Impact of trough abiraterone level on adverse events in patients with prostate cancer treated with abiraterone acetate.

PURPOSE: We assessed the impact of plasma trough concentrations of abiraterone (ABI) and its metabolite Δ4-abiraterone (D4A) and related polymorphisms on adverse events (AEs) in patients with metastatic prostate cancer who received abiraterone acetate (AA). METHODS: This prospective study enrolled patients with advanced prostate cancer treated with AA between 2016 and 2021. Plasma trough concentrations of ABI and D4A were measured using high-performance liquid chromatography. The impact of HSD3B1 rs1047303, SRD5A2 rs523349, and cytochrome P450 family 3A member 4 rs2242480 polymorphisms on plasma concentrations of ABI and D4A and the incidence of AEs were also assessed. RESULTS: In 68 patients treated with AA, the median ABI and D4A concentrations were 18.1 and 0.94 ng/mL, respectively. The high plasma trough concentration of ABI (≥ 20.6 ng/mL) was significantly associated with the presence of any AE and its independent risk factor based on multivariable analysis (odds ratio, 7.20; 95% confidence interval (CI): 2.20-23.49). Additionally, a high plasma trough concentration of ABI was an independent risk factor of time to withdraw AA (hazard ratio, 4.89; 95% CI: 1.66-14.38). The risk alleles of three polymorphisms were not statistically associated with the ABI and D4A concentrations and the incidence of AEs. CONCLUSIONS: The plasma trough concentration of ABI is associated with the presence of AEs and treatment failure after AA administration. ABI concentration monitoring may be useful in patients with prostate cancer who received AA.

Effects of NR1I2 and ABCB1 Genetic Polymorphisms on Everolimus Pharmacokinetics in Japanese Renal Transplant Patients.

The purpose of this study was to evaluate the effects of NR1I2 (7635G>A and 8055C>T) and ABCB1 (1236C>T, 2677G>T/A, and 3435C>T) genetic polymorphisms on everolimus pharmacokinetics in 98 Japanese renal transplant patients. On day 15 after everolimus administration, blood samples were collected just prior to and 1, 2, 3, 4, 6, 9, and 12 h after administration. The dose-adjusted area under the blood concentration−time curve (AUC0-12) of everolimus was significantly lower in patients with the NR1I2 8055C/C genotype than in those with other genotypes (p = 0.022) and was significantly higher in male patients than female patients (p = 0.045). Significant correlations between the dose-adjusted AUC0-12 of everolimus and age (p = 0.001), aspartate transaminase (p = 0.001), and alanine transaminase (p = 0.005) were found. In multivariate analysis, aging (p = 0.008) and higher alanine transaminase levels (p = 0.032) were independently predictive of a higher dose-adjusted everolimus AUC0-12. Aging and hepatic dysfunction in patients may need to be considered when evaluating dose reductions in everolimus. In renal transplant patients, management using everolimus blood concentrations after administration may be more important than analysis of NR1I2 8055C>T polymorphism before administration.

Tacrolimus concentrations after renal transplantation in a mother-neonate dyad: Maternal, neonatal and breast milk measurements.

WHAT IS KNOWN AND OBJECTIVE: We aim to add to the few reports on tacrolimus concentrations in breast milk and in maternal, umbilical vein and neonatal blood after maternal renal transplantation. CASE SUMMARY: In a 30-year-old pregnant woman, the tacrolimus concentration at delivery was the same in maternal, umbilical vein and neonatal blood. The breast milk/maternal blood tacrolimus ratio ranged from 0.40 to 0.64. WHAT IS NEW AND CONCLUSION: The maternal and neonatal blood tacrolimus concentrations at birth are equivalent; thus, one must assume that maternal tacrolimus concentrations directly affect the foetus and/or neonate. Tacrolimus is not detectable in the neonate 3 weeks after birth, suggesting that there is minimal transfer through breast milk.

A comparison of the effects of CYP3A5 polymorphism on tacrolimus blood concentrations measured by 4 immunoassay methods in renal transplant patients.

