Tacrolimus Dose Requirements Research Articles

Which Genetic Determinants Should be Considered for Tacrolimus Dose Optimization in Kidney Transplantation? A Combined Analysis of Genes Affecting the CYP3A Locus.

Tacrolimus is established as immunosuppressant after kidney transplantation. Polymorphism of the cytochrome P450 3A5 (CYP3A5) gene contributes significantly to tacrolimus dose requirements. Recently, CYP3A4*22 was reported to additionally affect tacrolimus pharmacokinetics (PK). In addition, there are further polymorphic genes, possibly influencing CYP3A activity [pregnane x receptor NR1I2, P450 oxidoreductase (POR), and peroxisome proliferator-activator receptor alpha (PPARA)]. We aimed to investigate combined effects of these gene variants on tacrolimus maintenance dose and PK in patients with stable kidney transplantation of 2 study centers. A total of 223 white patients (German cohort, 136; Danish cohort, 87) was included and genotyped for CYP3A5 (rs776746), CYP3A4 (rs35599367), NR1I2 (rs2276707), POR (rs1057868), and PPARA (rs4253728). Dosage and trough concentration/dose ratios were considered separately. A subset was investigated for comprehensive PK parameters. Tacrolimus dose, trough concentration, and trough concentration/dose ratio did not differ between the German and Danish cohort. CYP3A5*3 and CYP3A4*22 contributed to dose requirements only in the German and in the total cohort. Homozygous carriers of both variants required 4.8 ± 3.1 mg, whereas carriers of the wild types required 165% higher mean tacrolimus doses (12.5 ± 7.7 mg, P = 1.4 × 10). The PK investigation revealed only nonsignificant impact of CYP3A4 genotypes on AUC12h in CYP3A5 nonexpressers (P = 0.079, power = 57%). For the entire sample, the final multiple linear regression model for trough concentration/dose ratio included CYP3A5, CYP3A4, and age. It explained 18.3% of the interindividual variability of tacrolimus trough concentration/dose ratios (P = 8.8 × 10). Therapeutic drug monitoring remains essential in clinical care of patients with kidney transplantation. Genotyping of CYP3A5 and CYP3A4, however, could facilitate rapid dose finding to adapt the appropriate immunosuppressant dose, whereas other genetic factors had only little or no effect.

Influence of CYP3A5 genotypes on tacrolimus dose requirement: age and its pharmacological interaction with ABCB1 genetics in the Chinese paediatric liver transplantation.

The purpose of the study was to evaluate the impact of single nucleotide polymorphisms (SNPs) of Cytochrome P450 (CYP) 3A5 and adenosine triphosphate-binding cassette B1 (ABCB1) genotypes on TAC pharmacokinetics in Chinese paediatric patients. A total of 136 Chinese paediatric liver recipients (R) and their donors (D) were divided into groups according to their CYP3A5 genotypes [expression of *1 allele: expressor (EX) or non-expressor (NEX)]. Both recipient and donor CYP3A5*1 alleles had impacts on the TAC pharmacokinetics after liver transplantation. EX-R/EX-D recipients required a significantly higher TAC daily dose compared with NEX-R/NEX-D (0.24 ± 0.08 vs. 0.14 ± 0.06 mg/kg/day, p < 0.01). Age was also an independent factor on TAC requirement. Compared with EX-R/EX-D, non-expressor infants or recipients over 3-years old needed < 0.2 mg/kg/day. None of the ABCB1 SNPs (1236C>T, 2677G>A/T, 3435C>T) had an impact on TAC pharmacokinetics. However, EX-R/EX-D recipients bearing the ABCB1 1236-CC genotype required a much higher TAC dose than those without this genotype (0.23 vs. 0.18 mg/kg/day, p < 0.01), who required a similar TAC dose to that of NEX-R/NEX-D children. Furthermore, EX-R/EX-D with ABCB1 1236-CC recipients exhibited an markedly higher incidence of acute rejection and transplant-related infections clinically. CYP3A5 and ABCB1-1236 genotyping, in addition to recipient age, are necessary for establishing a more accurate TAC dosage regimen in paediatric liver recipients. We should be cautious regarding the treatment of paediatric recipients with both CYP3A5-expressor and ABCB1 1236-CC genotypes with TAC, as these patients are more susceptible to acute rejection and infection.

