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Background: Intrapatient variability (IPV) in tacrolimus exposure is associated with renal allograft failure. The aim of this study was to investigate whether conversion from the twice-daily tacrolimus formulation (Tac-TD) to a once-daily formulation (Tac-OD) leads to a lower IPV in tacrolimus exposure., Methods: Two hundred forty-seven stable renal transplant recipients were converted from Tac-TD to Tac-OD (Advagraf) on a 1:1-mg total daily dose basis. After conversion, patients were followed for 12 months and tacrolimus predose whole-blood concentrations (C0), serum creatinine, estimated glomerular filtration rate, and proteinuria were measured. These parameters were compared with those collected at all outpatient visits in the 12-month period (±3 months) before conversion (Tac-TD period). The IPV was calculated based on the dose-adjusted tacrolimus C0., Results: The Tac-OD formulation provided an excellent graft survival (100%), a low acute rejection rate (0.8%), and good tolerability. Renal function remained stable: estimated glomerular filtration rate 48 (16-90) versus 46 (12-90) mL/min (P = 0.15) before and after conversion, respectively. After conversion to Tac-OD, mean C0 was significantly lower, decreasing from 5.7 ± 1.5 to 5.0 ± 1.5 ng/mL, corresponding to a 12% reduction (P < 0.01). Both drugs had similar IPVs (Tac-TD: 17.3% ± 1.6% versus Tac-OD: 16.4% ± 1.6%, P = 0.31)., Conclusions: Although conversion from Tac-TD to Tac-OD significantly reduces tacrolimus exposure as measured by C0 and seems safe, it does not reduce IPV in tacrolimus exposure.

Mycophenolic acid (MPA) has become the cornerstone in the treatment of lupus nephritis. However, response rates are still far from ideal in clinical trials. Uncertainty exists regarding the correct dosing of MPA, and the recommended doses vary between recently published guidelines. Side effects are an additional problem resulting in frequent dose reduction and possible suboptimal exposure.In this review, we discuss the large variability between patients in drug exposure to MPA and the evidence for a relationship between drug exposure and efficacy in lupus nephritis. Methods for drug monitoring of MPA are discussed, and based on the current literature, we suggest as potential target levels a pre-dose level of 3.0 mg/L and an area under the concentration-versus-time curve between 35 and 45 mg h/L.Therapeutic drug monitoring may improve response rates in lupus nephritis by preventing low exposure and at the same time may reduce unnecessary side effects in patients who have high drug exposure with standard dose MPA. We specifically advise assessment of MPA drug exposure early after start of treatment and before concluding that treatment with MPA has failed., (© The Author 2014. Published by Oxford University Press on behalf of ERA-EDTA. All rights reserved.)

Tacrolimus (Tac) is widely used for the prevention of rejection after solid organ transplantation. Finding the optimal balance between effective Tac concentrations and toxicity is a challenge and requires therapeutic drug monitoring. In addition to the well-known inter-patient variability, the clinical use of Tac is also complicated by considerable intra-patient variability (IPV) in Tac exposure. Tac IPV is defined as the amount of fluctuation of whole-blood concentrations over a certain period of time during which the Tac dose remains unchanged. A high IPV in Tac exposure has recently been recognized as a strong risk factor for acute rejection and poor long-term kidney transplantation outcome. In addition to non-adherence, several other factors determine the magnitude of the IPV in Tac exposure. Quantification of IPV is easy and can be easily incorporated into everyday clinical practice as a tool for optimizing transplantation outcomes., (Copyright © 2015 Elsevier Inc. All rights reserved.)

Clinical response to tamoxifen varies widely among women treated with this drug for hormone receptor-positive breast cancer. The principal active metabolite - endoxifen - is generated through hepatic metabolism of tamoxifen, with key roles for cytochrome P450 (CYP) CYP2D6 and CYP3A. By influencing endoxifen formation, genetic variants of CYP2D6 may affect response to tamoxifen. After a decade of research, examining the effects of CYP2D6 genetic variants on tamoxifen efficacy, there is still no agreement on the clinical utility of CYP2D6 genotype as biomarker for the prediction of breast cancer outcome, because studies revealed conflicting results. However, tamoxifen metabolism is complex and involves several other drug-metabolizing enzymes. Genetic variants of other CYP enzymes, including CYP3A4 and CYP2C9/19, as well as co-medication interfering with the metabolic activity of CYP2D6 and CYP3A4 have been shown to affect endoxifen concentrations and may also contribute to the variability in response to tamoxifen. Phenotyping strategies can predict endoxifen exposure more accurately than CYP2D6 genotype, but do not take into account all factors influencing endoxifen exposure. Therapeutic drug monitoring (TDM) is likely to be the optimal strategy for individualization of tamoxifen treatment. According to a growing amount of literature, endoxifen concentration seems to be a predictor of clinical outcome. The relationship between endoxifen levels and breast cancer outcomes has to be replicated and confirmed and the value of TDM should be evaluated in prospective clinical trials. Caution is advised regarding the concomitant use of medications which could interact with tamoxifen, including inhibitors and inducers of CYP enzymes., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

Background: Nonadherence to immunosuppressive medication after kidney transplantation is a behavioral issue and as such it is important to understand the psychological factors that influence this behavior. The aim of this study was to investigate the extent to which goal cognitions, illness perceptions, and treatment beliefs were related to changes in self-reported immunosuppressive medication adherence up to 18 months after transplantation., Methods: Interviews were conducted with patients in the outpatient clinic 6 weeks (T1; n=113), 6 months (T2; n=106), and 18 months (T3; n=84) after transplantation. Self-reported adherence was measured using the Basel Assessment of Adherence to Immunosuppressive Medications Scale Interview. Psychological concepts were measured using the Brief Illness Perceptions Questionnaire, Beliefs about Medicines Questionnaire, and questions on the importance of adherence as a personal goal, conflict with other goals, and self-efficacy for goal attainment., Results: Nonadherence significantly increased over time to 31% at T3. Perceived necessity of medication, perceived impact of transplant on life (consequences) and emotional response to transplantation significantly decreased over time. Participants who reported low importance of medication adherence as a personal goal were more likely to become nonadherent over time., Conclusions: Illness perceptions can be described as functional and supportive of adherence which is inconsistent with the pervasive and increasing nonadherence observed. There appears therefore to be a discrepancy between beliefs about adherence and actual behavior. Promoting (intrinsic) motivation for adherence goals and exploring the relative importance in comparison to other personal goals is a potential target for interventions.

