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Pharmacokinetics of Bosentan in Routinely Treated Japanese Pediatric Patients with Pulmonary Arterial Hypertension
Drug Metab. Pharmacokinet. 26 (3): 280287 (2011).
Copyright © 2011 by the Japanese Society for the Study of Xenobiotics (JSSX)
Regular Article Pharmacokinetics of Bosentan in Routinely Treated Japanese Pediatric Patients with Pulmonary Arterial Hypertension Masato TAGUCHI 1 , Fukiko I CHIDA 1 , Keiichi H IRONO 1 , Toshio M IYAWAKI 1 , Naoki YOSHIMURA 1 , Tsuneyuki N AKAMURA 2, Chisato A KITA 2, Tomotaka N AKAYAMA 3 , Tsutomu S AJI 3 , Yuya K ATO 1 , Isao H ORIUCHI 1 and Yukiya H ASHIMOTO 1, * 1 Graduate
School of Medicine and Pharmaceutical Sciences, University of Toyama, Toyama, Japan 2 Department of Pediatrics, Kanazawa Medical University, Kahoku, Japan 3 Department of Pediatrics, Faculty of Medicine, Toho University Medical Center, Omori Hospital, Tokyo, Japan
Full text of this paper is available at http://www.jstage.jst.go.jp/browse/dmpk Summary: We evaluated the pharmacokinetics of routinely administered bosentan in 46 Japanese pediatric patients with pulmonary arterial hypertension. Plasma samples were taken twice at times corresponding to the peak and trough concentrations following repetitive oral administration. The population pharmacokinetic parameters of bosentan were estimated by use of the NONMEM program, in which a onecompartment model with repetitive bolus dosing was parameterized in terms of the oral clearance (CL/F) and elimination rate constant (k). Polymorphisms of CYP3A5, SLCO1B1, SLCO1B3, and SLCO2B1 had no significant effect on the disposition of bosentan. In addition, the pharmacokinetics of bosentan was not altered by heart failure or coadministration of sildenafil. In contrast, weight (WT)-normalized values of CL/F were correlated negatively with age (AGE). The final population mean values of CL/F and k were estimated to be 0.409 · (1 ¹ 0.0377 · (AGE ¹ 3.81)) · WT L/h and 0.175 h ¹1 , respectively. Keywords: bosentan; pharmacokinetics; pediatric patients; pulmonary arterial hypertension; genetic polymorphisms; organic anion transporting polypeptide; cytochrome P450
of bosentan with cyclosporine, a potent inhibitor of OATPs, is contraindicated owing to risk of greatly increased bosentan levels.3¥ In addition, we have previously demonstrated that OATP substrates ¤taurocholic acid or bilirubin¥ significantly attenuate the hepatic clearance of bosentan in rats.5¥ The genetic polymorphisms of CYP2C9 have been extensively studied, and CYP2C9*1 ¤wild-type¥ and CYP2C9*3 were identified in a Japanese population.6¥ CYP2C9*3 ¤1075AhC¥ is an allelic variant in exon 7 that produces an enzyme with an Ile359/Leu359 amino acid substitution, leading to an impairment in the enzymatic activity of CYP2C9.7¥ The allele frequency of CYP2C9*3 among the Japanese is reported to be only 2.1%.6¥ In contrast, more than 30 single nucleotide polymorphisms ¤SNPs¥ have been identified in the CYP3A4 gene.8¥ For the most common variant, CYP3A4*1B, increased transcription was demonstrated in vitro, which may theoretically result in greater enzymatic activity in vivo.9¥ However, the allele
Introduction Bosentan is a potent nonpeptidic endothelin receptor antagonist with high affinity for both endothelin A and B receptors; it is usually administered orally twice a day to patients with pulmonary arterial hypertension.1¥ Bosentan is eliminated predominantly by hepatic metabolism, with renal excretion accounting for only 0.9% of the administered dose.2¥ After single intravenous administration of bosentan at a dose of 250 mg to healthy male subjects, the amounts of hydroxy-, phenolic-, and hydroxy-phenolic metabolites excreted into feces within 5 days were 47.5%, 6.4%, and 17.7% of the dose, respectively.2¥ The formation of these major bosentan metabolites is catalyzed by cytochrome P450 ¤CYP¥ 2C9 and CYP3A4 in the human liver.3¥ On the other hand, Treiber et al.4¥ reported that bosentan is a substrate of human organic anion transporting polypeptide ¤OATP¥ 1B1, OATP1B3, and OATP2B1, which are expressed on the sinusoidal membrane in the human liver. Coadministration