Gut microbiota and tacrolimus dosing in kidney transplantation.

Tacrolimus dosing to establish therapeutic levels in recipients of organ transplants is a challenging task because of much interpatient and intrapatient variability in drug absorption, metabolism, and disposition. In view of the reported impact of gut microbial species on drug metabolism, we investigated the relationship between the gut microbiota and tacrolimus dosing requirements in this pilot study of adult kidney transplant recipients. Serial fecal specimens were collected during the first month of transplantation from 19 kidney transplant recipients who either required a 50% increase from initial tacrolimus dosing during the first month of transplantation (Dose Escalation Group, n=5) or did not require such an increase (Dose Stable Group, n=14). We characterized bacterial composition in the fecal specimens by deep sequencing of the PCR amplified 16S rRNA V4-V5 region and we investigated the hypothesis that gut microbial composition is associated with tacrolimus dosing requirements. Initial tacrolimus dosing was similar in the Dose Escalation Group and in the Stable Group (4.2±1.1 mg/day vs. 3.8±0.8 mg/day, respectively, P=0.61, two-way between-group ANOVA using contrasts) but became higher in the Dose Escalation Group than in the Dose Stable Group by the end of the first transplantation month (9.6±2.4 mg/day vs. 3.3±1.5 mg/day, respectively, P<0.001). Our systematic characterization of the gut microbial composition identified that fecal Faecalibacterium prausnitzii abundance in the first week of transplantation was 11.8% in the Dose Escalation Group and 0.8% in the Dose Stable Group (P=0.002, Wilcoxon Rank Sum test, P<0.05 after Benjamini-Hochberg correction for multiple hypotheses). Fecal Faecalibacterium prausnitzii abundance in the first week of transplantation was positively correlated with future tacrolimus dosing at 1 month (R=0.57, P=0.01) and had a coefficient±standard error of 1.0±0.6 (P=0.08) after multivariable linear regression. Our novel observations may help further explain inter-individual differences in tacrolimus dosing to achieve therapeutic levels.

ABCB1 (MDR-1) pharmacogenetics of tacrolimus in renal transplanted patients: a Next Generation Sequencing approach.

A CYP3A5 gene polymorphism is the main determinant of Tacrolimus (Tac) dose requirements among renal transplanted patients. In spite of the utility of CYP3A5 genotyping to predict the Tac-dose, many patients exhibit an out of range blood Tac level and it is thus likely that other genes/polymorphisms contribute to define Tac bioavailability. To address this issue we searched for coding sequence variants in the ABCB1/MDR1 gene in renal transplanted patients treated with Tac and who had out of the range blood levels. We studied 100 renal transplanted patients treated with Tac, 60 of whom had Tac blood levels below (n=39) and above (n=21) the target range (10-15 ng/mL) at 1 week post-transplant. The DNA was subjected to multiplex amplification followed by massive parallel semiconductor sequencing in the Ion Torrent personal genome machine. We found four missense changes, all reported and present in cases above and below the blood Tac target. In addition, we did not find differences in the allele and genotype frequencies for the common rs1045642 polymorphism (p.I1145I) between the groups. Our results suggested that the ABCB1 variants had no effect on the risk of showing out of range Tac blood levels among renal transplanted patients.

Combined effects of CYP3A5*1, POR*28, and CYP3A4*22 single nucleotide polymorphisms on early concentration-controlled tacrolimus exposure in de-novo renal recipients.