Background: Several lines of evidence suggest a T cell-mediated immune response in paraneoplastic neurological syndromes with anti-Hu antibodies (Hu-PNS). In order to investigate whether suppression of T cell-mediated immune responses in Hu-PNS patients improved their neurological outcome, we performed a prospective open-label, single-arm study on sirolimus., Methods: Seventeen progressive Hu-PNS patients were treated with sirolimus with an intended treatment duration of 8 weeks. Primary outcome measures were (i) functional improvement, defined as a decrease of one or more points on the modified Rankin Scale (mRS), and (ii) improvement of neurological impairment, defined as an increase of one or more points on the Edinburgh Functional Impairment Tests (EFIT)., Results: One patient showed improvement on both clinical scales (mRS and EFIT). This patient presented with limbic encephalitis and improved dramatically from an mRS score of 3 to mRS 1. Another patient, with subacute sensory neuronopathy, remained stable at mRS 2 and improved one point on the EFIT scale. The other patients showed no improvement on the primary outcome measures. Median survival was 21 months., Conclusion: We conclude that treatment of Hu-PNS patients with sirolimus may improve or stabilize their functional disabilities and neurological impairments. However, the effects of this T cell-targeted therapy were not better than reported in trials on other immunotherapies for Hu-PNS. Trial Registration https://www.clinicaltrialsregister.eu/ctr-search/trial/2008-000793-20/NL., (© The Author(s) 2014. Published by Oxford University Press on behalf of the Society for Neuro-Oncology. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

The transplantation literature includes numerous papers that report associations between polymorphisms in genes encoding metabolizing enzymes and drug transporters, and pharmacokinetic data on immunosuppressive drugs. Most of these studies are retrospective in design, and although a substantial number report significant associations, pharmacogenetic tests are hardly used in clinical practice. One of the reasons for this poor implementation is the current lack of evidence of improved clinical outcome with pharmacogenetic testing. Furthermore, with efficient therapeutic drug monitoring it is possible to rapidly correct for the effect of genotypic deviations on pharmacokinetics, thereby decreasing the utility of genotype-based dosing. The future of pharmacogenetics will be in treatment models in which patient characteristics are combined with data on polymorphisms in multiple genes. These models should focus on pharmacodynamic parameters, variations in the expression of drug transporter proteins, and predictors of toxicity. Such models will provide more information than the relatively small candidate gene studies performed so far. For implementation of these models into clinical practice, linkage of genotype data to medication prescription systems within electronic health records will be crucial.

This overview describes the full spectrum of current pre-clinical and clinical kidney-, liver-, heart- and lung transplantation research performed in Erasmus MC - University Medical Centre in Rotterdam, The Netherlands. An update is provided on the development of a large living donor kidney transplantation program and on optimization of kidney allocation, including the implementation of a domino kidney-donation program. Our current research efforts to optimize immunosuppressive regimens and find novel targets for immunosuppressive therapy, our recent studies on prevention of ischemia-reperfusion-induced graft injury, our newest findings on stimulation of tissue regeneration, our novel approaches to prevent rejection and viral infection, and our latest insights in the regulation of allograft rejection, are summarized., (Copyright © 2014 Elsevier B.V. All rights reserved.)

Mycophenolate mofetil (MMF) is used to prevent acute rejection following solid organ transplantation in transplant centers all over the world. Patients from different ethnic backgrounds are treated with this drug, for which therapeutic drug monitoring (TDM) has not become the standard of practice in most centers. Whether or not some ethnic groups require a different MMF dose has been a topic of debate in recent years. In this review, it is shown that Asian patients, compared with Caucasian patients, with a comparable MMF dose reach higher mycophenolic acid (MPA) exposure. Also clinical experience points toward more adverse events in case of treatment with 1 g MMF bid in Asian patients, and therefore, for this ethnic group, a lower maintenance dose seems justified. In contrast, African American patients reach similar drug concentrations as Caucasians patients receiving the same MMF dose, but due to immunological reasons, they require a higher MMF dose to reach comparable acute rejection incidences. When TDM is performed, clinicians can correct the dose and compensate for interethnic differences in drug exposure. Otherwise, it is important to choose the right dose. This optimal dose is 20-46% lower in Asian transplant recipients than in Caucasian or African American patients., (© 2014 Steunstichting ESOT.)

Introduction: Chronic kidney disease (CKD) after liver transplantation (LT) is a major clinical problem that appears to be associated with nongenetic as well as genetic determinants. Calcineurin inhibitor (CNI) use is considered to play a major role in the development of CKD after LT. We studied the influence of single-nucleotide polymorphisms (SNPs) in the genes of the donor and recipient CNI-metabolizing enzyme CYP3A5 and the CNI-transporting ABCB1 on the development of CKD after LT., Materials and Methods: Tacrolimus (Tac) predose concentrations at different time-points after transplantation and the CYP3A5 6986A>G and ABCB1 3435C>T SNPs were determined in 125 LT recipients and their respective donors to study the influence of Tac predose levels and genetics on the development of CKD., Results: After a median follow-up of 5.7±2.9 years, CKD developed in 47 patients (36%). The Tac predose levels were not correlated with the development of CKD. Neither did we find a correlation between the investigated SNPs in either donor or recipient ABCB1 and CYP3A5 genes (or combinations thereof) and the development of CKD. These genetic variations did not relate to Tac predose blood concentrations in our study., Conclusion: An individual's risk of developing CKD after LT is not associated with genetic variation in either recipient or donor CYP3A5 or ABCB1 genotype status.

Background: Calcineurin inhibitors (CNIs) are essential immunosuppressive drugs after renal transplantation. Because of nephrotoxicity, withdrawal has been a challenge since their introduction., Methods: A randomized multicenter trial included 212 kidney patients transplanted between 1997 and 1999. All patients were initially treated with mycophenolate mofetil (MMF), cyclosporine A (CsA), and prednisone (pred). At 6 months after transplantation, 63 patients were randomized for MMF/pred, 76 for MMF/CsA, and 73 for MMF/CsA/pred. Within 18 months after randomization 23 patients experienced a rejection episode: MMF/pred (27.0%), MMF/CsA (6.8%) and MMF/CsA/pred (1.4%) (P<0.001)., Results: During 15 years of follow-up, 73 patients died with a functioning graft, and 43 patients lost their graft. Ninety-six were alive with a functioning graft. Intention-to-treat analysis did not show a significant difference in patient and graft survival. In multivariate analysis, death-censored graft survival was significantly associated with serum creatinine at 6 months after transplantation and maximum PRA but not with the randomization group. CNI withdrawal did not result in a reduced incidence of or death by malignancy or cardiovascular disease. Death-censored graft survival was significantly worse in those patients randomized for CNI withdrawal that had to be reverted to CNI. Independent of randomization group, compared with no rejection, death-censored graft survival was significantly worse in 23 patients with acute rejection after randomization., Conclusion: Fifteen years after conversion to a CNI free regimen, there was no benefit regarding graft and patient survival or regarding prevalence of or death by comorbidities. However, rejection shortly after CNI withdrawal was associated with decreased graft survival.