WHAT IS KNOWN AND OBJECTIVE: The anti-tacrolimus antibodies used in commercial immunoassay methods have cross-reactivity with tacrolimus metabolites. The aim of this study was to investigate differences in the effects of CYP3A5 polymorphism on tacrolimus concentrations obtained by four immunoassay methods in renal transplant patients. METHODS: Samples (n = 508) were evaluated using four immunoassays (chemiluminescence enzyme immunoassay [CLIA], affinity column-mediated immunoassay [ACMIA], electrochemiluminescence immunoassay [ECLIA] and latex agglutination turbidimetric immunoassay [LTIA]). RESULTS: Bland-Altman plots showed average biases of -0.12 (±1.96 SD: -1.30-1.05) ng/mL for CLIA, -0.30 (-1.59-1.00) ng/mL for ECLIA, 0.42 (-1.21-2.05) ng/mL for ACMIA and 1.88 (-0.51-4.28) ng/mL for LTIA, when considering the mean of the three immunoassays (CLIA, ECLIA and ACMIA). In multiple regression analysis, the difference (CLIA-mean) was affected by haematocrit levels. Differences in ECLIA were correlated with red blood cell counts. For LTIA, CYP3A5 genotype and haematocrit levels were identified as independent predictors for this bias. WHAT IS NEW AND CONCLUSION: The results obtained by CLIA, ECLIA and ACMIA were not affected by CYP3A5 polymorphism. However, in LTIA, CYP3A5*1/*3-derived data exhibited an inverse relationship in Bland-Altman analysis (slope: -0.0824). Higher cross-reactivity with 12-hydroxy tacrolimus at lower concentrations may occur in patients with the CYP3A5*1/*3 genotype. Because patients with the CYP3A5*1 allele identified using LTIA may show higher blood concentrations of tacrolimus at lower target concentrations, for example 3.0 ng/mL, compared with other immunoassay methods, there is a need for sufficient consideration of the interpretation of values measured by LTIA.

Prediction of Tacrolimus Exposure by CYP3A5 Genotype and Exposure of Co-Administered Everolimus in Japanese Renal Transplant Recipients.

While tacrolimus and everolimus have common metabolic pathways through CYP3A4/5, tacrolimus is metabolized solely by CYP3A4 in recipients with the CYP3A5*3/*3. The purpose of this study was to evaluate how the area under the blood concentration-time curves (AUC) of tacrolimus could be predicted based on CYP3A5 genotype and the AUC of everolimus in renal transplant patients taking both drugs. The dose-adjusted AUC (AUC/D) of tacrolimus and everolimus were calculated at one month and one year after transplantation. Significant correlations between the AUC/D of tacrolimus and everolimus were found for patients with the CYP3A5*1 allele or CYP3A5*3/*3 at both one month and one year. At both stages, the determination coefficients were higher and the slopes of regression equations were larger for patients with CYP3A5*3/*3 compared to the CYP3A5*1 allele. A good correlation between single doses of tacrolimus and everolimus was found for CYP3A5*3/*3 patients at 1 year after transplantation (r = 0.794, p < 0.001). The variability of the AUC0-24/D of tacrolimus for each CYP3A5 genotype could be predicted based on the AUC0-12/D of everolimus. Clinicians may be able to comprehensively carry out the dose adjustments of tacrolimus and everolimus based on relationship with AUCs of both drugs in each CYP3A5 genotype.

Clinical effects of single nucleotide polymorphisms on drug-related genes in Japanese metastatic renal cell carcinoma patients treated with sunitinib.

Although sunitinib is a well-established chemotherapeutic for metastatic renal cell carcinoma (mRCC), there are no robust markers that predict efficacy and toxicity. We analyzed the effect of single nucleotide polymorphisms (SNPs) in genes involved in sunitinib pharmacokinetics on clinical outcomes in Japanese patients with mRCC. We analyzed the effect of SNPs in genes involved in sunitinib pharmacokinetics on the clinical outcome in mRCC patients in a Japanese population. We evaluated seven SNPs in four candidate genes, the transport proteins ATP-binding cassette (ABC) B1 (rs1045642, rs1128503, rs2032582, and rs7779562) and ABCG2 (rs2231142), and the metabolic proteins cytochrome P450 (CYP) 3A4 (rs35599367) and CYP3A5 (rs776746) in 70 patients. No significant association was observed between the genotypes of each SNP and time to dose reduction, progression-free survival, overall survival, and best objective response. Meanwhile, the incidence of grade 2 or greater hypertension and hand-foot syndrome, and multiple adverse events (>3), was significantly higher in patients carrying the ABCB1 rs2032582 GG genotype [odds ratio (OR): 5.37, 95% confidence interval (CI) 1.02-14.63, P=0.035; OR: 3.17, 95% CI 1.06-9.52, P=0.036, OR: 3.35; 95% CI 1.14-9.84; P=0.025, respectively]. In conclusion, our data showed that the ABCB1 rs2032582 GG genotype was associated with individual adverse events' susceptibility among Japanese patients treated with sunitinib in routine clinical settings.