In a cohort of 298 de-novo renal recipients treated with a standard tacrolimus loading dose of 0.2 mg/kg, the combined effects of the CYP3A5*1, POR*28, and CYP3A4*22 genotypes on early tacrolimus exposure (C0), dose requirements, and achievement of the therapeutic target, C0, were examined. The incidence of clinical events (e.g. acute rejection, diabetes mellitus) was compared between genotypes. Fast metabolizers (CYP3A5*1/POR*28T carriers) had two-fold to three-fold higher tacrolimus dose requirements compared with slow metabolizers (CYP3A5*3/*3/CYP3A4*22 carriers) and needed significantly more time to achieve the target tacrolimus C0 of a minimum 10 ng/ml (3.3±1.7 vs. 1.34±0.75 days; P<0.0001). No differences in acute rejection incidence and time to first rejection were observed. Slow metabolizers more frequently had tacrolimus C0 above the target range early after transplantation (70 vs. 13% on day 3); however, this did not translate into a higher incidence of post-transplantation diabetes mellitus or graft dysfunction. Multivariate analyses identified the CYP3A5*1/POR*28/CYP3A4*22 genotype combination as the single strongest determinant of tacrolimus dose requirements throughout the first year, explaining between 24-40% of its variability, whereas recipient age, hematocrit, and delayed graft function were additional nongenetic determinants of tacrolimus dose. Combining the CYP3A5*1, POR*28 and CYP3A4*22 genotypes allows partial differentiation of early tacrolimus dose requirements and the time to reach therapeutic target concentrations after transplantation, but without obvious clinical implications. Larger prospective studies need to address the clinical relevance of early combined genotype-based tacrolimus dosing in de-novo renal recipients.

Personalized tacrolimus dose requirement by CYP3A5 but not ABCB1 or ACE genotyping in both recipient and donor after pediatric liver transplantation.

Tacrolimus (TAC) is the backbone of an immunosuppressive drug used in most solid organ transplant recipients. A single nucleotide polymorphism (SNP) at position 6986G>A in CYP3A5 has been notably involved in the pharmacokinetic variability of TAC. It is hypothesized that CYP3A5 genotyping in patients may provide a guideline for TAC therapeutic regimen. To further evaluate the impact of CYP3A5 variants in donors and recipients, ABCB1 and ACE SNPs in recipients on TAC disposition, clinical and laboratory data were retrospectively reviewed from 90 pediatric patients with liver transplantation and their corresponding donors after 1 year of transplantation. The recipients with CYP3A5 *1/*1 or *1/*3 required more time to achieve TAC therapeutic range during the induction phase, and needed more upward dose during the late induction and the maintained phases, with lower C/D ratio, compared with those with CYP3A5 *3/*3. And donor CYP3A5 genotypes were found to impact on TAC trough concentrations after liver transplantation. No association between ABCB1 or ACE genotypes and TAC disposition post-transplantation was found. These results strongly suggest that CYP3A5 genotyping both in recipient and donor, not ABCB1 or ACE is necessary for establishing a personalized TAC dosage regimen in pediatric liver transplant patients.

Tacrolimus dosage requirements in lung transplant recipients receiving antifungal prophylaxis with voriconazole followed by itraconazole: a preliminary prospective study.

Concomitant administration of the triazole antifungals, voriconazole or itraconazole, with tacrolimus can result in significant drug interaction in the transplant recipient. Limited published information exists regarding tacrolimus dosing when transitioning from voriconazole to itraconazole. The objective of this study was to evaluate the extent of the drug interaction with antifungal prophylaxis using voriconazole followed by a change to itraconazole in lung transplant recipients receiving tacrolimus. This prospective study included lung transplant recipients receiving antifungal prophylaxis with voriconazole followed by a switch to itraconazole. Patients were followed from the time of transplant until two months after converting to itraconazole. All patients received standard immunosuppression with tacrolimus, mycophenolate mofetil, and a corticosteroid. Tacrolimus dose normalized concentrations using concentration/dose ratio were compared while receiving voriconazole versus itraconazole. Twenty lung transplant recipients were included in the final analysis. No difference was found with the tacrolimus dose normalized concentrations on voriconazole 254 ± 28 (ng/mL)/(mg/kg) compared with itraconazole 234 ± 34 (ng/mL)/(mg/kg), p = 0.65. Tacrolimus dosage adjustments were not necessary when converting from voriconazole to itraconazole. Validation in a larger population is needed to confirm these findings.

