Simultaneous determination of everolimus and cyclosporine concentrations by HPLC with ultraviolet detection

Development of a metal-organic framework-based nanosensor for determination of cyclosporine in plasma samples

According to the narrow therapeutic range and multiple adverse effects of cyclosporine and the need for its therapeutic drug monitoring (TDM), in this study, an efficient zeolitic imidazolate framework-8 metal-organic framework (ZIF-8 MOF) based nanoprobe was designed for simple, rapid and high sensitive its quantification in plasma samples. After the successful synthesis of the ZIF-8 MOF, under the optimum condition, the fluorescence emission of ZIF-8 MOF, measured at an excitation wavelength of 370 nm and an emission wavelength of 417 nm, was enhanced with increasing cyclosporine concentration, due to the specific interactions between cyclosporine and the nanoprobe, including hydrogen bonding and hydrophobic effects. The nanoprobe showed a linear correlation between the analytical response and cyclosporine concentration in the concentration range of 0.01-1.0 µg mL- 1, with a detection limit of 0.003 µg mL- 1. Acceptable precision was achieved, evidenced by intra-day and inter-day relative standard deviations of 0.4% and 0.5%, respectively. Recovery between 97.1% and 102.1% in plasma samples indicated the method's reliability in practical applications.

Improved LC-MS/MS method for the simultaneous quantification of tacrolimus and cyclosporine A in human blood and application to therapeutic drug monitoring

In order to facilitate therapeutic drug monitoring of tacrolimus and cyclosporine A in clinical practice, a simple, rapid, robust, sensitive and specific LC-MS/MS assay was developed and validated for the simultaneous determination of tacrolimus and cyclosporine A in human whole blood. Erythrocytes were destroyed using internal standard solution with 10% (w/v) zinc sulfate in water. The analytes were extracted from 100 μl of whole blood by protein precipitation with acetonitrile. Chromatographic separation was conducted on a Kinetex PFP column (60°C) by a gradient elution with a flow rate of 0.450 ml/min in 2.5 min. Quantitative analysis was performed using electrospray ionization and multiple reaction monitoring in positive ionization mode. The method was fully validated as per current guidelines on bioanalytical methodologies of the US Food and Drug Administration and European Medicines Agency. The method developed was applied successfully in analyzing clinical samples from patients administered tacrolimus or cyclosporine A. The sample treatment procedure was rationalized and improved to fulfill the complete target extraction. The chromatography conditions were optimized to achieve rapid and accurate quantification of both analytes. This method may be beneficial as a constructive input for the therapeutic drug monitoring of tacrolimus and cyclosporine A in obtaining individualized therapy.

[Rapid and simultaneous determination of two immunosuppressants in whole blood by high performance liquid chromatography]