In the past decade, many tyrosine-kinase inhibitors have been introduced in oncology and haemato-oncology. Because this new class of drugs is extensively used, serious drug-drug interactions are an increasing risk. In this Review, we give a comprehensive overview of known or suspected drug-drug interactions between tyrosine-kinase inhibitors and other drugs. We discuss all haemato-oncological and oncological tyrosine-kinase inhibitors that had been approved by Aug 1, 2013, by the US Food and Drug Administration or the European Medicines Agency. Various clinically relevant drug interactions with tyrosine-kinase inhibitors have been identified. Most interactions concern altered bioavailability due to altered stomach pH, metabolism by cytochrome P450 isoenzymes, and prolongation of the QTc interval. To guarantee the safe use of tyrosine-kinase inhibitors, a drugs review for each patient is needed. This Review provides specific recommendations to guide haemato-oncologists, oncologists, and clinical pharmacists, through the process of managing drug-drug interactions during treatment with tyrosine-kinase inhibitors in daily clinical practice., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

Within-patient variability in immunosuppressive drug exposure is easily identified by measurement of drug concentrations at the outpatient clinic. Fluctuating levels despite a stable drug dose can be observed in a substantial proportion of patients. It has now been shown that this within-patient variability is a predictor for poor long-term outcome after transplantation. Nonadherence most likely is an important determinant of variability, and strategies to tackle nonadherence are being developed.

Acute rejection (AR) remains a concern for kidney transplantation. Cytokines are key mediators in the induction and effector phases of all immune and inflammatory responses. Single nucleotide polymorphisms (SNPs) in cytokines and their receptors may relate to AR. We investigated the relation between AR and SNPs in the genes encoding for IL-2(-330G>T), IL-10(-592C>A and -1082G>A), TGF-β1(915G>C), and IL-2RB(rs228942 C>A and rs228953 C>T) in 325 renal transplant patients during the first year after transplantation. The overall incidence of AR was 15.4%. In multivariate analysis, only the use of induction therapy was correlated with AR (odds ratio 1.9; 95% confidence interval 1.1-3.7; p = 0.04). No statistically significant associations between the SNPs studied and AR were observed. SNPs in the investigated cytokines and their receptors were not associated with the risk of AR. Genotyping patients for these SNPs is unlikely to aid the clinician in adjusting the immunosuppressive therapy for individual patients., (© 2014 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Hypertension is a common side effect of calcineurin inhibitors (CNIs), which are drugs used to prevent rejection after transplantation. Hypertension after kidney transplantation has been associated with earlier graft failure and higher cardiovascular mortality in the recipient. Recent data indicate that enzymes and transporters involved in CNI pharmacokinetics and pharmacodynamics, including CYP3A5, ABCB1, WNK4 and SPAK, are also associated with salt-sensitive hypertension. These insights raise the question whether polymorphisms in the genes encoding these proteins increase the risk of CNI-induced hypertension. Predicting who is at risk for CNI-induced hypertension may be useful for when selecting specific interventions, including dietary salt restriction, thiazide diuretics or a CNI-free immunosuppressive regimen. This review aims to explore the pharmacogenetics of CNI-induced hypertension, highlighting the knowns and unknowns.

Pharmacogenetics has generated many expectations for its potential to individualize therapy proactively and improve medical care. However, despite the huge amount of reported genetic associations with either pharmacokinetics or pharmacodynamics of drugs, the translation into patient care is still slow. In fact, strong evidence for a substantial clinical benefit of pharmacogenetic testing is still limited, with a few exceptions. In kidney transplantation, established pharmacogenetic discoveries are being investigated for application in the clinic to improve efficacy and to limit toxicity associated with the use of immunosuppressive drugs, especially the frequently used calcineurin inhibitors (CNIs) tacrolimus and ciclosporin. The purpose of the present review is to picture the current status of CNI pharmacogenetics and to discuss the most promising leads that have been followed so far., (© 2013 The British Pharmacological Society.)

Implementation of pharmacogenetics in transplantation medicine has not met the expectations expressed 15 years ago. Numerous studies have reported associations between gene polymorphisms and pharmacokinetics of immunosuppressive drugs. Evidence that genotype-based dosing improves outcome is lacking. Extensive therapeutic drug monitoring (TDM) can rapidly correct for the variability in drug exposure caused by genetic differences. The contribution of genotype-based dosing will be more pronounced for drugs for which pharmacokinetic or pharmacodynamic monitoring is not applied.

The calcineurin inhibitor tacrolimus is the backbone of immunosuppressive drug therapy after solid organ transplantation. Tacrolimus is effective in preventing acute rejection but has considerable toxicity and displays marked inter-individual variability in its pharmacokinetics and pharmacodynamics. The genetic basis of these phenomena is reviewed here. With regard to its pharmacokinetic variability, a single nucleotide polymorphism (SNP) in cytochrome P450 (CYP) 3A5 (6986A>G) has been consistently associated with tacrolimus dose requirement. Patients expressing CYP3A5 (those carrying the A nucleotide, defined as the *1 allele) have a dose requirement that is around 50 % higher than non-expressers (those homozygous for the G nucleotide, defined as the *3 allele). A randomised controlled study in kidney transplant recipients has demonstrated that a CYP3A5 genotype-based approach to tacrolimus dosing leads to more patients reaching the target concentration early after transplantation. However, no improvement of clinical outcomes (rejection incidence, toxicity) was observed, which may have been the result of the design of this particular study. In addition to CYP3A5 genotype, other genetic variants may also contribute to the variability in tacrolimus pharmacokinetics. Among these, the CYP3A4*22 and POR*28 SNPs are the most promising. Individuals carrying the CYP3A4*22 T-variant allele have a lower tacrolimus dose requirement than individuals with the CYP3A4*22 CC genotype and this effect appears to be independent of CYP3A5 genotype status. Individuals carrying the POR*28 T-variant allele have a higher tacrolimus dose requirement than POR*28 CC homozygotes but this association was only found in CYP3A5-expressing individuals. Other, less well-defined SNPs have been inconsistently associated with tacrolimus dose requirement. It is envisaged that in the future, algorithms incorporating clinical, demographic and genetic variables will be developed that will aid clinicians with the determination of the tacrolimus starting dose for an individual transplant recipient. Such an approach may limit early tacrolimus under-exposure and toxicity. With regard to tacrolimus pharmacodynamics, no strong genotype-phenotype relationships have been identified. Certain SNPs associate with rejection risk but these observations await replication. Likewise, the genetic basis of tacrolimus-induced toxicity remains unclarified. SNPs in the genes encoding for the drug transporter ABCB1 and the CYP3A enzymes may relate to chronic nephrotoxicity but findings have been inconsistent. No genetic markers reliably predict new-onset diabetes mellitus after transplantation, hypertension or neurotoxicity. The CYP3A5*1 SNP is currently the most promising biomarker for tailoring tacrolimus treatment. However, before CYP3A5 genotyping is incorporated into the routine clinical care of transplant recipients, prospective clinical trials are needed to determine whether such a strategy improves patient outcomes. The role of pharmacogenetics in tacrolimus pharmacodynamics should be explored further by the study of intra-lymphocyte and tissue tacrolimus concentrations.