Tacrolimus Dose Requirements in African-American and Caucasian Kidney Transplant Recipients On Mycophenolate and Prednisone.

Tacrolimus Dose Requirements in African-American and Caucasian Kidney Transplant Recipients On Mycophenolate and Prednisone.

Clinical and Genetic Determinants of Tacrolimus Dose During Induction and Stable Phase of Therapy.

Background Tacrolimus is a calcineurin inhibitor widely used in patients undergoing solid organ transplantation. However, tacrolimus therapy is hindered by highly variable dose requirements in patients associated with toxicity and efficacy (prevention of rejection). Metabolism of tacrolimus via the cytochrome P450 (CYP) 3A family accounts for a significant portion of tacrolimus dosing requirements. Currently, there is paucity of data regarding predictors of tacrolimus dosing, particularly during the initiation (induction) phase of therapy. Thus, we assessed the differential impact of CYP3A genetic polymorphisms on tacrolimus dose and plasma exposure during induction and maintenance phases of therapy. Methods We enrolled 167 renal transplant patients treated with tacrolimus (as bid Prograf) who were at least 3 months post-transplant. Tacrolimus trough concentrations and dose adjustments during induction (0 - 3 months) and stable phase (after 3 months) were retrospectively analyzed. Results The mean tacrolimus dose required during both induction and stable phase was significantly greater in CYP3A5 expressors (CYP3A5*1/*1 and *1/*3) compared to non-expressors (CYP3A5*3/*3; P<0.0001). Importantly, dose-normalized trough concentrations were significantly lower for CYP3A5 expressors (P<0.0001). In addition, dose-normalized concentrations appeared to be consistent throughout the treatment periods, indicating that intrinsic metabolism of tacrolimus does not vary between induction and stable phase of therapy. Regression analysis indicated that CYP3A5*3 and CYP3A4*22 genotype, hemoglobin, and weight were significant predictors of induction dose, accounting for 30% of the variation, while CYP3A5*3 genotype, months post transplant, and age were significant predictors of stable dose, accounting for 42% of the variation. Other significant variables with less impact on tacrolimus dose include POR*28, ABCB1 3435C>T, PXR -25385C>T, and creatinine clearance. Conclusions We demonstrated that CYP3A5*3 genotype is the major determinant of tacrolimus dose variability during induction and stable therapy. Genetic variation in CYP3A4 (*22) was identified as yet unrecognized significant contributor to tacrolimus dose. These findings have the potential to individualize tacrolimus dosing, reduce time to target concentration, improve efficacy, and minimize toxicities. DISCLOSURES:Muirhead, N.: Grant/Research Support, Astella. Kim, R.: Grant/Research Support, Astella.

Conversion From Twice-Daily to Once-Daily Tacrolimus in Simultaneous Pancreas-Kidney Transplant Patients

BackgroundData on the effectiveness of once-daily tacrolimus (Tac-QD) in simultaneous pancreas-kidney (SPK) transplant patients are limited, which is of particular concern because diabetic gastroparesis may affect absorption. The aim of this study was to evaluate the clinical impact of converting SPK patients from twice-daily (Tac-BD) to Tac-QD. MethodsFrom November 2008 to August 2011, 27 SPK recipients (out of 130) were converted from Tac-BD to Tac-QD. Demographics, prescribed doses, trough levels, and creatinine, glucose, and HbA1c values were collected prospectively at the time of conversion and at 1, 2, 3, 6, and 12 months after conversion. ResultsThe mean time from transplantation to conversion was 35.81 ± 27.31 months, with 20 patients (74.07%) converted to Tac-QD >12 months after transplantation. There were no significant differences in the tacrolimus dose and trough levels before and after conversion and at all points during the follow-up. Creatinine, glucos,e and HbA1c levels remained stable throughout. Eight patients (29.63%) with gastroparesis had clinical outcomes, drug doses, and trough levels similar to all other patients. ConclusionsStable SPK recipients can safely be converted from Tac-BD to Tac-QD, with no clinical impact on the transplant function. Gastroparesis does not appear to influence tacrolimus dose requirements or trough levels.

