Nauras Shuker

A Randomized Controlled Trial Comparing the Efficacy of Cyp3a5 Genotype-Based With Body-Weight-Based Tacrolimus Dosing After Living Donor Kidney Transplantation.

Patients expressing the cytochrome P450 (CYP) 3A5 gene require a higher tacrolimus dose to achieve therapeutic exposure compared with nonexpressers. This randomized‐controlled study investigated whether adaptation of the tacrolimus starting dose according to CYP3A5 genotype increases the proportion of kidney transplant recipients being within the target tacrolimus predose concentration range (10–15 ng/mL) at first steady‐state. Two hundred forty living‐donor, renal transplant recipients were assigned to either receive a standard, body‐weight‐based or a CYP3A5 genotype‐based tacrolimus starting dose. At day 3, no difference in the proportion of patients having a tacrolimus exposure within the target range was observed between the standard‐dose and genotype‐based groups: 37.4% versus 35.6%, respectively; p = 0.79. The proportion of patients with a subtherapeutic (i.e. <10 ng/mL) or a supratherapeutic (i.e. >15 ng/mL) Tac predose concentration in the two groups was also not significantly different. The incidence of acute rejection was comparable between both groups (p = 0.82). Pharmacogenetic adaptation of the tacrolimus starting dose does not increase the number of patients having therapeutic tacrolimus exposure early after transplantation and does not lead to improved clinical outcome in a low immunological risk population.

Intra-patient variability in tacrolimus exposure: causes, consequences for clinical management.

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.

Clinical implementation of pharmacogenetics in kidney transplantation: Calcineurin inhibitors in the starting blocks

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.

ATP-binding cassette transporters as pharmacogenetic biomarkers for kidney transplantation.

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 individuals 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.

A high intrapatient variability in tacrolimus exposure is associated with poor long-term outcome of kidney transplantation.

Tacrolimus is a critical dose drug with a considerable intrapatient variability (IPV) in its pharmacokinetics. We investigated whether a high IPV in tacrolimus exposure is associated with adverse long-term renal transplantation outcomes. Tacrolimus IPV was calculated from predose concentrations measured between 6 and 12 months post-transplantation of 808 renal transplant recipients (RTRs) transplanted between 2000 and 2010. One hundred and eighty-eight (23.3%) patients reached the composite end point consisting of graft loss, late biopsy-proven rejection, transplant glomerulopathy, or doubling of serum creatinine concentration between month 12 and the last follow-up. The cumulative incidence of the composite end point was significantly higher in patients with high IPV than in patients with low IPV (hazard ratio: 1.41, 95% CI: 1.06-1.89; P = 0.019). After the adjustment for several factors, the higher incidence of the composite end point for RTRs with a high IPV remained statistically significant (hazard ratio: 1.42, 95% CI: 1.06-1.90; P = 0.019). Younger recipient age at transplantation, previous transplantation, worse graft function (at month 6 post-transplantation), and low mean tacrolimus concentration at 1 year post-transplantation were additional predictors for worse long-term transplant outcome. A high tacrolimus IPV is an independent risk factor for adverse kidney transplant outcomes that can be used as an easy monitoring tool to help identify high-risk RTRs.

Conversion from twice-daily to once-daily tacrolimus does not reduce intrapatient variability in tacrolimus exposure

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.

Conversion to Once-daily Tacrolimus Results in increased p38MAPK Phosphorylation in T-lymphocytes of Kidney Transplant Recipients

Background: The once-daily formulation of tacrolimus (TACOD) has been developed to overcome adherence problems. Conversion from the twice-daily TAC (TACBID) formulation to TACOD on a 1:1 basis, however, often leads to a decrease of TAC predose concentrations, which averages ∼15%. Switching between the two TAC formulations may thus influence drug efficacy and necessitates therapeutic drug monitoring. As an additional tool in transplantation diagnostics, phospho-specific flow cytometry was used to study the biological effects of conversion on p38MAPK phosphorylation, a kinase involved in T-lymphocyte activation. Methods: Stable renal transplant recipients (n = 12), at least 1 year after their transplantation, were converted from TACBID to TACOD on 1:1 mg for mg base. Comedication consisted of mycophenolate mofetil (n = 10) and prednisolone (n = 3). TAC whole-blood predose concentrations were determined by immunoassay before and 3 months after conversion. P38MAPK phosphorylation was measured in T lymphocytes by whole-blood phospho-specific flow cytometry. Results: Three months after conversion, no significant decreases in TAC predose concentrations (C0) were found (P = 0.54), whereas p38MAPK phosphorylation increased with 11.4% (P < 0.05) in CD4+ and with 15.6% (P < 0.05) in CD8+ T lymphocytes. The TAC C0 during treatment with TACBID correlated inversely with p38MAPK phosphorylation in T lymphocytes (rs = −0.638; P < 0.05). Conclusions: These results suggest that the measurement of p38MAPK phosphorylation status in T lymphocytes is a sensitive method to determine the biological effects of TAC before and after conversion from TACBID to TACOD. This method could be a more sensitive tool for therapeutic drug monitoring of TAC.