Background: The P450 oxidoreductase (POR)*28 variant allele has been associated with altered cytochrome P450 3A enzyme activities. Both CYP3A5 and CYP3A4 are involved in the metabolism of calcineurin inhibitors and recent data show that POR*28 may explain part of the variability observed in tacrolimus (Tac) pharmacokinetics. The aim of this study was to investigate the impact of the POR*28 allele on Tac and cyclosporine A (CsA) immunosuppressive therapies., Methods: Kidney transplant recipients receiving either Tac (n = 184) or CsA (n = 174), participating in a prospective multicenter trial, were genotyped for POR*28, CYP3A4*22, and CYP3A5*3., Results: CYP3A5 expressers that were carriers of at least 1 POR*28 allele had a 16.9% decrease in dose-adjusted predose concentrations when compared CYP3A5 expressers that carried the POR*1/*1 genotype (P = 0.03), indicating an increased CYP3A5 activity for POR*28 carriers. In CYP3A5, nonexpressers carrying 2 POR*28 alleles, a 24.1% (confidence interval95% = -39.4% to -4.9%; P = 0.02) decrease in dose-adjusted predose concentrations was observed for Tac, suggesting higher CYP3A4 activity. For CsA, POR*28/*28 patients not expressing CYP3A5 and not carrying the CYP3A4*22 decrease-of-function allele showed 15% lower CsA dose-adjusted predose concentrations (P = 0.01), indicating also increased CYP3A4 activity. In both cohorts (ie, Tac and CsA), the POR*28 allele was neither associated with the incidence of delayed graft function nor with biopsy-proven acute rejection. These results were further confirmed in 2 independent cohorts., Conclusions: Our results show that the POR*28 allele is associated with increased in vivo CYP3A5 activity for Tac in CYP3A5 expressers, whereas POR*28 homozygosity was associated with a significant higher CYP3A4 activity in CYP3A5 nonexpressers for both Tac and CsA.

Mycophenolic acid (MPA) has a low therapeutic index and large inter-individual pharmacokinetic variability necessitating therapeutic drug monitoring to individualise dosing after transplantation. There is an ongoing discrepancy as to whether plasma MPA concentrations sufficiently predict kidney rejection or toxicity and whether immunosuppressant concentrations within the graft tissue may better predict transplant outcomes. The aim of the study was to develop an LC-MS/MS method for the quantification of MPA concentrations in human kidney biopsies taken as part of routine clinical procedures. A total of 4 surplus human kidney biopsies obtained from 4 different kidney transplant recipients were available to use for this study. MPA was also quantified in 2 kidney samples from rats administered MPA to assess tissue extraction reproducibility. Human kidney biopsies and rat kidneys were homogenised mechanically and underwent liquid-liquid extraction before analysis by LC-MS/MS. MPA-free human kidney tissue was used in calibrators and quality control samples. Analyte detection was achieved from multiple reaction monitoring of the ammonium adducts of both MPA (m/z 321.1→207.3) and N-phthaloyl-l-phenylalanine (PPA, internal standard, m/z 296.2→250.2) using positive electrospray ionisation. The method was linear (calibration curves R(2)>0.99, n=10), precise, and accurate with coefficients of variation and bias less than 15%. Extraction efficiencies for MPA and PPA were approximately 97% and 86%, respectively, and matrix effects were minimal. In 4 kidney transplant recipients, tissue MPA concentrations ranged from 1.3 to 7.7ng/mg of tissue, however, the correlation between blood (C0) and tissue MPA concentrations could not be established. The method was successfully applied to the quantification of MPA in human kidney biopsies without the need to alter current clinical protocols., (Copyright © 2013 Elsevier B.V. All rights reserved.)

Background. Nonadherence to medication is a common problem after kidney transplantation. The aim of this study was to explore attitudes towards medication, adherence, and the relationship with clinical outcomes. Method. Kidney recipients participated in a Q-methodological study 6 weeks after transplantation. As a measure of medication adherence, respondents completed the Basel Assessment of Adherence to Immunosuppressive Medications Scale (BAASIS(©)-interview). Moreover, the intrapatient variability in the pharmacokinetics of tacrolimus was calculated, which measures stability of drug intake. Data on graft survival was retrieved from patient records up to 2 years after transplantation. Results. 113 renal transplant recipients (19-75 years old) participated in the study. Results revealed three attitudes towards medication adherence-attitude 1: "confident and accurate," attitude 2: "concerned and vigilant," and attitude 3: "appearance oriented and assertive." We found association of attitudes with intrapatient variability in pharmacokinetics of tacrolimus, but not with self-reported nonadherence or graft survival. However, self-reported nonadherence immediately after transplantation was associated with lower two-year graft survival. Conclusion. These preliminary findings suggest that nonadherence shortly after kidney transplantation may be a risk factor for lower graft survival in the years to follow. The attitudes to medication were not a risk factor.

Background: New-onset diabetes after transplantation (NODAT) is an important complication after kidney transplantation. The etiology of the malady is multifactorial and includes both environmental and genetic factors. NODAT is a polygenic disease and many single-nucleotide polymorphisms could constitute potential risk factors. Peroxisome proliferator-activated receptor α (PPARα) and P450 oxidoreductase (POR) play a central role in the control of energy metabolism in humans. Some recent data highlighted a possible functional impact of two single-nucleotide polymorphisms in PPARα (rs4253728 G>A and rs4823613 A>G) and one coding variant in POR (rs1057868; POR*28; A503V) on the activity of their respective encoded proteins. In the present study, we assessed the association between these variants and the risk of developing NODAT after kidney transplantation., Methods: Development of NODAT was investigated in 101 renal transplant recipients receiving tacrolimus-based immunosuppressive therapy. Patients were genotyped for PPARα and POR. The incidence of NODAT was compared between different genotypes. Kaplan-Meier and Cox's proportional-hazard analysis were used to evaluate the association of NODAT with potential risk factors. Potential nongenetic risk factors were also considered., Results: The PPARα rs4253728A>G and POR*28 variant alleles were both independently associated with an increased risk for NODAT with respective odds ratios of 8.6 [95% confidence interval (CI)=1.4-54.2; P=0.02] and 8.1 (95% CI=1.1-58.3; P=0.04). Other risk predictors included sex and body weight., Conclusion: This candidate-gene study shows that polymorphisms in PPARα and POR might predispose patients being treated with tacrolimus to the development of NODAT after kidney transplantation. Patient management after organ transplantation might benefit from genotype data.