Tacrolimus dose requirements in African-American and Caucasian kidney transplant recipients on mycophenolate and prednisone.

Racial differences among kidney transplant recipients may impact the total daily tacrolimus dose required to achieve therapeutic tacrolimus concentrations. Previous studies suggest that African Americans require higher doses to achieve similar therapeutic drug concentrations compared with Caucasians. Data were collected on a total of 147 de novo kidney transplant recipients. Tacrolimus total daily dose (TDD) requirements (mg/kg/d) and tacrolimus concentrations were retrospectively reviewed at discharge and at days 30, 60, and 90 after transplant. TDD requirements in African-American and Caucasian patients were 0.14mg/kg/d and 0.11mg/kg/d, respectively (p=0.005), at day 30. TDD requirements at day of hospital discharge and days 60 and 90 following transplant were significantly higher in African-American patients vs. Caucasian patients, with similar tacrolimus concentrations at all time points. This study suggests that when compared to Caucasians, African Americans require significantly higher TDD of tacrolimus to achieve similar tacrolimus concentrations. These findings provide transplant clinicians with a sense of certainty to more rapidly titrate daily tacrolimus doses in African-American patients to achieve therapeutic concentrations.

(301) - Effect of CYP3A4*22 and CYP3A5 Combined Genotypes on Tacrolimus Disposition in Heart Transplantation

The CYP3A4*22 and CYP3A5*3 polymorphisms have been associated with decreased tacrolimus (TAC) metabolism and decreased TAC dose requirements in numerous transplant (Tx) populations. The objective of this study was to determine the combined impact of CYP3A4*22 and CYP3A5*3 genotypes on TAC disposition in heart transplant (HTx) recipients.

African American Renal Transplant Recipients (RTR) Require Higher Tacrolimus Doses to Achieve Target Levels Compared to White RTR: Does Clotrimazole Help?

The number of African Americans (AAs) on the kidney waiting list is increasing in the United States. Several studies showed that AAs are at higher risk for rejection and graft loss. Because of genetic polymorphisms, AAs may metabolize calcineurin inhibitors faster than Caucasian (C) individuals. The goal of this study is to evaluate the tacrolimus (TAC) dose required to reach therapeutic levels and to assess the impact of clotrimazole on TAC metabolism in AAs compared to C patients. One hundred forty-two AA renal transplant recipients (RTRs) were compared to 309 C RTRs. Demographics were similar in both groups. Induction therapy and maintenance immunosuppression were similar in both groups and included TAC, mycophenolate acid (MPA), and steroids. The goal in all RTRs was to maintain a 12-hour trough level of 10 to 15 ng/mL in the first 3 months, 8 to 10 ng/mL for the first year, and 5 to 8 ng/mL thereafter. To achieve these levels, AA RTRs require a significantly higher dosage of TAC compared to C patients (5.9 ± 2.9 vs 3.6 ± 2 mg/d, respectively, P < .0001). By multivariate analysis, TAC dose requirements were not affected by age, gender, MPA or prednisone dose, diabetes, and renal function. Adding clotrimazole (CTM) to the RTR regimen significantly reduced the TAC dose requirements in all RTRs. When CTM was used, the TAC dose requirement was not statistically significantly different between AA and C patients (2.6 ± 1.2 mg/d vs 1.8 ± 1.5 mg/d, P = .07). We conclude that AAs required a higher TAC dose to reach the desired trough level in RTRs compared to C RTRs. The use of CTM eliminates the need for higher doses of TAC in AA RTRs. Thus, CTM may aid AA RTRs in achieving therapeutic TAC levels while reducing drug costs.