Cyclosporine A and sirolimus are immunosuppressants that are widely used in many organ transplantation procedures. They exhibit some complementary mechanisms of action and interact synergistically when used together. However， they are critical-dose drugs and have a narrow therapeutic index. They provide the desired therapeutic effect with acceptable tolerability only within a specific range of blood concentrations. Therefore， the rapid and simultaneous detection of the concentrations of cyclosporine A and sirolimus in whole blood could provide valuable information on planning medicine administration after organ transplantations. In this study， firstly， the chromatographic behaviors of cyclosporine A and sirolimus on a biological liquid chromatography （BioLC） column and traditional liquid chromatography （TraLC） columns were investigated systematically under the same chromatographic conditions. The results suggested that the peak height and peak width of cyclosporine A and sirolimus on the BioLC column， ZORBAX 300SB C8 （250 mm×4.6 mm， 5.0 μm）， were the highest and narrowest， respectively. The number of theoretical plates of cyclosporine A and sirolimus on the ZORBAX 300SB C8 column increased significantly when the volume ratio of acetonitrile in the mobile phases was greater than 70%. Their retention time on the BioLC and TraLC columns was negligibly affected by the use of formic acid and trifluoroacetic acid as the mobile phases. In the range of the experimental column temperature， the number of theoretical plates of cyclosporine A and sirolimus on the ZORBAX 300SB C8 column was significantly higher than that on the two TraLC columns. Furthermore， the relationship between the retention factor and column temperature of cyclosporine A on the ZORBAX 300SB C8 column was different from that on the two TraLC columns. Subsequently， a high performance liquid chromatography method based on the ZORBAX 300SB C8 column was established for the rapid separation and determination of cyclosporin A and sirolimus in whole blood. A sample of whole blood with a volume of 50 μL was prepared by protein precipitation with 1 mol/L sodium hydroxide and then extracted into 500 μL of ether-methanol （95∶5， v/v）. After centrifugation at 14000 r/min for 10 min， the organic layer was removed and evaporated under a stream of nitrogen at 50 ℃. The residue was then reconstituted in 200 μL of methanol for use. Cyclosporin A and sirolimus were separated through isocratic elution on the ZORBAX 300SB C8 column. The column temperature was set at 60 ℃. The mobile phase was acetonitrile-water （70∶30， v/v） and the flow rate was 1.0 mL/min. The detection wavelengths were 205 nm for cyclosporine A and 278 nm for sirolimus. The injection volume was 20 μL. The external standard method was used to quantify cyclosporine A and sirolimus. Under the optimized conditions， cyclosporine A and sirolimus were well-separated within 6 min with a resolution of 3.7 at 205 nm. In addition， the endogenous substances in whole blood negligibly interfered in the detection of sirolimus， while two endogenous substances slightly affected the detection of cyclosporine A. Cyclosporine A and sirolimus both showed good linear relationships in their respective concentration （r>0.997）. The limits of detection （LODs） of cyclosporine A and sirolimus were respectively calculated to be 10 ng/mL and 1 ng/mL based on a signal-to-noise ratio of 3， and the limits of quantification （LOQs） were 30 ng/mL and 2 ng/mL based on a signal-to-noise ratio of 10. In the whole blood samples， the recoveries of cyclosporine A and sirolimus at three spiked levels were in the ranges of 83.5%-89.7% and 95.8%-97.8% with relative standard deviations （RSDs） of 3.2%-9.0% and 3.4%-6.7% （n=5）， respectively. The established method is simple in operation， can be performed with a simple mobile phase， has a short analysis time， and provides a wide linear range and high sensitivity； hence， it can be applied to the determination of cyclosporine A and sirolimus in whole blood.

Overview of therapeutic drug monitoring of immunosuppressive drugs: Analytical and clinical practices

Immunosuppressant drugs (ISDs) play a key role in short-term patient survival together with very low acute allograft rejection rates in transplant recipients. Due to the narrow therapeutic index and large inter-patient pharmacokinetic variability of ISDs, therapeutic drug monitoring (TDM) is needed to dose adjustment for each patient (personalized medicine approach) to avoid treatment failure or side effects of the therapy. To achieve this, TDM needs to be done effectively. However, it would not be possible without the proper clinical practice and analytical tools. The purpose of this review is to provide a guide to establish reliable TDM, followed by a critical overview of the current analytical methods and clinical practices for the TDM of ISDs, and to discuss some of the main practical aspects of the TDM.

Quantitative Analysis of Immunosuppressive Drugs Using Tungsten Disulfide Nanosheet-Assisted Laser Desorption Ionization Mass Spectrometry

