h, C6h, and C8h had the best ability to predict measured MPA-AUC0-12h, with the best coefficient of determination (r2=0.936), the excellent prediction bias (2.18%), the best prediction precision (5.11%), and the best prediction variation (2SD=+/-7.88 mg.h/L). However, the model based on MPA pharmacokinetic sampling time points C1h, C2h, and C4h was more suitable when concerned with clinical convenience, which had shorter sampling interval, an excellent coefficient of determination (r2=0.795), an excellent prediction bias (3.48%), an acceptable prediction precision (14.37%), and a good prediction variation (2SD=+/-13.23 mg.h/L). Measured MPA-AUC0-12h could be best predicted by using MPA pharmacokinetic parameters C1h, C2h, C6h, and C8h. The model based on MPA pharmacokinetic parameters C1h, C2h, and C4h was more feasible in clinical application.

Therapeutic drug monitoring of mycophenolic acid: does it improve patient outcome?

Treatment with the immunosuppressive agent mycophenolate mofetil (MMF) decreases the risk of rejection after renal transplantation and improves graft survival compared with azathioprine. The exposure to the active metabolite mycophenolic acid (MPA) is correlated to the risk of developing acute rejection. The interpatient variability in exposure of MPA is wide relative to the proposed therapeutic window of the MPA AUC(0 12) (30 - 60 mg.h/l). The pharmacokinetics of MPA are influenced by patient characteristics such as gender, time after transplantation, serum albumin concentration, renal function, comedication and pharmacogenetic factors. Therapeutic drug monitoring is likely to reduce inter-patient variability. Limited sampling strategies are used to predict the full AUC(0 12). Three prospective randomised studies compared concentration controlled MMF therapy to a fixed-dose regimen. Preliminary outcomes of these studies showed conflicting results and longer follow up is needed to further clarify the role of therapeutic drug monitoring in increasing the therapeutic potential of MMF.