Received; November 7, 2010, Accepted; February 8, 2011 J-STAGE Advance Published Date: March 4, 2011, doi:10.2133/dmpk.DMPK-10-RG-113 *To whom correspondence should be addressed: Yukiya HASHIMOTO, Ph.D., Graduate School of Medicine and Pharmaceutical Sciences, University of Toyama, 2630 Sugitani, Toyama 930-0194, Japan. Tel. +81-76-434-7585, Fax. +81-76-434-7586, E-mail: [email protected] 280
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Pharmacokinetics of Bosentan in Japanese Pediatric Patients
frequency of CYP3A4*1B was found to be extremely low in the Japanese.8¥ CYP3A5 is another important CYP3A protein in the liver and exhibits significant overlap with CYP3A4 in substrate specificity.10¥ The defective allelic variant, CYP3A5*3 ¤6986AhG¥, was frequently observed in a Japanese population.11¥ Several sequence variations and their haplotypes have been discovered in the solute carrier organic anion transporter ¤SLCO¥ 1B1, SLCO1B3, and SLCO2B1 genes encoding OATP1B1, OATP1B3, and OATP2B1, respectively.12®17¥ It has been reported that the SLCO1B1 521ThC allele is associated with increased plasma concentration of the endothelin I receptor antagonist atrasentan.12¥ That is, the geometric mean for the area under the plasma concentration®time curve during a dose interval ¤AUCØ¥ of atrasentan in patients with the SLCO1B1 521TC genotype was 14% higher than that in patients with the 521TT genotype.12¥ The allele frequency of SLCO1B1 521ThC among Japanese was reported to be 11.0%.13¥ Recently, it was also reported that the genotype of SLCO1B3 and SLCO2B1 affected the pharmacokinetics of digoxin and montelukast, respectively.14,15¥ The main purpose of the present study was to evaluate the pharmacokinetics of bosentan in Japanese pediatric patients and to investigate the effects of CYP3A5, SLCO1B1, SLCO1B3, and SLCO2B1 ¤and, if possible, CYP2C9¥ genotypes on the pharmacokinetics of bosentan. Pharmacokinetic analysis was performed using a nonlinear mixedeffects model ¤NONMEM¥ program, because population pharmacokinetics based on NONMEM analysis can simultaneously evaluate the mean pharmacokinetic parameters, the covariates affecting the pharmacokinetics of a drug, and also unknown inter- and intra-individual pharmacokinetic variability.18¥ Methods Subjects and study protocols: Forty-six Japanese pediatric patients with pulmonary arterial hypertension ¤29 boys and 17 girls¥ participated in this study, and their demographic and clinical data are summarized in Table 1. The patients ranged in age from 25 days to 16.9 years old, and in body weight from 3.5 to 57.0 kg. In addition, 26 patients had undergone cardiac surgery and 10 patients were characterized as having Downös syndrome. Although no patients had severe hepatic or renal failure, 24 patients had severe chronic heart failure. That is, the N-terminal probrain natriuretic peptide ¤NT-proBNP¥ concentration was above 400 pg/mL ¤normal range: 0®125 pg/ml¥ in 15 of 20 patients, and the brain natriuretic peptide ¤BNP¥ concentration was above 100 pg/mL ¤normal range: 0®18.4 pg/mL¥ in 9 of 26 patients. The patients were routinely treated with oral administration of bosentan hydrate ¤Tracleer tablet, Actelion Pharmaceuticals, Tokyo, Japan¥. Bosentan was administered twice a day to 45 patients and three times a day to 1 patient. The dose of bosentan was
Table 1. Demographics of 46 Japanese pediatric patients with pulmonary arterial hypertension Age ¤year¥
3.81 + 4.79 ¤25 days to 16.9 years¥
Body weight ¤kg¥
13.4 + 12.6 ¤3.5®57.0¥
Sex Number of males
29 patients
Number of females
17 patients
Bosentan dose ¤mg/kg/day¥
2.34 + 0.80 ¤0.49®4.78¥
Blood sampling time after dose ¤h¥ Peak
3.1 + 0.3 ¤2.8®4.0¥
Trough
12.9 + 2.2 ¤8.0®17.3¥
Natriuretic peptides ¤pg/mL¥ NT-proBNP ¤n © 20¥
1509 + 3646 ¤119®16855¥
BNP ¤n © 26¥
112 + 161 ¤ND* to 762¥
Concomitant drug Furosemide
40 patients
Spironolactone
39 patients
Beraprost
30 patients
Aspirin
23 patients
Enalapril
21 patients
Warfarin
20 patients
Sildenafil
15 patients
Digoxin
10 patients
Carvedilol
6 patients
Values are expressed as mean + S.D. ¤range¥ unless specified otherwise. *ND: not detected.