For organ transplantation patients, the therapeutic drug monitoring (TDM) of immunosuppressive drugs is essential to prevent the toxicity or rejection of the organ. Currently, TDM is done by immunoassays or liquid chromatography-tandem mass spectrometry (LC-MS/MS) methods; however, these methods lack specificity or are expensive, require high levels of skill, and offer limited sample throughput. Although matrix-assisted (MA) laser desorption ionization (LDI) mass spectrometry (MS) can provide enhanced throughput and cost-effectiveness, its application in TDM is limited due to the limitations of the matrixes such as a lack of sensitivity and reproducibility. Here, we present an alternative quantification method for the TDM of the immunosuppressive drugs in the blood of organ transplant patients by utilizing laser desorption ionization mass spectrometry (LDI-MS) based on a tungsten disulfide nanosheet, which is well-known for its excellent physicochemical properties such as a strong UV absorbance and high electron mobility. By adopting a microliquid inkjet printing system, a high-throughput analysis of the blood samples with enhanced sensitivity and reproducibility was achieved. Furthermore, up to 80 cases of patient samples were analyzed and the results were compared with those of LC-MS/MS by using Passing-Bablok regression and Bland-Altman analysis to demonstrate that our LDI-MS platform is suitable to replace current TDM techniques. Our approach will facilitate the rapid and accurate analysis of blood samples from a large number of patients for immunosuppressive drug prescriptions.

A new HPLC-MS/MS method for simultaneous determination of Cyclosporine A, Tacrolimus, Sirolimus and Everolimus for routine therapeutic drug monitoring

A rapid, simple and robust HPLC-MS/MS method for simultaneous determination of immunosuppressants Cyclosporine A, Tacrolimus, Sirolimus and Everolimus has been developed and validated. Sample of whole blood with volume of 50 μL was prepared by a protein precipitation with methanol and 0.5 mol. L^-1 ZnSO₄. Chromatographic separation was achieved on a Phenyl-Hexyl column by a gradient elution using 20 mmol.L^-1 ammonium formate/0.1% (v/v) formic acid in water (mobile phase A) and 20 mmol.L^-1 ammonium formate/0.1% (v/v) formic acid in methanol (mobile phase B) with flow rate 1 mL.min^-1. The run time was 3.5 min. Electrospray ionization and multiple reaction monitoring was used. The lower limit of quantification (LLOQ) was set at 0.5 μg.L^-1 for Tacrolimus, Sirolimus and Everolimus and 5 μg.L^-1 for Cyclosporine A. The method demonstrated adequate accuracy and precision with sufficient linearity range.

HPLC-MS/MS-based analysis of everolimus in rabbit aqueous humor: pharmacokinetics of in situ gel eye drops of suspension

Aim: Everolimus is an inhibitor of mTOR which is derived from rapamycin. Its high corneal permeability and bioavailability makes it an effective treatment for ocular disorders. To study the pharmacokinetics of in situ gel eye drops of everolimus suspension after ocular administration in rabbit aqueous humor, we developed a rapid and reliable HPLC-MS/MS method. Methodology/results: Ascomycin was selected as the internal standard. HPLC-MS/MS method was used to investigate the concentration-time relationship of everolimus in rabbit aqueous humor through protein precipitation technique. The validated results showed good linearity, accuracy and precision. Conclusion: The method developed in this study is rapid, sensitive and reliable for the determination of the concentration of everolimus in rabbit aqueous humor.

Antineoplastic drugs and their analysis: a state of the art review

We provide an overview of the analytical methods available for the quantification of antineoplastic drugs in pharmaceutical formulations, biological and environmental samples.