Background: There is scant information on the prevalence and factors associated with preoperative anemia in patients undergoing transcatheter aortic valve implantation (TAVI) and whether it is associated with mortality. We sought to determine the prevalence and factors associated with preoperative anemia in addition to the prognostic effects of the various levels of preoperative hemoglobin level on mortality in patients undergoing TAVI., Methods and Results: Ten-center observational study encompassing 1696 patients with aortic stenosis who underwent TAVI was conducted. Anemia was defined by the World Health Organization criteria (hemoglobin <12.0 g/dL in women and <13.0 g/dL in men). The prevalence of preoperative anemia was 57%. Patient-related factors associated with preoperative anemia were (descending order of odds ratio [95% confidence interval]) as follows: anemia-related medication (4.90 [3.08-7.80]), history of heart failure (1.77 [1.43-2.20]), male sex (1.69 [1.32-2.16]), mitral regurgitation grade ≥III (1.61 [1.15-2.25]), history of malignancy (1.44 [1.03-2.09]), and peripheral vascular disease (1.33 [1.04-1.70]). The creatinine clearance was inversely associated with preoperative anemia (odds ratio, 0.92 [0.87-0.97]). In multivariable analyses, preoperative anemia was not associated with 30-day mortality (1.72 [0.96-3.12]; P=0.073) but showed the strongest association with 1-year mortality with a hazard ratio (95% confidence interval) of 2.78 (1.60-4.82) in patients with hemoglobin <10 g/dL. Patients with anemia received ≥1 blood transfusion 2× more often, but the indication of transfusion was unrelated to overt bleeding in 60%. Blood transfusion was associated with mortality at 30 days (odds ratio, 1.25 [95% confidence interval, 1.08-3.67]) and during follow-up (hazard ratio, 1.09 [95% confidence interval, 1.03-1.14])., Conclusions: Preoperative anemia is prevalent in >50% of patients undergoing TAVI. Various baseline factors were related to anemia, which in turn was associated with 1-year mortality. Patients with anemia received more transfusions but mostly for indications unrelated to overt bleeding, whereas transfusion was independently associated with both early and 1-year mortality. These findings indicate that optimization of baseline factors related to preoperative anemia, in addition to more strict criteria of the use of blood products, may improve outcome after TAVI.

An increasing number of antigen-specific biologics have been introduced into clinical practice, and the ones that arrived first have already reached the end of their patented life span. Despite the use of these agents for over a decade, individualized dosing is not standard practice. Most patients are treated according to treatment protocols, with a fixed dose administered at fixed time intervals. Although the between-subject variability in the volume of distribution is small, there is a moderate to high between-subject variability in the clearance of these biologics. The formation of neutralizing antidrug antibodies (ADAs) further contributes to the variability in the pharmacokinetics and pharmacodynamics. After the development of assays to detect biologic drug serum concentrations and ADA titers, the first clinical studies in immune-mediated diseases such as rheumatology, gastroenterology, and dermatology have now shown clear concentration-effect relationships. By monitoring the serum trough concentrations of biologics, patients with high drug exposure could be identified and dose reductions in those patients may lead to improved safety and substantial cost savings. Low biologic drug serum concentrations may be due to the development of ADAs, and if these are detected, a switch to an alternative treatment is indicated. We envision a vast expansion of therapeutic drug monitoring to support the use of biologics, and we urge the International Association of Therapeutic Drug Monitoring and Clinical Toxicology to embark on initiatives to investigate the contribution of therapeutic drug monitoring to this field.

Background: Tacrolimus (TAC) has a narrow therapeutic index and high interindividual and intraindividual pharmacokinetic variability, necessitating therapeutic drug monitoring to individualize dosage. Recent evidence suggests that intragraft TAC concentrations may better predict transplant outcomes. This study aimed to develop a method for the quantification of TAC in small biopsy-sized samples of rat kidney and liver tissue, which could be applied to clinical biopsy samples from kidney transplant recipients., Methods: Kidneys and livers were harvested from Mrp2-deficient TR- Wistar rats administered TAC (4 mg·kg·d for 14 days, n = 8) or vehicle (n = 10). Tissue samples (0.20-1.00 mg of dry weight) were solubilized enzymatically and underwent liquid-liquid extraction before analysis by liquid chromatography tandem mass spectrometry method. TAC-free tissue was used in the calibrator and quality control samples. Analyte detection was accomplished using positive electrospray ionization (TAC: m/z 821.5 → 768.6; internal standard ascomycin m/z 809.3 → 756.4)., Results: Calibration curves (0.04-2.6 μg/L) were linear (R > 0.99, n = 10), with interday and intraday calibrator coefficients of variation and bias <17% at the lower limit of quantification and <15% at all other concentrations (n = 6-10). Extraction efficiencies for TAC and ascomycin were approximately 70%, and matrix effects were minimal. Rat kidney TAC concentrations were higher (range 109-190 pg/mg tissue) than those in the liver (range 22-53 pg/mg of tissue), with median tissue/blood concentrations ratios of 72.0 and 17.6, respectively. In 2 transplant patients, kidney TAC concentrations ranged from 119 to 285 pg/mg of tissue and were approximately 20 times higher than whole blood trough TAC concentrations., Conclusions: The method displayed precision and accuracy suitable for application to TAC measurement in human kidney biopsy tissue.

Objective: Nonadherence to immunosuppressive medication (IM) after kidney transplantation is related to poorer patient and graft outcomes; therefore research into modifiable factors associated with nonadherence is a priority. In this prospective cohort study we investigated whether changes in goal cognitions, illness perceptions, and treatment beliefs were related to self-reported medication adherence six months after kidney transplantation., Methods: Interviews were conducted with patients in the out-patient clinic six weeks (T1: n=113) and six months (T2: n=106) after transplantation. Self-reported adherence was measured using the Basel Assessment of Adherence to Immunosuppressive Medications Scale (BAASIS© Interview). The Brief Illness Perceptions Questionnaire, Beliefs about Medicines Questionnaire and questions on goal cognitions were also administered at both time points., Results: Self-reported nonadherence increased significantly between 6 weeks and 6 months after transplantation from 17% to 27%. Importance of medication adherence as a personal goal and self-efficacy to successfully carry out this goal decreased significantly over time. Perceived necessity of immunosuppressive medication was high but significantly decreased over time. Concerns about the medicines were low. There were no significant changes in illness perceptions or concerns over time. An increase in perceived graft longevity (timeline) was related to higher likelihood of nonadherence six months post-transplant. Furthermore, younger adult patients were more likely to be nonadherent six months after transplantation., Conclusion: The self-reported nonadherence levels found in this study so soon after transplantation demonstrate the need for early and continued intervention after kidney transplantation in order to maximise adherence and consequently clinical outcomes. Changes in (unrealistic) beliefs regarding the longevity of the graft may offer a potential target for intervention among nonadherent patients., (© 2013.)