based solely on clinical considerations, and the mean daily dose was 2.34 + 0.80 mg/day/kg. Most patients took multiple drugs concomitantly with bosentan, but no patients had concomitant medication known to potently inhibit CYP2C9, CYP3A4/5, or OATP activity ¤e.g. amiodarone, ketoconazole, or cyclosporine¥. Two blood samples ªjust before the dose, corresponding to trough concentrations ¤Ctrough¥, and at 2.8®4.0 h after the dose, corresponding to peak concentrations ¤Cpeak¥« were withdrawn from each patient at steady state following repetitive dosing for more than 4 weeks ¤Table 1¥. Blood sampling was performed on the same day ¤in 21 outpatients and 14 inpatients¥ or on different days ¤in 11 outpatients¥. The patients and/or their family members gave written informed consent to participate in this study, which was approved by the ethics committee of the University of Toyama ¤#EG19-3¥. Genotyping of drug metabolizing enzymes and transporters: Genomic DNA was isolated from the peripheral blood with an extraction kit ¤QIAGEN, Hilden, Germany¥. Polymorphisms of CYP2C9 ¤1075AhC; rs1057910¥ and SLCO1B3 ¤334ThG; rs4149117¥ were determined by the polymerase chain reaction-restriction fragment length polymorphism ¤PCR-RFLP¥ method as described previously.6,16¥ A polymorphism of SLCO1B1 ¤521ThC; rs4149056¥ was detected by using the allele-
Copyright © 2011 by the Japanese Society for the Study of Xenobiotics (JSSX)
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Masato TAGUCHI, et al.
Table 2. Genotypes of CYP2C9, CYP3A5, SLCO1B3, and SLCO2B1 in 46 patients Gene
SNP
Location
CYP2C9
1075AhC
Exon 7
CYP3A5
6986AhG Intron 3
rs #
SLCO1B1,
CL=Fi ¼ Í 1 WTi expðÌCL=Fi Þ
Genotype Group 1
Group 2
Group 3
rs1057910 A/A ¤45¥ A/C ¤1¥ rs776746
A/A ¤2¥ G/G ¤27¥ A/G ¤17¥
SLCO1B1
521ThC
Exon 5
rs4149056 T/T ¤38¥
SLCO1B3
334ThG
Exon 3
rs4149117
T/C ¤8¥
T/T ¤1¥ G/G ¤26¥ T/G ¤19¥
SLCO2B1
935GhA
Exon 7
rs12422149 G/G ¤23¥ G/A ¤15¥ A/A ¤8¥
Figures shown in parentheses indicate the number of patients.