Therapeutic Drug Monitoring of Everolimus: A Consensus Report

In 2014, the Immunosuppressive Drugs Scientific Committee of the International Association of Therapeutic Drug Monitoring and Clinical Toxicology called a meeting of international experts to provide recommendations to guide therapeutic drug monitoring (TDM) of everolimus (EVR) and its optimal use in clinical practice. EVR is a potent inhibitor of the mammalian target of rapamycin, approved for the prevention of organ transplant rejection and for the treatment of various types of cancer and tuberous sclerosis complex. EVR fulfills the prerequisites for TDM, having a narrow therapeutic range, high interindividual pharmacokinetic variability, and established drug exposure-response relationships. EVR trough concentrations (C0) demonstrate a good relationship with overall exposure, providing a simple and reliable index for TDM. Whole-blood samples should be used for measurement of EVR C0, and sampling times should be standardized to occur within 1 hour before the next dose, which should be taken at the same time everyday and preferably without food. In transplantation settings, EVR should be generally targeted to a C0 of 3-8 ng/mL when used in combination with other immunosuppressive drugs (calcineurin inhibitors and glucocorticoids); in calcineurin inhibitor-free regimens, the EVR target C0 range should be 6-10 ng/mL. Further studies are required to determine the clinical utility of TDM in nontransplantation settings. The choice of analytical method and differences between methods should be carefully considered when determining EVR concentrations, and when comparing and interpreting clinical trial outcomes. At present, a fully validated liquid chromatography tandem mass spectrometry assay is the preferred method for determination of EVR C0, with a lower limit of quantification close to 1 ng/mL. Use of certified commercially available whole-blood calibrators to avoid calibration bias and participation in external proficiency-testing programs to allow continuous cross-validation and proof of analytical quality are highly recommended. Development of alternative assays to facilitate on-site measurement of EVR C0 is encouraged.

Current methods of the analysis of immunosuppressive agents in clinical materials: A review

More than 100000 solid organ transplantations are performed every year worldwide. Calcineurin (cyclosporine A, tacrolimus), serine/threonine kinase (sirolimus, everolimus) and inosine monophosphate dehydrogenase inhibitor (mycophenolate mofetil), are the most common drugs used as immunosuppressive agents after solid organ transplantation. Immunosuppressive therapy, although necessary after transplantation, is associated with many adverse consequences, including the formation of secondary metabolites of drugs and the induction of their side effects. Calcineurin inhibitors are associated with nephrotoxicity, cardiotoxicity and neurotoxicity; moreover, they increase the risk of many diseases after transplantation. The review presents a study of the movement of drugs in the body, including the processes of absorption, distribution, localisation in tissues, biotransformation and excretion, and also their accompanying side effects. Therefore, there is a necessity to monitor immunosuppressants, especially because these drugs are characterised by narrow therapeutic ranges. Their incorrect concentrations in a patient's blood could result in transplant rejection or in the accumulation of toxic effects. Immunosuppressive pharmaceuticals are macrolide lactones, peptides, and high molecular weight molecules that can be metabolised to several metabolites. Therefore the two main analytical methods used for their determination are high performance liquid chromatography with various detection methods and immunoassay methods. Despite the rapid development of new analytical methods of analysing immunosuppressive agents, the application of the latest generation of detectors and increasing sensitivity of such methods, there is still a great demand for the development of highly selective, sensitive, specific, rapid and relatively simple methods of immunosuppressive drugs analysis.

Development and Validation of Stability-indicating High Performance Liquid Chromatographic Method for the Estimation of Everolimus in Tablets

The present study depicts the development of a validated reversed-phase high performance liquid chromatographic method for the determination of the everolimus in presence of degradation products or pharmaceutical excipients. Stress study was performed on everolimus and it was found that it degrade sufficiently in oxidizing and acidic conditions but less degradation was found in alkaline, neutral, thermal and photolytic conditions. The separation was carried out on Hypersil BDS C18 column (100×4.6 mm, 5 μ) column having particle size 5 μ using acetate buffer:acetonitrile (50:50 v/v) with pH 6.5 adjusted with orthophosphoric acid as mobile phase at flow rate of 1 ml/min. The wavelength of the detection was 280 nm. A retention time (R_t) nearly 3.110 min was observed. The calibration curve for everolimus was linear (r²=0.999) from range of 25-150 μg/ml with limit of detection and limit of quantification of 0.036 μg/ml and 0.109 μg/ml, respectively. Analytical validation parameters such as selectivity, specificity, linearity, accuracy and precision were evaluated and relative standard deviation value for all the key parameters were less than 2.0%. The recovery of the drug after standard addition was found to be 100.55%. Thus, the developed RP-HPLC method was found to be suitable for the determination of everolimus in tablets containing various excipients.