Within the field of solid organ transplantation, the patents for a number of immunosuppressive drugs have expired in the last few years. Tacrolimus, cyclosporine, and mycophenolate mofetil are now available as generic drugs. In some countries, the market penetration of these generic formulations is as high as 70%, whereas in some other countries, this figure is below 10%. Several professional societies have published position papers on the risks and benefits of generic substitution of immunosuppressive drugs. It often appears that transplant professionals are not fully aware of the requirements for registration of generic drugs. This article describes the registration requirements with a focus on bioequivalence testing, the strengths and weaknesses in this process, and the differences between Europe and the US., (© 2013 The Authors Transplant International © 2013 European Society for Organ Transplantation. Published by Blackwell Publishing Ltd.)

Objective: To determine the variability of serum IgG in patients with chronic inflammatory demyelinating polyneuropathy (CIDP)., Methods: All 25 CIDP patients had active but stable disease and were treated with individually optimised fixed dose IVIg regimens. IgG was measured by turbidimetry and variability was defined as coefficient of variation (CV)., Results: The intra-patient variability of the pre-treatment IgG levels, post-treatment levels and increase in serum IgG shortly after IVIg (ΔIgG) was low (mean CV=3%, 4%, 10%). The inter-patient variability between patients treated with the same dose and interval was low in pre-treatment, post-treatment and ΔIgG level (mean CV=13%, 11%, 20%). The ΔIgG levels were associated with IVIg dosage (rs=0.78, p<0.001)., Conclusions: Clinically stable CIDP patients show a steady-state in serum IgG after serial IVIg infusions. The low intra- and inter-patient variability in IgG may indicate that constant levels are required to reach this stability.

Introduction: Tacrolimus has a large interindividual pharmacokinetic variability, and quantification of its effect is difficult. It is a substrate of ABCB1, an efflux pump expressed more on CD8 T cells than on CD4 T cells. The ABCB1 3435C>T single-nucleotide polymorphism (SNP) has been associated with interindividual differences in ABCB1 activity and may influence drug efficacy. Here the influence of this SNP on the biological effect of tacrolimus was studied., Methods: Rhodamine (Rh123) efflux was used to study ABCB1 activity, with or without the addition of the ABCB1 inhibitor verapamil. Intracellular interleukin (IL) 2 production in T cells was used to measure the pharmacodynamic effect of tacrolimus after phorbol-12-myristate-13-acetate/ionomycin stimulation of whole blood. In addition, the ABCB1 genotype of 36 tacrolimus-treated renal transplant patients was related to ABCB1 activity and tacrolimus efficacy., Results: The mean Rh123 efflux was higher in CD8 T cells compared with CD4 T cells: 40% versus 19% of cells, respectively (P < 0.001). Verapamil almost completely blocked Rh123 efflux (to 1.8% of CD4 T cells and 0.5% of CD8 T cells), whereas tacrolimus did not change Rh123 efflux. Tacrolimus 10 ng/mL reduced the production of IL-2 in CD4 and CD8 T cells by 28.9% and 45.4% (P < 0.05). Tacrolimus-mediated inhibition of IL-2 was enhanced by verapamil (P < 0.05). This effect on tacrolimus pharmacodynamics was associated with ABCB1 3435C>T SNP in renal transplant patients: verapamil reduced the percentage of IL-2-producing CD4 and CD8 T cells by 14% and 22% in patients with the CC genotype (P < 0.05) but not in patients with the TT genotype. Moreover, the ratio of tacrolimus C0 over the percent of IL-2-producing CD8 T cells in CC genotype patients was significantly higher compared with TT genotype patients (P < 0.05), showing a smaller pharmacodynamic effect in CC genotype patients., Conclusion: The ABCB1 3435C>T SNP influences ABCB1 activity of T cells and the pharmacodynamic effect of tacrolimus in kidney transplant patients.

Background: Prednisolone (PLN) is a widely used corticosteroid in a variety of immune-mediated diseases. Treatment regimes generally consist of empirically derived treatment doses, whereas therapeutic response among patients is highly variable. Drug monitoring of serum PLN levels might support a more rational approach to dose selection, yet is invasive and laborious. In analogy to cortisol, salivary PLN may offer a good alternative for serum PLN, being a representative approximation of free serum PLN. The aims of this study were to evaluate the correlation between free serum and salivary PLN levels and to quantify this relationship within a population pharmacokinetic model., Methods: PLN and prednisone (PN) concentrations were measured in 396 samples from 19 healthy volunteers after oral ingestion of 80 mg PLN. Measurements in serum, ultrafiltrate, and saliva were performed with a recently validated liquid chromatography tandem mass spectrometry method. Population pharmacokinetic analysis was performed with nonlinear mixed effect modeling using NONMEM., Results: Salivary PLN levels correlated well with free serum PLN levels (r = 0.931, P < 0.01). A weaker correlation was found for PN (r = 0.318, P < 0.01), which may be explained by the finding that salivary PN levels mainly seemed to consist of PLN enzymatically converted to PN. Total and free serum PLN concentrations decreased over time after drug administration and showed a nonlinear mutual relationship, consistent with concentration-dependent protein binding. Modeled PLN pharmacokinetics corresponded with previous reports. Low to moderate interindividual variability was found for V/F and CL/F (coefficients of variation were 13.8% and 14.6%, respectively). Free and salivary PLN showed a nonlinear relationship with total PLN. An equation predicting free serum levels from salivary levels was successfully derived from the data., Conclusions: This study is the first to describe the relationship between salivary and (free) serum PLN using a population pharmacokinetic model. Salivary PLN was found to be a reliable predictor of free and total serum PLN in healthy volunteers. The results of this study encourage further exploration of the use of saliva as a noninvasive and feasible method for drug monitoring of PLN.

Tamoxifen is a largely inactive pro-drug, requiring metabolism into its most important metabolite endoxifen. Since the cytochrome P450 (CYP) 2D6 enzyme is primarily involved in this metabolism, genetic polymorphisms of this enzyme, but also drug-induced CYP2D6 inhibition can result in considerably reduced endoxifen formation and as a consequence may affect the efficacy of tamoxifen treatment. Selective serotonin reuptake inhibitors (SSRIs) and selective serotonin and norepinephrine reuptake inhibitors (SNRIs) have been effectively used for the treatment of depression and hot flashes, both of which occur frequently in tamoxifen-treated women. Due to the drug-drug interaction considerably reduced endoxifen concentrations by inhibition of CYP2D6 will be the result. Evidence of a significant influence of strong CYP2D6-inhibiting drugs on the pharmacokinetics of tamoxifen has resulted in recommendations to avoid potent CYP2D6-inhibiting antidepressants (e.g., paroxetine, fluoxetine) in patients treated with tamoxifen for breast cancer. Nevertheless, dispensing data for tamoxifen and seven regularly used SSRIs/SNRIs in the period between 2005 and 2010, obtained from a large community pharmacy database in the Netherlands (3,000,000 people), show that the potent CYP2D6-inhibiting drug paroxetine remains one of the most frequently used antidepressants in tamoxifen-treated patients. Moreover, trends in the use of SSRIs/SNRIs in the population of all women were similar with trends in women using tamoxifen. Apparently, the recommendations to avoid paroxetine in tamoxifen-treated women have not been implemented into clinical practice. Several reasons may underlie continued use of this drug-drug combination. Contrary to CYP2D6 polymorphisms, drug-induced CYP2D6 inhibition can easily be avoided, since alternative drugs are available. In clinical practice, one should strive to avoid potent CYP2D6 inhibitors as much as possible in tamoxifen-treated patients to reduce the risk of compromising the efficacy of the hormonal therapy. Co-medication should be reviewed by both physicians and pharmacists and potent CYP2D6 inhibitors ought to be switched to weaker alternatives.