The Role of Pharmacogenetics in the Disposition of and Response to Tacrolimus in Solid Organ Transplantation

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 Anucleotide, defined as the *1 allele) have a dose requirement that is around 50% higher than non-expressers (those homozygous for the Gnucleotide, 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.

Meta-analysis and systematic review of the effect of the donor and recipient CYP3A5 6986A&gt;G genotype on tacrolimus dose requirements in liver transplantation

A meta-analysis was carried out of published studies on the effect of the CYP3A5 6986A>G polymorphism in liver donors and transplant recipients on tacrolimus pharmacokinetics. Cohort studies that evaluated the relationship between the CYP3A5 polymorphism in liver donors and transplant recipients and tacrolimus, trough blood concentration normalized for the daily dose (C) per kilogram body weight (D) (C/D, ng/ml/mg/kg/day) up to 1 year after transplantation, were included. Data were not restricted by patient age or the language or journal of publication. A literature search was conducted using the Cochrane Library, MEDLINE, EMBASE, and grey literature, and articles published up to 24 April 2013 were selected. Data were pooled (random-effects model), and the results were expressed as the mean difference of the corresponding C/D ratios and 95% confidence intervals. Six studies involving donor genotypes (254 patients) and four involving recipient genotypes (180 patients) were ultimately included. The meta-analysis showed the C/D ratio to be significantly higher in recipients with nonexpresser donor variants at all time points. In recipients, the variant did not influence the C/D ratio. The presence of the CYP3A5 6986A>G polymorphism in the donor affects tacrolimus pharmacokinetics in the recipient, although only the evidence available for the first month after transplantation was of adequate quality for demonstrating a significant difference. The evidence provided here shows no effect of the recipient genotype; however, the quality of the evidence was low, thereby precluding the drawing of firm conclusions.

Impact of donor and recipient CYP3A5 and ABCB1 genetic polymorphisms on tacrolimus dosage requirements and rejection in Caucasian Spanish liver transplant patients

Studies of liver transplant (LT) patients, mainly in Asians, have evaluated the influence of the CYP3A5*1 allele and P-glycoprotein gene ABCB1 on tacrolimus pharmacokinetics or biopsy-proven acute rejection (BPAR) incidence, with no conclusive results. To investigate these issues, 98 Caucasian Spanish LT patients with tacrolimus, mycophenolate mofetil and steroids and 88 cadaveric donors were genotyped for the SNPs CYP3A5 6986G>A, ABCB1 1236C>T, ABCB1 2677G>A/T and ABCB1 3435C>T;. On day 7 post-LT, patients with a native CYP3A5*1 allele had significantly lower tacrolimus trough concentrations C0 (P = .03) and dose-adjusted concentrations C0 /D (P = .02) than CYP3A5 *3/*3 homozygotes. Three months post-LT, patients carrying a liver with CYP3A5*1 had significantly lower C0 /D (P = .03) and took significantly higher tacrolimus doses (P = .03) than the corresponding *3/*3 homozygotes. ABCB1 SNPs showed no significant association with tacrolimus variables. The 3-month incidence of BPAR was 10.2%, with no statistically significant differences related to CYP3A5 (14.3% in expresser vs. 9.5% in non-expresser) or ABCB1 genotype of either patient or donor. We conclude that in Caucasian Spanish LT patients, a native or graft-borne CYP3A5*1 allele tends to lower tacrolimus concentrations and increase dosage needs, but has no significant impact on the incidence of BPAR.