Structural characterization of cyclosporin A, C and microbial bio-transformed cyclosporin A analog AM6 using HPLC-ESI-ion trap-mass spectrometry

Cyclosporin A (CyA), a cyclic undecapeptide produced by a number of fungi, contains 11 unusual amino acids, and has been one of the most commonly prescribed immunosuppressive drugs. To date, there are over sixty different analogs reported as congeners and analogs resulting from precursor-directed biosynthesis, human CYP-mediated metabolites, or microbial bio-transformed analogs. However, there is still a need for more structurally diverse CyA analogs in order to discover new biological potentials and/or improve the physicochemical properties of the existing cyclosporins. As a result of the complexity of the resulting mass spectrometric (MS) data caused by its unusual amino acid composition and its cyclic nature, structural characterization of these cyclic peptides based on fragmentation patterns using multiple tandem MS analyses is challenging task. Here, we describe, an efficient HPLC-ESI-ion trap MS(n) (up to MS(8)) was developed for the identification of CyA and CyC, a (Thr(2))CyA congener in which L-aminobutyric acid (Abu) is replaced by L-threonine (Thr). In addition, we examined the fragmentation patterns of a CyA analog obtained from the cultivation of a recombinant Streptomyces venezuelae strain fed with CyA, assigning this analog as (γ-hydroxy-MeLeu(6))CyA (otherwise, known as an human CYP metabolite AM6). This is the first report on both the MS(n)-aided identification of CyC and the structural characterization of a CyA analog by employing HPLC-ESI-ion trap MS(n) analysis.

Comparison of Antibody-Conjugated Magnetic Immunoassay and Liquid Chromatography-Tandem Mass Spectrometry for the Measurement of Cyclosporine and Tacrolimus in Whole Blood

The aim of this work is to compare the results of a commercially available liquid chromatography tandem mass spectrometry (LC-MS/MS) method in a clinical pathology laboratory for routine Therapeutic Drug Monitoring (TDM) of cyclosporine (CsA) and tacrolimus (Tacr) in pediatric patients with those obtained with the current antibody-conjugated magnetic immunoassay (ACMIA). Whole blood levels of CsA (n= 135) and Tacr (n=100) were sequentially analyzed by using ACMIA and LC-MS/MS on pediatric transplanted patients. The differences were analyzed by using the Passing Bablok regression analysis and the Bland and Altman test. The LC-MS/MS method showed excellent reproducibility and lower limits of quantification compared to the ACMIA. A linear relationship between ACMIA and LC-MS/MS was obtained for both CsA (r= 0.9449; P<0.0001, 95% CI 0.9234 to 0.9605) and Tacr (r=0.9275; P<0.0001, 95% CI 0.8941 to 0.9506). No significant inter-method biases were observed. The analytical performances of the LC-MS/MS method make it suitable for the accurate measurement of CsA and Tacr in pediatric transplanted patients. However ACMIA results are also accurate and reliable. For this reason the choice of the method to be used in a routine clinical pathology laboratory can be made on the bases of non-analytical considerations such as costs, organization, availability of skilled personnel.

The current role of liquid chromatography-tandem mass spectrometry in therapeutic drug monitoring of immunosuppressant and antiretroviral drugs

Therapeutic drug monitoring of critical dose immunosuppressant drugs is established clinical practice and there are similar good reasons to monitor antiretrovirals. The aim of this article is to review the recent literature (last five years), with particular reference to the use of liquid chromatography-tandem mass spectrometry (LC-MS/MS). LC-MS/MS offers many potential advantages. The superior selectivity of LC-MS/MS over immunoassays for immunosuppressant drugs has been widely reported. Simultaneous measurement of a number of drugs can be performed. It is currently routine practice for the four major immunosuppressants (cyclosporin, tacrolimus, sirolimus and everolimus) to be simultaneously measured in whole blood. While up to 17 antiretroviral drugs have been simultaneously measured in plasma. The exquisite sensitivity of LC-MS/MS also provides the opportunity to measure these drugs in alternative matrices, such as dried blood spots, saliva, peripheral blood mononuclear cells and tissue. However, the clinical utility of measuring these classes of drugs in alternative matrices is still to be determined.