specific PCR amplification method.13¥ In contrast, polymorphisms of CYP3A5 ¤6986AhG; rs776746¥ and SLCO2B1 ¤935GhA; rs12422149¥ were determined by direct sequencing.15,19¥ In the present study, the patients were divided into two or three groups according to the genotypes of each drug metabolizing enzyme or transporter ¤Table 2¥. Assay of bosentan: Plasma concentrations of bosentan were determined by a reversed-phase HPLC method.5¥ The HPLC system consisted of an LC-10Avp Liquid Chromatograph Series ¤Shimadzu, Kyoto, Japan¥ with a model SPD-10Avp UV-visible detector ¤Shimadzu¥ and the Inertsil ODS-3 column ¤15 cm ' 4.6 mm i.d.; 3 µm particle size; GL Sciences, Tokyo, Japan¥. The mobile phase was acetonitrile and 5 mM CH3COONH4 adjusted to pH 2.69 with acetic acid ¤41/59, v/v¥. A 0.3-mL aliquot of plasma samples was acidified with 1.2 mL of 1 M citrate buffer ¤pH 4.0¥, and mildly extracted with 5 mL of a mixture of nbutyl chloride and dichloromethane ¤4/1, v/v¥. The organic phase was then evaporated to dryness with a SpeedVac system ¤Savant, Famingdale, NY, U.S.A.¥. The residue was dissolved in 200 µL of mobile phase, and 150 µL was injected into the column. The flow rate of the mobile phase was 1.0 mL/min, and the column temperature was 40ôC. Peaks were monitored at 270 nm, and the retention time was 24 min for bosentan. The quantitation limit for bosentan was a plasma concentration of 5 ng/mL. In addition, the coefficient of intra-day variation of this assay was 3.8% and 2.5% at plasma bosentan concentrations of 200 and 2000 ng/mL, respectively. Population pharmacokinetic analysis: The time required to reach the peak concentration after oral administration of a conventional preparation of bosentan is short ¤median: 3.0 h¥.20¥ In the present study, no plasma concentration data of bosentan was obtained at the absorption phase ¤0®2.8 h after oral administration¥. Therefore, the one-compartment model with repetitive bolus dosing was parameterized in terms of the oral clearance ¤CL/F¥ and the elimination rate constant ¤k¥.21¥ For the simplest base model, the oral clearance in the ith individual ¤CL/Fi¥ was modeled using the following equation:
ð1Þ
where WTi is the individual body weight ¤in kg¥, Í1 & WTi is the predicted population mean of CL/F ¤in L/h¥, and ÌCL=Fi is a random variable distributed normally with a mean of zero and variance of Ý2CL/F. The elimination rate constant in the ith individual ¤ki¥ was modeled using the following equation: ki ¼ Í2 expðÌki Þ
ð2Þ %1
where Í2 is a predicted population mean of k ¤in h ¥, and Ìki is a random variable distributed normally with a mean of zero and variance of Ý2k. Finally, the jth observed plasma concentration in the ith patient ¤Cpij¥ was assumed to be randomly distributed from the jth predicted plasma concentration in the ith patient ¤Cpij ¥: Cpij ¼ Cpij expðÞij Þ
ð3Þ