Impact of the CYP3A5 genotype on the distributions of dose-adjusted trough concentrations and incidence of rejection in Japanese renal transplant recipients receiving different tacrolimus formulations.

BACKGROUND: We investigated the impact of the CYP3A5 genotype on the distributions of dose-adjusted trough concentrations (C 0h/D) and the incidence of rejection in Japanese recipients taking twice-daily (Tac-BID, n = 140) or modified-release once-daily (Tac-QD, n = 80) tacrolimus formulations for 1 year after renal transplantation. METHODS: Logistic regression analysis was carried out to estimate the distinction rate of CYP3A5 genotypes based on the C 0h/D of Tac-BID or Tac-QD. The coefficients of variation (%CVs) were compared in each recipient to estimate the stability of tacrolimus C 0h/D between formulations or CYP3A5 genotypes. RESULTS: Recipients with at least one CYP3A5*1 wild-type allele (EMs) and recipients with homozygous expression of the variant allele CYP3A5*3 (PMs) were significantly identified using the tacrolimus C 0h/D cut-off values of 2.77 and 0.85 ng/mL/mg, respectively, and discrimination rates of 75.3 and 85.4%, respectively, for Tac-BID and Tac-QD groups. The %CV of the tacrolimus C 0h/D in CYP3A5 EMs taking Tac-QD was significantly lower than that in those taking Tac-BID (20.4 versus 23.3%, P = 0.003). The %CV of the tacrolimus C 0h/D was an independent risk factor for rejection (odds ratio = 1.028, P = 0.033). CONCLUSIONS: The tacrolimus C 0h/D values with definite cut-offs for CYP3A5 genotypes were specifically identified in Japanese renal transplant recipients taking Tac-QD. In addition, a larger %CV for the tacrolimus C 0h/D correlated with the incidence of rejection. Consequently, the stability of the C 0h/D achieved using Tac-QD, which was clearly influenced by the CYP3A5 polymorphism, may prevent the development of rejection.

Effect of hepatic drug transporter polymorphisms on the pharmacokinetics of mycophenolic acid in patients with severe renal dysfunction before renal transplantation.

1. The objective of this study was to examine the association of UGT1A9, SLCO, and ABCC polymorphisms with mycophenolic acid (MPA) pharmacokinetics in ABO blood type (ABO) incompatible patients with severe renal dysfunction pre-transplantation. 2. In all patients, on day 14 after beginning mycophenolate mofetil (MMF) treatment (1 week before transplantation) and on day 28 after renal transplantation, samples were collected just prior to and 1, 2, 3, 4, 6, 9, and 12 h after oral MMF administration. 3. The median dose-adjusted AUC0-12 of MPA after renal transplantation was significantly lower than before transplantation (57.9 versus 76.5 µg h/mL, respectively, p = 0.002). 4. Although the enterohepatic circulation of MPA pre-transplantation was extremely high (57.6%), this level was significantly reduced after renal transplantation (34.6%). 5. In the multivariate analysis, pre-transplantation, patients with the SLCO1B3 334T allele (p = 0.003), higher alanine aminotransferase (p = 0.002), and lower body weight were independently predictive for a higher dose-adjusted AUC0-12 of MPA. 6. In patients with severe renal dysfunction pre-transplantation, MPA is excreted mainly to bile from the liver, and as a consequence, the SLCO1B3 334T > G polymorphism was found to be significantly associated with MPA exposure.

Influence of everolimus on the pharmacokinetics of tacrolimus in Japanese renal transplant patients.