A Markov Chain Model to Evaluate the Effect of CYP3A5 and ABCB1 Polymorphisms on Adverse Events Associated with Tacrolimus in Pediatric Renal Transplantation

The SNP A6986G of the CYP3A5 gene (*3) results in a non-functional protein due to a splicing defect whereas the C3435T was associated with variable expression of the ABCB1 gene, due to protein instability. Part of the large interindividual variability in tacrolimus efficacy and toxicity can be accounted for by these genetic factors. Seventy-two individuals were examined for A6986G and C3435T polymorphism using a PCR-RFLP-based technique to estimate genotype and allele frequencies in the Jordanian population. The association of age, hematocrit, platelet count, CYP3A5, and ABCB1 polymorphisms with tacrolimus dose- and body-weight-normalized levels in the subset of 38 pediatric renal transplant patients was evaluated. A Markov model was used to evaluate the time-dependent probability of an adverse event occurrence by CYP3A5 phenotypes and ABCB1 genotypes. The time-dependent probability of adverse event was about double in CYP3A5 non-expressors compared to the expressors for the first 12 months of therapy. The CYP3A5 non-expressors had higher corresponding normalized tacrolimus levels compared to the expressors in the first 3 months. The correlation trend between probability of adverse events and normalized tacrolimus concentrations for the two CYP3A5 phenotypes persisted for the first 9 months of therapy. The differences among ABCB1 genotypes in terms of adverse events and normalized tacrolimus levels were only observed in the first 3 months of therapy. The information on CYP3A5 genotypes and tacrolimus dose requirement is important in designing effective programs toward management of tacrolimus side effects particularly for the initial dose when tacrolimus blood levels are not available for therapeutic drug monitoring.

A search for new CYP3A4 variants as determinants of tacrolimus dose requirements in renal-transplanted patients

The CYP3A5*3 and CYP3A4*1B alleles have been related with tacrolimus (Tac) dose requirements. The rare CYP3A4*22 variant has also been associated with a significantly lower Tac dose. We genotyped the three single-nucleotide polymorphisms in 206 kidney-transplanted patients who received Tac as the primary immunosuppressor. CYP3A5*1 and CYP3A4*1B allele carriers received a significantly higher Tac dose (P<0.01) compared with wild-type homozygotes. We did not find significant differences between the CYP3A4*22 genotypes, either nominally or according to the CYP3A5 genotype (expressers vs. nonexpressers). Sequencing of CYP3A4 coding exons in a total of 15 patients revealed only one nonreported missense change (p.P227>T) in one patient. We concluded that CYP3A5*3 and CYP3A4*1B were the main determinants of the Tac dose-adjusted blood concentration in our cohort of renal-transplanted patients.

PP214—Tacrolimus Blood Concentration in Patients Subjected to Renal Transplantation: The Influence of Gender

Tacrolimus, a potent immunosuppressant, is used for the prevention of allograft rejection in organ transplantation. Tacrolimus trough concentration (TTC) is still widely used as a guide to individualizing tacrolimus dose requirements in renal transplantation. The aim was to investigate the effect of patient’s gender on TTC in renal transplant recipients on quaternary immunosuppressive therapy (tacrolimus, mycophenolate mofetil, prednisone, and anti–T lymphocyte globulin).

Tacrolimus Dose Requirement in Pediatric Liver Transplantation: Influence of CYP3A5 Gene Polymorphism

Little information is available regarding the influence of CYP3A5 genetic polymorphisms on tacrolimus dose requirement in pediatric liver transplantation. We performed a retrospective study among 179 pediatric liver recipients grafted between 2002 and 2009 in order to determine the influence of donor CYP3A5 genotype along with clinical variables on tacrolimus daily dose requirement during the first weeks following transplantation. Mean stable tacrolimus daily dose requirement was higher among children who received a liver expressing CYP3A5 (carrying the CYPA3A5*1 allele) compared with those with a liver that did not express CYP3A5 (CYP3A5*3/*3 genotype): 0.29 ± 0.20 vs 0.18 ± 0.13 mg.kg(-1).d(-1), p = 0.005, respectively. A younger recipient age and fluconazole prescription were also significantly associated with tacrolimus daily dose requirement. Time to reach stable tacrolimus therapeutic trough concentrations was prolonged among patients with a CYP3A5-expressing graft (26 vs 21 days, p = 0.04). Donor CYP3A5 genotype partially explains tacrolimus dose requirement. Original submitted 30 January 2013; Revision submitted 2 May 2013.