where Þij is a random variable that describes intraindividual variability with a mean of zero and variance of Ö2. In the present study, the number of blood samplings was only two in each patient, and the Ö2 value was frequently unobtainable. Therefore, the Ö2 value was fixed to 0.0225 ¤i.e., 0.152¥ throughout the study.22¥ We further performed the stepwise forward selection of possible factors ¤variables¥ influencing the pharmacokinetics of bosentan.23,24¥ Table 3 summarizes the 10 analysis models at Stage 1 of the selection. The effect of CYP2C9 genotypes on the CL/F of bosentan was evaluated with Model 1, where G2CYP2C9 © 0 for Group 1 patients with the CYP2C9 1075AA genotype and G2CYP2C9 © 1 for Group 2 patients with the 1075AC genotype. The effect of CYP3A5 genotypes on the CL/F of bosentan was evaluated with Model 2, where G1CYP3A5 © 1 for Group 1 patients with the CYP3A5 6986AA or 6986AG genotype and G1CYP3A5 © 0 for Group 2 patients with the 6986GG genotype. The effect of SLCO1B1 genotypes on CL/F was evaluated with Model 3, where G2SLCO1B1 © 0 for Group 1 patients with the SLCO1B1 521TT genotype and G2SLCO1B1 © 1 for Group 2 patients with the 521TC genotype. The effect of SLCO1B3 genotypes on CL/F was evaluated with Model 4, where G2SLCO1B3 © 0 for Group 1 patients with the SLCO1B3 334TT or 334TG genotype and G2SLCO1B3 © 1 for Group 2 patients with the 334GG genotype. The effect of SLCO2B1 genotypes on CL/F was evaluated with Model 5, where G2SLCO2B1 © 0 and G3SLCO2B1 © 0 for Group 1 patients with the SLCO2B1 935GG genotype, G2SLCO2B1 © 1 and G3SLCO2B1 © 0 for Group 2 patients with the 935GA genotype, and G2SLCO2B1 © 0 and G3SLCO2B1 © 1 for Group 3 patients with the 935AA genotype ¤Table 3¥. The effect of coadministration of sildenafil on CL/F was evaluated using Model 6, where Sildenafil is one for patients taking sildenafil and zero for the other patients. The effect of heart failure on CL/F was evaluated using Model 7, where BNP h100 is one for patients with severe chronic heart failure ¤in which the BNP or NT-proBNP
Copyright © 2011 by the Japanese Society for the Study of Xenobiotics (JSSX)
283
Pharmacokinetics of Bosentan in Japanese Pediatric Patients Table 3. Stepwise forward selection of variables for the oral clearance and elimination rate constant Stage
Model
1
1
CYP2C9 CL=Fi ¼ Í 1 Í G2 WTi expðÌCL=Fi Þ 3
0.06 vs. base model
2
CYP3A5 WTi expðÌCL=Fi Þ CL=Fi ¼ Í 1 Í G1 4
0.04 vs. base model
3
SLCO1B1 WTi expðÌCL=Fi Þ CL=Fi ¼ Í 1 Í G2 5
0.09 vs. base model
4
SLCO1B3 WTi expðÌCL=Fi Þ CL=Fi ¼ Í 1 Í G2 6
0.22 vs. base model
5
CL=Fi ¼ ðÍ 1 þ Í 7 G2SLCO2B1 þ 2 Í 7 G3SLCO2B1 Þ WTi expðÌCL=Fi Þ
3.30~ vs. base model
6
CL=Fi ¼ Í 1 Í Sildenafil WTi expðÌCL=Fi Þ 8
0.07 vs. base model
7
WTi expðÌCL=Fi Þ CL=Fi ¼ Í 1 Í BNP>100 9
8 9 10 2
Formula
LLD
2.17~ vs. base model
CL=Fi ¼ Í 1 ð1
Í 10 ðAGE 3:81ÞÞ WTi expðÌCL=Fi Þ WTi Í11 CL=Fi ¼ Í 1 13:4 expðÌki Þ 13:4 Í12 WTi ki ¼ Í 2 expðÌki Þ 13:4
¡
11
CL=Fi ¼ ðÍ 1 þ Í 7 G2SLCO2B1 þ 2 Í 7 G3SLCO2B1 Þ ð1
12
CL=Fi ¼ Í 1 Í BNP>100 ð1 Í 10 ðAGE 3:81ÞÞ WTi expðÌCL=Fi Þ 9 WTi Í11 CL=Fi ¼ Í 1 13:4 ð1 Í 10 ðAGE 3:81ÞÞ expðÌki Þ 13:4
13
Í 10 ðAGE
6.88* vs. base model 4.38~ vs. base model 0.29 vs. base model 3:81ÞÞ WTi expðÌCL=Fi Þ
4.30 vs. Model 8 1.45 vs. Model 8 1.21 vs. Model 8
*p g 0.01 compared with base model. ~Unselected variables with LLD decreases of h1 at Stage 1 were retained as candidates for selection at Stage 2. ¡The model selected as the final model.