OBJECTIVES: To examine whether a trough concentration of everolimus in the therapeutic range of 3-5 ng/mL affects the pharmacokinetics of tacrolimus in renal transplant patients. METHODS: A total of 52 Japanese renal transplant patients receiving tacrolimus were enrolled in this study. In 28 of them, everolimus was co-administered on day 14 after surgery. Changes in the dose-adjusted blood trough concentration of tacrolimus from day 14 to 28 after surgery were investigated. RESULTS: The dose-adjusted blood trough concentration of tacrolimus on day 28 was affected by CYP3A5*3/*3 and hemoglobin level (P < 0.001 and P = 0.007), but not by everolimus (P = 0.171). In addition, there was no change in the dose-adjusted blood trough concentration of tacrolimus in patients before or after everolimus coadministration (P = 0.165). On day 28, there was no correlation between the rate of change in the dose-adjusted blood trough concentration of tacrolimus and the blood trough concentration or area under the plasma concentration-time curve from 0 to 12 h for everolimus after initiation of combination therapy (r = 0.341, P = 0.076 and r = 0.234, P = 0.231). CONCLUSIONS: A pharmacokinetic interaction between tacrolimus and everolimus was not observed clinically in renal transplant patients. Safe and reliable immunosuppressive therapy in renal transplant patients might be achieved using a combination of tacrolimus and everolimus.

Capability of utilizing CYP3A5 polymorphisms to predict therapeutic dosage of tacrolimus at early stage post-renal transplantation.

While CYP3A5 polymorphisms are used to predict the initial dosage of tacrolimus therapy, the predictive capability of genetic information for dosing at early stage post-renal transplantation is unknown. We investigated the influence of polymorphisms over time. An initial oral dose of modified-release once-daily tacrolimus formulation (0.20 mg/kg) was administered to 50 Japanese renal transplant patients every 24 h. Stepwise multiple linear regression analysis for tacrolimus dosing was performed each week to determine the effect of patient clinical characteristics. The dose-adjusted trough concentration was approximately 70% higher for patients with the CYP3A5*3/*3 than patients with the CYP3A5*1 allele before the second pre-transplantation tacrolimus dose (0.97 (0.78-1.17) vs. 0.59 (0.45-0.87) ng/mL/mg; p < 0.001). The contribution of genetic factors (CYP3A5*1 or *3) for tacrolimus dosing showed increased variation from Day 14 to Day 28 after transplantation: 7.2%, 18.4% and 19.5% on Days 14, 21 and 28, respectively. The influence of CYP3A5 polymorphisms on the tacrolimus maintenance dosage became evident after Day 14 post-transplantation, although the tacrolimus dosage was determined based only on patient body weight for the first three days after surgery. Tacrolimus dosage starting with the initial administration should be individualized using the CYP3A5 genotype information.

A limited sampling strategy to estimate the area under the concentration-time curve of tacrolimus modified-release once-daily preparation in renal transplant recipients.

OBJECTIVES: The aim of this study was to develop a limited sampling strategy to estimate the area under the concentration-time curve (AUC) of a modified-release, once-daily formulation of tacrolimus (Advagraf, Japanese trade name Graceptor) with Japanese renal transplant patients. METHODS: Among the 43 enrolled patients, 23 patients continued to take Graceptor for 1 year. A total of 66 profiles on day 28 and day 365 from the 43 patients were randomly divided into a training group (N = 33) and a validation group (N = 33) without any overlap. RESULTS: The prediction formula for the AUC 0-24 using the single C 12h time point gave the highest correlation with the observed AUC 0-24 (r2 = 0.9057). When 2 sampling times were used, C 0h-C 12h were the best time points for the estimation of the AUC 0-24 (AUC 0-24 = 26.8 + 8.0C 0h + 17.8C 12h, r2 = 0.9221, P < 0.0001). There was no significant difference in the prediction error for the prediction formulas with the C 0h-C 12h combination between CYP3A5 genotypes. The % mean prediction error, % mean absolute error, and % root mean squared prediction error of the prediction formula using C 0h-C 12h were 0.1%, 7.6%, and 8.8%, respectively. CONCLUSIONS: In a hospital setting, a limited sampling strategy using C 0h-C 12h would be applicable to estimating the AUC 0-24 of tacrolimus once daily.

Pharmaceutical and genetic determinants for interindividual differences of tacrolimus bioavailability in renal transplant recipients.