Taking into account the high frequency of adverse drug reactions (ADRs) in the clinic and taking into account the growing knowledge of the genetic mechanisms underlying some of these ADRs, we believe that every clinician should know at least the basic principles of pharmacogenetics. However, our experience is that many clinicians are unaware of the potential contribution of pharmacogenetic testing and have not implemented this new modality in their daily practice. We present a case of Stevens-Johnson syndrome in a patient treated with carbamazepine. Following the pathways of clinical reasoning, we describe the possibilities of pharmacogenetic testing in the clinic (HLA-B*1502 and HLA-A*3101 in our patient). We describe the pharmacological and pharmacogenetic aspects relevant for the clinician's daily practice (the existence of ADR subtypes, cytochrome P450, drug-drug interactions, genetic variations, CYP450 and HLA genotyping). Based on the Dutch top 100 of most prescribed drugs, we provide data on CYP450 and HLA genotypes relevant to those 100 most commonly used drugs. We discuss the availability and costs of pharmacogenetic testing, show a calculation of the 'number needed to genotype' and, based on these data, we propose a decision model for pharmacogenetic testing by clinicians.

Objective: P450 oxidoreductase (POR) is essential for cytochrome P450 (CYP) activity in humans. The POR*28 allele (A503V) has been shown to impact on in-vitro CYP-mediated metabolism, including CYP3A isoenzymes. The aim of the present study was to determine the in vivo impact of the POR*28 allele on the pharmacokinetics of the classic CYP3A phenotyping probes midazolam and erythromycin. Whereas midazolam is metabolized by both CYP3A4 and CYP3A5, erythromycin is exclusively oxidized by CYP3A4., Materials and Methods: To assess CYP3A activity, 108 cancer patients received midazolam and 45 others underwent the erythromycin breath test. Patients were genotyped for POR*28, CYP3A4*22 and CYP3A5*3., Results: In patients expressing CYP3A5, POR*28 carriers showed 45% lower midazolam metabolic ratios compared with POR*1/*1 patients (P<0.001). This is in line with a lower CYP3A5 activity toward midazolam for POR*28 carriers. In CYP3A5 nonexpressers, POR*28 had no influence on midazolam pharmacokinetics. For erythromycin, POR*28 carriership did not influence its metabolism., Conclusion: Our data show that the POR*28 allele is associated with a lower in vivo CYP3A5 activity, but has no effects on CYP3A4-mediated erythromycin and midazolam metabolism.

Many studies have attempted to explain the interindividual variability observed in drug metabolism by assessing the impact of SNPs in genes implicated in drug absorption, distribution, metabolism and excretion pathways. Particular attention has been paid to the CYP450s. CYP3A4 is the main CYP isoform in human liver and intestine and is involved in the metabolism of many drugs. Its activity, however, is characterized by widespread variation in the general population, which is thought to have a genetic basis. A new CYP3A4 allele (CYP3A4*22; rs35599367 C>T in intron 6) with a frequency of 5-7% in the Caucasian population was recently discovered through its association with low hepatic CYP3A4 expression and CYP3A4 activity, and showing effects on statin, tacrolimus and cyclosporine metabolism. This review will summarize the current literature on phenotypes linked to this new promising CYP3A4 genetic marker SNP and discusses the potential clinical relevance.

Every month, new releases on the relationship between pharmacogenetic biomarkers and immunosuppressive drug therapy in kidney transplantation are published. However, the systematic clinical application of these discoveries occurs at a very slow pace, and the usefulness of knowing a patient's genotype remains an important matter of debate. This can be partially ascribed to the lack of consistency when looking at the different associations reported across several studies but also the need for a broad-spectrum view and a rigorous analysis of the relevance of the different associations observed to date. For that purpose, we performed a comprehensive analysis of the strength of the different reported genetic associations, and in this article we discuss their potential for clinical implementation in kidney transplantation. For tacrolimus, it is likely that a genotype-based drug dosage can benefit patient outcome, while for ciclosporin A, the data appear less convincing. For the mammalian target of rapamycin inhibitors, sirolimus and everolimus - given the lack of data and the absence of large prospective studies - it is premature to implement pharmacogenetics, but some novel and promising leads have recently been reported. For mycophenolate mofetil, the complex metabolic pathways of its active moiety, mycophenolic acid, complicate analysis of the various published associations. However, at present, some interesting findings can be highlighted and offer potential value to assist clinicians in decision making.

Immunosuppressive drugs used in organ transplantation are highly effective in preventing acute rejection. However, the clinical use of these drugs is complicated by the fact that they display highly variable pharmacokinetics and pharmacodynamics between individual patients. The influence of genetic variation on the interindividual variability in immunosuppressive drug disposition, efficacy, and toxicity has been explored in recent years. The polymorphically-expressed ATP-binding cassette (ABC) transporter proteins, in particular ABCB1 and ABCC2, have been investigated extensively because they play an important role in the absorption, distribution and elimination of many immunosuppressive drugs in use today. From these studies it can be concluded that polymorphisms in ABCB1 and ABCC2 have no consistent effect on immunosuppressant pharmacokinetics and toxicity although polymorphisms in ABCB1 appear to be related to the risk of developing calcineurin inhibitor-related nephrotoxicity. However, the latter needs to be replicated before an individual's ABCB1 genotype can become a useful marker that is applied in clinical practice. Future studies evaluating the influence of ABC transporter gene polymorphisms should explore the relationship with intracellular rather than systemic drug concentrations further in well-designed clinical studies. Until then, single-nucleotide polymorphisms in ABC transporter genes are not suitable to act as biomarkers for solid organ transplantation., (Copyright © 2011 Elsevier B.V. All rights reserved.)