Mycophenolic acid-related anemia and leucopenia in renal transplant recipients are related to genetic polymorphisms in CYP2C8.

W ith great interest we read the article by Jacobson et al. (1) who observed that single-nucleotide polymorphisms (SNPs) in IL12A (rs568408G9A), CYP2C8 (rs11572076G9A), and HUS1 (rs1056663C9T) are associated with the occurrence of mycophenolic acid (MPA)related anemia but not leucopenia. These SNPs were identified by studying 978 renal transplant recipients by use of customized, commercially available gene chips that included a total of 2724 polymorphisms. Although the exact pathophysiological mechanism of these genotype-phenotype associations is not known, IL-12 mRNA levels were previously shown to be elevated in patients with aplastic anemia, HUS1 seems to be involved in the cellular response to DNA damage, and CYP2C8 may produce the 6-Odesmethyl-MPA metabolite. However, the data of Jacobson et al. were not confirmed in an independent cohort. The aim of our study was to investigate whether these SNPs are indeed associated with the occurrence of MPA-related anemia and leucopenia after kidney transplantation. The patients described herein were de novo kidney transplant recipients who participated in a trial comparing fixeddose (FD) mycophenolate mofetil (MMF) treatment with concentration-controlled (CC) MMF treatment. The primary outcomes of this so-called fixed-dose concentration-controlled (FDCC) trial were reported previously (2). Immunosup pressive therapy consisted of MMF combined with cyclosporine or tacrolimus, and prednisolone according to local practice. Anemia was defined as a hemoglobin level G11.3 g/dL (7.0 mmol/L) occurring after day 28 posttransplantation. Leucopenia was defined as a total leukocyte count G3.0 10/L. Of the total of 901 patients participating in the FDCC trial, 338 agreed to participate in a pharmacogenetic substudy. Genomic DNA was isolated from 200 KL EDTA whole blood using a MagnaPure LC (Roche Diagnostics GmbH, Mannheim, Germany). Allelic discrimination reactions were realized using TaqMan (Applied Biosystems, CA) genotyping assays (C___2423981_10, C___1825446_20 and C__31658115_10) for rs568408G9A in IL12A, rs1056663C9T in HUS1, and rs11572076G9A in CYP2C8 on a ABI PRISM 7500 Fast Real-Time PCR System (Applied Biosystems) using 20 ng genomic DNA according to the manufacturer’s instructions. For this analysis, data on the incidence of anemia and leucopenia of 332 of the 338 patients MMF (n=178) were analyzed separately from those who received CC MMF (n=154). Only in the CC group was the MMF dose adjusted on the basis of repetitive pharmacokinetic sampling results (3). The allele frequencies of the various SNPs were as follows: CYP2C8 G 99.5%, CYP2C8 A 0.5%, IL12A A 15.1% and IL12A G 84.9%, and HUS1 C 51.1% and HUS1 T 48.9%. They were all in Hardy-Weinberg equilibrium. When we studied the allele frequencies in the FD and the CC group separately, comparable allele frequencies were observed, with the exception of the distribution of the CYP2C8 SNP in the CC group: in this group, all patients had the GG genotype. Anemia occurred in 65 patients (37%) in the FD group and in 61 patients (40%) in the CC group, which was not significantly different (P=0.56). No significant differences in the frequency of the investigated IL12A and HUS1 SNPs were found between patients with and those without anemia in the FD and CC groups (Table 1). For the CYP2C8 SNP, a significant association (P=0.021) was observed in the FD group with 100% of patients with the CYP2C8 rs11572076GA genotype having anemia (Table 1). However, only three patients (2%) had the GA genotype, yielding low statistical power. In fact, based on the reported (1) increased relative risk (1.75) of developing anemia in association with the CYP2C8 A variant allele, a sample size of 2300 patients (23 patients with anemia and 2277 control subjects) would have been necessary to have an 80% power with an alpha of 0.05% to reject the null hypothesis. However, this being a substudy of the completed FDCC trial, we think that one should be cautious about performing such post hoc sample size calculations (4Y6). The incidence of leucopenia was comparable in the FD and CC groups: 24 patients (14%) vs. 32 patients (21%), respectively (P=0.10). No significant associations were observed between the different IL12A and HUS1 SNPs and the incidence of leucopenia, both in the CC and the FD groups (Table 1). However, a significant association between the CYP2C8 rs11572076G9A SNP and leucopenia was observed in the FD group with patients carrying the variant allele having a higher risk of developing this adverse event: 67% (n=2) vs. 13% (n=22), respectively (P=0.007; Table 1). Our results support the observation made by Jacobson et al. (1) that CYP2C8 rs11572076A allele carriers have a higher risk to develop anemia. However, the actual number of patients carrying this variant allele was small and thereforeVdespite the fact that this association was confirmatoryVthe possibility of a spurious finding remains. The association of the CYP2C8 rs11572076A allele with anemia was observed in the FD MMF group. In contrast to patients who received a CC MMF dose (where any effects of genetic variation may be obscured by therapeutic drug monitoring), no dose adjustment based on plasma MPA concentrations was made in the FD group, allowing for the full CORRESPONDENCE