PURPOSE: The pharmacokinetics of orally administered immediate-release, twice-daily (BID) and modified-release, once-daily (QD) formulations of tacrolimus have high interindividual variability. We investigated factors affecting interindividual variability of tacrolimus bioavailability in renal transplant patients. METHODS: Ninety-seven Japanese renal transplant patients (47 patients on tacrolimus BID and 50 patients on tacrolimus QD) were enrolled in this study. The tacrolimus absolute bioavailability was calculated using the area under the concentration-time curve from 0 to 24 h (AUC0-24) after continuous intravenous infusion and oral formulations of tacrolimus in the same recipient. RESULTS: The median (quartile 1-quartile 3) tacrolimus relative bioavailability for recipients with the CYP3A5*1 or CYP3A5*3/*3 alleles was significantly lower for the tacrolimus QD group [9.1 % (6.3-10.7 %) and 15.4 % (11.5-18.7 %), respectively] than for the tacrolimus BID group [12.6 % (9.9-14.2 %) and 19.3 % (16.5-24.8 %), respectively] (P = 0.004 and 0.028, respectively). Consequently, tacrolimus absolute bioavailability was lowest for recipients with the CYP3A5*1 allele taking tacrolimus QD. The CYP3A5 polymorphism had no impact on the dose-adjusted AUC0-24 of tacrolimus in patients on continuous intravenous infusion (P = 0.906). CONCLUSION: The larger interindividual variability of tacrolimus bioavailability for oral formulations appears to be due to the effects of the CYP3A5 polymorphism and the tacrolimus oral formulation. These factors should therefore be taken into account when determining individualized tacrolimus dosing.

Effect of itraconazole on the concentrations of tacrolimus and cyclosporine in the blood of patients receiving allogeneic hematopoietic stem cell transplants.

PURPOSE: The purpose of this study was to investigate the interactions of itraconazole (ITCZ) with orally administered calcineurin inhibitors (CNIs) in Japanese allogeneic hematopoietic stem cell transplant (HSCT) recipients. METHODS: Sixteen HSCT patients (8 patients each receiving tacrolimus or cyclosporine) were enrolled. An ITCZ oral solution was administered from day 30 after the initiation of ITCZ administration as a loading dose. Before the co-administration of ITCZ and CNI and 1 week daily thereafter, whole blood ITCZ and CNI (tacrolimus or cyclosporine) concentrations were measured in samples taken just before (C0h) and 2 h (C2h) after CNI administration. RESULTS: The median dose-adjusted C0h values of tacrolimus and cyclosporine on day 7 after the start of ITCZ co-administration were 5.6- and 2.7-fold higher, respectively, than the corresponding values obtained before the initiation of ITCZ treatment. On day 7 after ITCZ treatment, the mean single dosages of tacrolimus and cyclosporine were reduced to 33.7 and 66.5 % of the dosages before ITCZ co-administration, respectively, to adjust the CNI target concentration. Although ITCZ co-administration did not alter the dose-adjusted C0h values of tacrolimus in a patient with a CYP3A5 1/ 1 allele, it did change this value of tacrolimus in patients with CYP3A5 3 alleles. However, in patients receiving cyclosporine, no such tendency was observed. CONCLUSION: The magnitude of the interaction between orally administered tacrolimus and ITCZ was significantly greater than that between cyclosporine and ITCZ. Prospective analysis of the CYP3A5 polymorphism may be important to ensure safe and reliable immunosuppressive therapy with tacrolimus in patients treated with ITCZ.

Influence of NAT2 polymorphisms on sulfamethoxazole pharmacokinetics in renal transplant recipients.

The sulfamethoxazole (SMX)-trimethoprim drug combination is routinely used as prophylaxis against Pneumocystis pneumonia during the first 3 to 6 months after renal transplantation. The objective of this study was to examine the impact of N-acetyltransferase 2 (NAT2) and CYP2C9 polymorphisms on the pharmacokinetics of SMX in 118 renal transplant recipients. Starting on day 14 after renal transplantation, patients were administered 400 mg/day-80 mg/day of SMX-trimethoprim orally once daily. On day 14 after the beginning of SMX therapy, plasma SMX concentrations were determined by a high-performance liquid chromatography method. The SMX area under the concentration-time curve from 0 to 24 h (AUC(0-24)) for 15 recipients with the NAT2 slow acetylator genotype (NAT2 5/ 6, - 6/ 6, - 6/ 7, and - 7/ 7) was significantly greater than that for 56 recipients with the NAT2 rapid acetylator genotype (homozygous for NAT2 4) (766.4 ± 432.3 versus 537.2 ± 257.5 µg-h/ml, respectively; P = 0.0430), whereas there were no significant differences in the SMX AUC(0-24) between the CYP2C9 1/ 1 and - 1/ 3 groups. In a multiple regression analysis, the SMX AUC(0-24) was associated with NAT2 slow acetylator polymorphisms (P = 0.0095) and with creatinine clearance (P = 0.0499). Hepatic dysfunction in NAT2 slow acetylator recipient patients during the 6-month period after SMX administration was not observed. SMX plasma concentrations were affected by NAT2 polymorphisms and renal dysfunction. Although standard SMX administration to patients with NAT2 slow acetylator polymorphisms should be accompanied by monitoring for side effects and drug interaction effects from the inhibition of CYP2C9, SMX administration at a low dose (400 mg) as prophylaxis may not provide drug concentrations that reach the level necessary for the expression of side effects. Further studies with a larger sample size should be able to clarify the relationship between SMX plasma concentration and side effects.