C-440T/T-331C polymorphisms in the UGT1A9 gene affect the pharmacokinetics of mycophenolic acid in kidney transplantation

INTRODUCTION

The immunosuppressive agent mycophenolic acid (MPA) is metabolized by uridine diphosphate glucuronosyltransferase 1A9 (UGT1A9) to 7-O-glucuronide (MPAG) and excreted by multidrug resistance-associated protein 2 in the bile. By contrast, the production of the acyl MPAG, a minor MPA metabolite, was ascribed to UGT2B7 and UGT1A8. Several polymorphisms in the genes encoding for UGT1A9, UGT2B7 and MRP2 proteins have been described. However, their functional role in vivo on MPA metabolism remains poorly defined.

METHODS

A total of 40 Caucasian kidney transplant patients, given induction therapies (with Campath-(1)H or the combination basiliximab/rabbit antithymocyte globulin) and on maintenance immunosuppression with cyclosporine in combination with mycophenolate mofetil (MMF) in a steroid-free regimen, were enrolled in the pharmacogenetic study. Patients had clinical and hematochemical evaluations at month 6 after transplantation, as well as complete MPA pharmacokinetic assessment. They were genotyped for SNPs in UGT1A9 C-2152T, T-1887G, C-665T, C-440T, T-331C, T-275A, T98C, for the nonsynonymous C802T SNP in UGT2B7, and for ABCC2 SNPs C-24T and G1249A. The association of these polymorphisms with MPA pharmacokinetic parameters was investigated.

RESULTS

Differences in the MPA pharmacokinetic profiles confirmed large interpatient variability of MPA exposure, with AUC(0-12) values ranging from 7.9 to 50.1 mg*h/ml. MPA AUC(0-12) was significantly associated with the presence of UGT1A9 -440/-331 genotypes (TT/CC: 61.5 +/- 2.7 mg*h/ml/g MMF; TC/CT: 45.4 +/- 14.0 mg*h/ml/g MMF; CC/TT: 40.8 +/- 10.8 mg*h/ml/g MMF; p = 0.005), whereas MPAG exposure was mainly influenced by renal function. The positive association between MPA AUC and SNPs in position -440/-331 found in kidney transplant patients confirmed previous in vitro findings showing that the abovementioned SNPs had a significant impact on UGT1A9 protein content in the liver. The presence of ABCC2 promoter C-24T and exon 10 G1249A SNPs did not cause any significant variation in MPA and MPAG pharmacokinetic parameters.

CONCLUSION

The study demonstrated a significant impact of C-440T/T-331C SNPs in the promoter region of the UGT1A9 gene on MPA pharmacokinetics in renal allograft recipients.

Current role of LC-MS in therapeutic drug monitoring

The role of liquid chromatography coupled with mass spectrometry (LC-MS) techniques in routine therapeutic drug monitoring activity is becoming increasingly important. This paper reviews LC-MS methods published in the last few years for certain classes of drugs subject to therapeutic drug monitoring: immunosuppressants, antifungal drugs, antiretroviral drugs, antidepressants and antipsychotics. For each class of compounds, we focussed on the most interesting methods and evaluated the current role of LC-MS in therapeutic drug monitoring.

Comparison of fluorescent polarization immunoassay (FPIA) versus HPLC to measure everolimus blood concentrations in clinical transplantation