Overweight Kidney Transplant Recipients Are at Risk of Being Overdosed Following Standard Bodyweight-Based Tacrolimus Starting Dose

Background Bodyweight-based dosing of tacrolimus (Tac) is considered standard care, even though the available evidence is thin. An increasing proportion of transplant recipients is overweight, prompting the question if the starting dose should always be based on bodyweight. Methods For this analysis, data were used from a randomized-controlled trial in which patients received either a standard Tac starting dose or a dose that was based on CYP3A5 genotype. The hypothesis was that overweight patients would have Tac overexposure following standard bodyweight-based dosing. Results Data were available for 203 kidney transplant recipients, with a median body mass index (BMI) of 25.6 (range, 17.2-42.2). More than 50% of the overweight or obese patients had a Tac predose concentration above the target range. The CYP3A5 nonexpressers tended to be above target when they weighed more than 67.5 kg or had a BMI of 24.5 or higher. Dosing guidelines were proposed with a decrease up to 40% in Tac starting doses for different BMI groups. The dosing guideline for patients with an unknown genotype was validated using the fixed-dose versus concentration controlled data set. Conclusions This study demonstrates that dosing Tac solely on bodyweight results in overexposure in more than half of overweight or obese patients.

Intrapatient Variability in Tacrolimus Exposure Does Not Predict The Development of Cardiac Allograft Vasculopathy After Heart Transplant

OBJECTIVE A high intrapatient variability in tacrolimus exposure is associated with poor long-term outcomes after kidney transplant. We hypothesized that a high intrapatient variability of tacrolimus exposure after heart transplant may be associated with cardiac allograft vasculopathy as a determinant of long-term survival of heart transplant recipients. MATERIALS AND METHODS Eighty-six heart transplant recipients were included. Patients underwent coronary angiography at years 1 and 4 after transplant and were divided according to low and high intrapatient variability of tacrolimus exposure, with the median variability as cut-off. The primary outcome was the association between tacrolimus intrapatient variability and the progression of cardiac allograft vasculopathy score between years 1 and 4. Secondary outcome was this association with acute cellular rejection. RESULTS There was no significant difference in the proportion of patients with high tacrolimus intrapatient variability in the group that progressed to higher grades of cardiac allograft vasculopathy (n = 15) versus the group without progression (n = 71) at 4-year follow-up (60.0% vs 47.9%; P = .57). There was no significant difference in the proportion of patients with high tacrolimus intrapatient variability between the 58 patients with 1 or more acute cellular rejection episodes and the 28 patients without rejection (51.7% vs 46.4%; P = .82). CONCLUSIONS A high intrapatient variability in tacrolimus exposure does not appear to influence heart transplant outcomes, unlike its influence on kidney transplant function. A higher immunosuppression exposure after heart transplant, including the use of prednisone often in a combination of 3 immunosuppressive drugs, may protect against the effects of high intrapatient tacrolimus variability.