Monitoring of mycophenolic acid predose concentrations in the maintenance phase more than one year after renal transplantation.

BACKGROUND: Routine therapeutic drug monitoring of mycophenolic acid (MPA) is generally performed using the area under the concentration-time curve from 0 to 12 hours (AUC0-12) with recommended values between 30 and 60 µg·h/mL. OBJECTIVE: The aim of this study was to examine whether the monitoring of the MPA predose concentration (C0) in patients who are stable for >1 year after renal transplantation was practical and to determine factors that cause MPA C0 variability among patients. METHODS: Eighty-six Japanese patients who had undergone renal transplantation and were taking tacrolimus and who had their MPA C0 analyzed >6 times by high-performance liquid chromatography for >1 year posttransplantation were enrolled. RESULTS: Recipients with MPA AUC0-12 levels<30 µg·h/mL on day 28 and 1 year after transplantation had an MPA C0 of <2.0 µg/mL, with a sensitivity of 90.9% and a specificity of 70.7%. There was no significant difference in the mean dose-adjusted MPA C0>1 year after transplantation between subjects with either the UGT (1A1, 1A9, and 2B7) or drug transporter (SLCO1B3, ABCC2, and ABCG2) genotypes. However, in a multiple regression analysis, the dose-adjusted mean MPA C0>1 year after transplantation was significantly associated with age (P=0.0035), creatinine clearance (P=0.0001), and the dose-adjusted MPA AUC0-12 at 1 year (P=0.0147). CONCLUSIONS: To keep the MPA AUC0-12>30 µg·h/mL, the plasma threshold for maintaining the MPA C0 with tacrolimus should be set >2.0 µg/mL as determined by high-performance liquid chromatography. For patients who are stable for >1 year after transplantation, continued monitoring of the MPA C0 using the same samples used to monitor the tacrolimus C0 and the additional assessment of the MPA AUC0-12 at the 1-year time point seem to be a viable option. If a change of the mycophenolate mofetil dose seems necessary based on the routine MPA C0 information, the determination of MPA AUC0-12 using a limited sampling strategy is recommended.

Simultaneous determination of warfarin and 7-hydroxywarfarin enantiomers by high-performance liquid chromatography with ultraviolet detection.

Warfarin is administered clinically as a racemic mixture of two enantiomers, (R)-warfarin and (S)-warfarin. (S)-Warfarin has more potent anticoagulant activity than (R)-warfarin and is metabolized mainly to (S)-7-hydroxywarfarin by CYP2C9. A simple, rapid, and sensitive high-performance liquid chromatography method with ultraviolet detection was developed for the simultaneous quantitative determination of the (R)- and (S)-enantiomers of warfarin and 7-hydroxywarfarin in human plasma. Analytes and the internal standard (p-chlorowarfarin) were separated using a mobile phase of 0.5% KH2PO4 (pH 3.5)-methanol (41:59, v/v) on a Chiral CD-Ph column at a flow rate of 0.5 mL/min and were detected at a ultraviolet absorbance of 305 nm. Analysis required 200 µL of plasma and involved a simple and rapid solid-phase extraction with an Oasis HLB cartridge, which gave high recovery (greater than 91.8%) and good selectivity for all analytes. The lower limit of quantification for the (R)- and (S)-enantiomers of warfarin and 7-hydroxywarfarin was 2.5 ng/mL for each analyte. Inter- and intraday coefficients of variation for all analytes were less than 14.2% and accuracies were within 6.6% over the linear range. Our results indicate that this method is applicable to the simultaneous monitoring of the enantiomers of warfarin and 7-hydroxywarfarin in human plasma. The S/R-enantiomer ratio of warfarin and the (S)-warfarin/(S)-7-hydroxywarfarin ratio 3 hours after administration in 67 CYP2C9*1/*1 patients ranged from 0.24 to 0.75 and from 1.83 to 19.02, respectively, whereas these ratios in a CYP2C9*3/*3 patient were 1.12 and 17.02, respectively.