Clinical management of transplant patients depends on therapeutic drug monitoring (TDM) and regulation of immunosuppressive therapy. TDM of whole-blood concentrations is mandatory for everolimus (ERL) dosage individualisation. We compared the new semi-automated immunoassay (Innofluor Certican Assay System, Seradyn Inc) using FPIA technology on Abbott TDxFLx analyzers with established HPLC-UV as reference method. A total of 165 samples were analyzed from 52 transplant patients (40 kidney, 12 heart) receiving ERL or another immunosuppressive agent as part their routine care after organ transplantation. The correlation coefficient was r(2)=0.8229, and the regression equation (95% IC) yielded FPIA=1.111 x (HPLC)+0.378. FPIA compared to HPLC gave a positive bias of 1.19 ng/ml. The FPIA assay so appears to have a diagnostic efficacy comparable to HPLC for assessing the risk of acute rejection in transplant recipients. However, the values of the FPIA were higher than those calculated from HPLC measurements, because of the cross-reactivity of the antibody used in the FPIA assay with the ERL metabolite and/or with sirolimus; this cross-reactivity occurs frequently when transplant patients are switched from sirolimus to ERL.

A HPLC–mass spectrometric method suitable for the therapeutic drug monitoring of everolimus

We report here the validation of an HPLC-electrospray-tandem mass spectrometry method for the quantification of everolimus, an immunosuppressant drug. Whole blood samples (100 microl) were extracted by protein precipitation which involved sample pre-treatment with zinc sulphate followed by acetonitrile (containing internal standard, 40-O-(3'-hydroxy)propyl-rapamycin). HPLC was performed using a step-gradient at a flow rate of 0.6 ml/min on a Waters TDM C18 column (10 mm x 2.1mm I.D.) with a resultant chromatographic analysis time of 2 min. Mass spectrometric detection by selected reaction monitoring (everolimus m/z 975.5-->908.3; internal standard m/z 989.5-->922.3). The assay was linear from 0.5 to 40 microg/l (r2>0.994, n=11). The inter- and intra-day analytical recovery and imprecision for quality control samples (1.25, 12.5 and 30 microg/l) were 93.4-98.2% and <10.7%, respectively (n=10). At the lower limit of quantification (0.5 microg/l) the inter- and intra-day analytical recovery was 94.4-95.8% with imprecision of <14.1% (n=10). The absolute recovery of everolimus (6.5 microg/l) and internal standard (12.5 microg/l) was 96.5 and 88.3%, respectively (n=3). A comparison of our method against the mean of all HPLC methods for a series of samples from an external proficiency testing scheme revealed good correlation as shown by the regression analysis: y=0.973x+0.301 (r2=0.986, n=71). In conclusion, the method described is suited to the current requirements for therapeutic drug monitoring of everolimus.

Mycophenolic Acid Formulation Affects Cyclosporine Pharmacokinetics in Stable Kidney Transplant Recipients

A novel monitoring strategy based on the blood concentration at two hours post-dose (C2) has been recently proposed for the assessment of cyclosporine (CsA) absorption and daily exposure, and therapeutic windows for C2 levels have been identified. These guidelines have been derived from patients given mycophenolate mofetil (MMF) or azathioprine, and never tested in those treated with the enteric-coated formulation of mycophenolic acid (EC-MPS). The authors have compared full CsA pharmacokinetic evaluations in 12 kidney transplant recipients given EC-MPS with those from 20 patients on MMF at months 6, 12, 18 and 24 postsurgery. At month 6 postsurgery, patients on EC-MPS had a shift to the right in the CsA peak concentration as compared to that in patients given MMF, an effect associated with significant differences in CsA Tmax (1.9 +/- 0.3 h vs. 1.5 +/- 0.6 h, P < 0.05), C2 (988 +/- 259 vs. 720 +/- 214 ng/mL, P < 0.01), and C3 levels (539 +/- 119 vs. 435 +/- 119 ng/mL, P < 0.05). Interestingly, the authors found that the majority of patients on EC-MPS had CsA peaking at 2-h postdosing, whereas most of patients on MMF had CsA Cmax at 1 h. Similar results were observed also at months 12, 18, and 24 postsurgery. These findings indicate that the pharmacokinetics of CsA is significantly affected by the concomitant administration of different MPA formulations. This would imply the need of specific algorithms to adequately estimate CsA dose adjustment in patients given, in addition to CsA, EC-MPS or MMF.