High intra-patient variability in TCL exposure is a risk factor for allograft loss and late acute rejection. We hypothesized that a higher intra-patient variability leads to a faster decline in GFR in pediatric renal transplant patients and that adolescents have a higher intra-patient variability due to poorer adherence. We included 69 children aged 3.5-18 yr who had undergone renal transplantation between April 1996 and May 2009 in two pediatric nephrology centers in the Netherlands. We analyzed TCL trough concentrations over a period of one yr and calculated TCL trough concentrations variability using VC. We investigated the correlation between the TCL trough concentrations variability and the decline in estimated GFR over four yr. The median intra-patient variability in TCL concentrations was 30.1% (range 8.6-77.6) and the mean GFR slope -3.8 mL/min/1.73 m(2) /yr. The VC correlated neither with the GFR slope, nor with the patients' age. However, children with late acute rejection had higher VC (p = 0.045). We were unable to provide evidence that a high variability in TCL exposure leads to a faster decline in renal function, although children with late acute rejection have a higher variability in TCL exposure. Adolescents do not have a higher intra-patient variability in TCL trough concentrations than younger children., (© 2012 John Wiley & Sons A/S.)

Tamoxifen undergoes biotransformation into several metabolites, including endoxifen. Differences in metabolism contribute to the interindividual variability in endoxifen concentrations, potentially affecting treatment efficacy. We evaluated the effects of cytochrome P450 (CYP) induction by rifampicin on the exposure levels of tamoxifen and its metabolites and found that coadministration of rifampicin resulted in markedly reduced (up to 86%, P ≤ 0.040) concentrations of tamoxifen and its metabolites. Given the extensive metabolism undergone by tamoxifen, several factors may have contributed to this effect. Similar drug-drug interactions may exist between tamoxifen and other strong CYP inducers.

Objective: We investigated the association between genetic polymorphisms in ABCB1 and SLCO1B and mycophenolic acid (MPA) pharmacokinetics, and MPA-related diarrhea and leukopenia in 338 kidney transplant recipients., Methods: A total of 338 patients participating in an international, randomized-controlled clinical trial were genotyped for ABCB1 and SLCO1B. Patients were all treated with mycophenolate mofetil and either cyclosporine or tacrolimus. MPA-area under the curve (AUCs), MPA-glucuronide AUCs and acylglucuronide-AUCs were measured on days 3 and 10, and months 1, 3, 6, and 12 after kidney transplantation., Results: The risk of developing diarrhea was 1.8-fold higher in patients cotreated with tacrolimus compared with patients cotreated with cyclosporine (95% confidence interval: 1.03-3.13; P=0.038). ABCB1 and SLCO1B SNPs were not associated with dose-adjusted exposure to MPA, MPA-glucuronide, nor acylglucuronide-MPA nor with the incidence of diarrhea or leukopenia., Conclusion: Genotyping for ABCB1 or SLCO1B pretransplantation is unlikely to be of clinical value for individualization of MPA therapy.

Objective: Cyclosporine A (CsA) is a substrate of cytochrome P450 3A4 (CYP3A4). Recently, a newly discovered intron 6 single-nucleotide polymorphism in CYP3A4 (rs35599367 C>T), defining the CYP3A4*22 allele, has been linked to reduced hepatic expression and activity of CYP3A4. In the present study, the clinical impact of this single-nucleotide polymorphism was investigated in a cohort of patients receiving a CsA-based immunosuppressive regimen., Materials and Methods: A total of 172 de-novo kidney transplant recipients, receiving CsA/mycophenolate mofetil as immunosuppressive therapy and participating in the Fixed-Dose Concentration Controlled study, were genotyped for the new CYP3A4*22 allele. CsA C(0) and/or C(2) levels were measured on days 3 and 10 and in months 1, 3, 6, and 12 after transplantation. Plasma creatinine concentrations, delayed graft function (DGF), and biopsy-proven acute rejection were recorded., Results: The CYP3A4*22 allele was significantly associated with a higher risk of DGF compared with the CYP3A4*1/*1 patients after adjustment for known risk factors [odds ratio (OR)=6.34, confidence interval (CI(95%): 1.38-29.3), P=0.015]. Mixed-model analysis demonstrated that the overall creatinine clearance was 20% lower in CYP3A4*22 allele carriers compared with CYP3A4*1/*1 patients [CI(95%) (-33.1 to -7.2%), P=0.002]. For ABCB1 3435C>T, T-variant carriers had a decreased risk of developing DGF compared with CC patients [CT: OR=0.30, CI(95%) (0.11-0.77), P=0.011; TT: OR=0.18, CI(95%) (0.05-0.67), P=0.011]., Conclusion: CYP3A4*22 constitutes a risk factor for DGF and worse creatinine clearance in patients receiving CsA-based immunosuppressive therapy. Therefore, pretransplant genotyping for the CYP3A4*22 allele might help clinicians to identify patients at risk of DGF and poor renal function when treated with CsA.

In view of future pharmacokinetic studies, a highly sensitive ultra performance liquid chromatography/tandem mass spectrometry (UPLC-MS/MS) method has been developed for the simultaneous quantification of tamoxifen and three of its main phase I metabolites in human lithium heparinized plasma. The analytical method has been thoroughly validated in agreement with FDA recommendations. Plasma samples of 200 μl were purified by liquid-liquid extraction with 1 ml n-hexane/isopropanol, after deproteination through addition of 50 μl acetone and 50 μl deuterated internal standards in acetonitrile. Tamoxifen, N-desmethyl-tamoxifen, 4-hydroxy-tamoxifen and endoxifen were chromatographically separated on an Acquity UPLC(®) BEH C18 1.7 μm 2.1 mm×100 mm column eluted at a flow-rate of 0.300 ml/min on a gradient of 0.2mM ammonium formate and acetonitrile, both acidified with 0.1% formic acid. The overall run time of the method was 10 min, with elution times of 2.9, 3.0, 4.1 and 4.2 min for endoxifen, 4-hydroxy-tamoxifen, N-desmethyl-tamoxifen and tamoxifen, respectively. Tamoxifen and its metabolites were quantified by triple-quadrupole mass spectrometry in the positive ion electrospray ionization mode. The multiple reaction monitoring transitions were set at 372>72 (m/z) for tamoxifen, 358>58 (m/z) for N-desmethyl-tamoxifen, 388>72 (m/z) for 4-hydroxy-tamoxifen and 374>58 (m/z) for endoxifen. The analytical method was highly sensitive with the lower limit of quantification validated at 5.00 nM for tamoxifen and N-desmethyl-tamoxifen and 0.500 nM for 4-hydroxy-tamoxifen and endoxifen, which is equivalent to 1.86, 1.78, 0.194 and 0.187 ng/ml for tamoxifen, N-desmethyl-tamoxifen, 4-hydroxy-tamoxifen and endoxifen, respectively. The method was also precise and accurate, with within-run and between-run precisions within 12.0% and accuracy ranging from 89.5 to 105.3%. The method has been applied to samples from a clinical study and cross-validated with a validated LC-MS/MS method in serum., (Copyright © 2011 Elsevier B.V. All rights reserved.)