Influence of CYP3A5 and drug transporter polymorphisms on imatinib trough concentration and clinical response among patients with chronic phase chronic myeloid leukemia.

Imatinib mesylate (IM) trough concentration varies among IM-treated chronic myeloid leukemia (CML) patients. Although IM pharmacokinetics is influenced by several enzymes and transporters, little is known about the role of pharmacogenetic variation in IM metabolism. In this study, associations between IM trough concentration, clinical response and 11 single-nucleotide polymorphisms in genes involved in IM pharmacokinetics (ABCB1, ABCC2, ABCG2 CYP3A5, SLC22A1 and SLCO1B3) were investigated among 67 Japanese chronic phase CML patients. IM trough concentration was significantly higher in patients with a major molecular response than in those without one (P=0.010). No significant correlations between IM trough concentration and age, weight, body mass index or biochemical data were observed. However, the dose-adjusted IM trough concentration was significantly higher in patients with ABCG2 421A than in those with 421C/C (P=0.015). By multivariate regression analysis, only ABCG2 421A was independently predictive of a higher dose-adjusted IM trough concentration (P=0.015). Moreover, previous studies have shown that the ABCG2 421C>A (p.Q141K) variant is prevalent among Japanese and Han Chinese individuals and less common among Africans and Caucasians. Together, these data indicate that plasma IM concentration monitoring and prospective ABCG2 421C>A genotyping may improve the efficacy of IM therapy, particularly among Asian CML patients.

Influence of drug-transporter polymorphisms on the pharmacokinetics of fexofenadine enantiomers.

This study investigated an association of SLCO (encoding organic anion-transporting polypeptides (OATP), 1B1, 1B3, and 2B1), ABCB1 (P-glycoprotein (P-gp)), ABCC2 multidrug resistance protein 2 (MRP2), and ABCG2 (breast cancer resistance protein (BCRP)) polymorphisms with fexofenadine enantiomer pharmacokinetics after an oral dose of fexofenadine (60 mg) in 24 healthy subjects. The area under the plasma concentration-time curve (AUC(0-24)) of S-fexofenadine, but not R-fexofenadine, was significantly lower in subjects with a SLCO2B1*1/*1 allele as compared to subjects with a *3 allele (p = 0.031). The AUC(0-24) of S-fexofenadine was significantly lower in subjects with a wild-type combination of SLCO2B1*1/*1/ABCB1 1236CC, SLCO2B1*1/*1/ABCB1 3435CC, SLCO2B1*1/*1/ABCC2 -24CC, and ABCB1 1236CC/3435CC/ABCC2 -24CC compared to other polymorphic genotypes (p = 0.010, 0.033, 0.022, and 0.036, respectively), whereas there was no difference in the AUC(0-24) between the SLCO1B1/1B3 plus ABCB1 and ABCC2 groups. The pharmacokinetic properties of S-fexofenadine are affected by a single polymorphism of SLCO2B1 in combination with several polymorphisms of ABCB1 C1236T, C3435T, and ABCC2 C-24T. However, the ABCG2 polymorphism was not associated with fexofenadine pharmacokinetics. These findings suggest that a combination of multiple transporters, including OATP, P-gp, and MRP2, reacts strongly to fexofenadine exposure in the small intestine and liver, resulting in different dispositions of both enantiomers.

Changes in PCSK9 and LDL cholesterol concentrations by everolimus treatment and their effects on polymorphisms in PCSK9 and mTORC1.

BACKGROUND: The purpose of this study was to evaluate the effects of concentrations of proprotein convertase subtilisin/kexin type 9 (PCSK9) and low-density lipoprotein (LDL) cholesterol by the mammalian target of rapamycin (mTOR) inhibitor everolimus and their effects on genetic polymorphisms in the PCSK9 and mTORC1 genes in 53 renal transplant recipients. METHODS: Prior to and on day 15 after everolimus administration, the concentrations of everolimus in blood and PCSK9 and LDL cholesterol in plasma were evaluated. Additionally, mTORC1 (rs2536T>C and rs2295080T>G) and PCSK9 (rs505151G>A, rs562556G>A, and rs11593680C>T) polymorphisms were analyzed. RESULTS: Mean PCSK9 plasma concentrations on day 15 after everolimus treatment were significantly higher than those before treatment (295 versus 214 ng/mL, respectively; p = 0.004). Significant correlations between the area under the blood concentration-time curves (AUC)0-12 on day 15 of everolimus treatment and the change rate in PCSK9 concentrations were found (r = 0.316, p = 0.021). However, there were no significant correlations between the change rate in PCSK9 and LDL cholesterol concentrations. The change rate in PCSK9 concentrations by everolimus treatment was significantly greater in patients with the mTORC1 rs2295080G allele than the T/T genotype (p = 0.006); however, there were no significant differences between PCSK9 rs505151G>A and rs11583680C>T genotypes. In multivariate analyses, patients with mTORC1 rs2295080G (p = 0.010), higher everolimus AUC0-12 (p = 0.006), and female sex (p = 0.029) showed higher change rates of PCSK9 following everolimus therapy. CONCLUSIONS: Administration of everolimus significantly elevated plasma PCSK9 concentrations, potentially causing everolimus-induced hyperlipidemia.

Early phase limited sampling strategy characterizing tacrolimus and mycophenolic acid pharmacokinetics adapted to the maintenance phase of renal transplant patients.

The aim of this study was to examine whether a limited sampling strategy (LSS) to allow the simultaneous estimation of the area under the concentration-time curves (AUCs) of tacrolimus and mycophenolic acid (MPA) calculated in the early stage after renal transplantation could be applied to maintenance phase pharmacokinetics. Seventy Japanese patients were enrolled. One year after transplantation, samples were collected just before and 1, 2, 3, 4, 6, 9, and 12 hours after tacrolimus and mycophenolate mofetil administration at 9:00 am and at 9:00 pm. The prediction formulas on day 28 (tacrolimus AUC 0-12 = 7.04 x C 0h + 1.71 x C 2h + 3.23 x C 4h + 15.19 and 2.25 x C 2h + 1.92 x C 4h + 7.27 x C 9h + 6.61, and MPA AUC 0-12 = 0.26 x C 0h + 2.06 x C 2h + 3.82 x C 4h + 20.38 and 1.77 x C 2h + 2.34 x C 4h + 4.76 x C 9h + 15.94) were applied to pharmacokinetic data obtained at 1 year. Three error indices [percent mean prediction error (ME), % mean absolute error, and percent root mean squared prediction error (RMSE)] were used to evaluate the predictive bias, accuracy, and precision. The predicted AUC 0-12 of tacrolimus and MPA at 3 time points, C 2h-C 4h-C 9h, showed higher correlation with the measured AUC 0-12 of tacrolimus and MPA (r2 = 0.817 and 0.789, respectively) in comparison with those at C 0h-C 2h-C 4h. The values for the prediction formulas for tacrolimus AUC at 1 year using the C 2h-C 4h-C 9h combination yielded less than 5% for %ME and 15% for %RMSE. The %ME and %RMSE values of the prediction formulas for tacrolimus AUC using the C 0h-C 2h-C 4h combination were 6.3% and 15.9%, respectively. The %ME and %RMSE values of the prediction formulas for MPA AUC at 1 year using the C 0h-C 2h-C 4h combination were 5.9% and 25.8%, respectively, and those for the C 2h-C 4h-C 9h combination were 4.9% and 21.2%, respectively. AUC 6-12/AUC 0-12 of MPA 1 year after transplantation was significantly lower than 28 days after transplantation. An LSS using C 2h-C 4h-C 9h seems to be applicable for predicting the AUC of tacrolimus and MPA at either posttransplantation stage. The enterohepatic circulation of MPA was significantly reduced 1 year after transplantation. Therefore, 1 year after transplantation, the estimation of the AUC 0-12 of MPA for the C 0h-C 2h-C 4h equations was imprecise. It is important that the LSS includes C 9h because it contains information on the secondary plasma peak of MPA.