concentration was higher than 100 pg/mL or 400 pg/mL, respectively¥ and zero for the other patients. The effect of age on CL/F was evaluated using Model 8. In addition, the effects of body weight on CL/F and k were evaluated using Models 9 and 10, respectively ¤Table 3¥. Data analysis was performed with the NONMEM software ¤double-precision NONMEM Version V Level 1.1, PREDPP Version IV Level 1.1, and NM-TRAN Version III Level 1.1¥18¥ running on a mainframe UNIX supercomputer at the Kyoto University Academic Center for Computing and Media Studies. In the present study, we used a first-order conditional estimation method and the NONMEM-PREDPP library subroutines ADVAN1 and TRANS1 for the one-compartment model with bolus dosing.18¥ The statistical significance of the model parameter was evaluated with the likelihood ratio test using the minimum value of the objective function ¤%2 log likelihood¥ produced by NONMEM.18,24¥ In the present study, when the %2 log likelihood difference ¤LLD¥ between two models allowing a parameter of interest to be freely estimated versus a fixed hypothetical value was greater than 6.63, the parameter value was considered to be statistically significant ¤p g 0.01¥. In addition, NONMEM provides estimates of the standard error ¤S.E.¥ for all parameters, and S.E. can be used to define 95% confidence intervals ¤CI¥ for true parameter values: 95% CI © ¤the estimated parameter value¥ + 1.96 & S.E.18,24¥ Results The genotypes of CYP2C9, CYP3A5, SLCO1B1, SLCO1B3, and SLCO2B1 in the 46 Japanese pediatric patients are
shown in Table 2. Figure 1 shows the plasma concentrations of bosentan in individual patients. A more than 50-fold difference was observed between the highest and lowest peak concentrations ¤Fig. 1A¥. On the other hand, a large interindividual difference was still observed when the plasma concentrations were corrected for the daily dose of the drug ¤Fig. 1B¥. Table 4 shows the population mean pharmacokinetic parameters of bosentan that were estimated by using the simplest base model. The Í1 and Í2 values were estimated to be 0.401 L/h/kg and 0.175 h%1, respectively. The Ý2CL/F and Ý2k values were estimated to be 0.304 and 0.0868, respectively, indicating the especially large interindividual variation of CL/F ¤Table 4¥. Figure 2A shows the relationship between the observed bosentan plasma concentrations and the respective concentrations predicted by the population mean parameters of the base model. Although the correlation between the observed and predicted concentrations was not very high, the observed concentrations seemed to be distributed randomly from the predicted concentrations. To explore factors influencing the pharmacokinetics of bosentan, the pharmacokinetic parameters in individual patients were estimated by the Bayesian method using a posthoc option of the NONMEM program.18,25¥ Figure 2B shows the relationship between the observed bosentan plasma concentrations and the respective concentrations estimated by Bayesian analysis with population parameters of the base model. The improved correlation in Figure 2B suggested that the pharmacokinetic parameters in individual patients were well estimated by Bayesian analysis. Figure 3 shows the effects of CYP2C9, CYP3A5, SLCO1B1,
Copyright © 2011 by the Japanese Society for the Study of Xenobiotics (JSSX)
284
10000
Plasma conc. (ng/mL)
A 3000 1000 300 100 30 10 3
0
6
12
18
Plasma conc./Dose (kg䡡day/L)
Masato TAGUCHI, et al.
3 B 1 0.3 0.1 0.03 0.01 0.003 0.001
6
0
Time after dose (hr)
12
18
Time after dose (hr)
Fig. 1. Measured peak and trough plasma concentrations (A) and dose-corrected peak and trough plasma concentrations (B) following repetitive oral administration of bosentan
10
1 0.1 0.01 R=0.843
0.001 0.001
0.01
0.1
1
10
10 B
Observed conc. (ng/mL)
A
Observed conc. (ng/mL)
Observed conc. (ng/mL)
10
1 0.1 0.01 R=0.995
0.001 0.001
Predicted conc. (ng/mL)
0.01
0.1
1
Predicted conc. (ng/mL)
10
C
1 0.1 0.01 R=0.886
0.001 0.001
0.01
0.1
1
10
Predicted conc. (ng/mL)
Fig. 2. The relationship between the observed and predicted bosentan concentrations in 46 patients Concentrations predicted using the population mean parameters of the base model (A), using Bayesian analysis with population parameters of the base model (B), and using the population mean parameters of the final model (C)
Table 4. Population pharmacokinetic parameters of bosentan estimated with the base model Parameters
Estimates
95% CI
Í1 ¤L/h/kg¥
0.401
0.333®0.469
Í2 ¤h%1¥
0.175
0.158®0.192
Ý2CL/F
0.304
0.138®0.470
Ý 2k
0.0868
0.0433®0.1303
The simplest base model was modeled using the following equations: CL/Fi © Í1 & WTi & exp¤ÌCL=Fi ¥ and ki © Í2 & exp¤Ìki ¥
SLCO1B3, and SLCO2B1 genotypes on the individual CL/F values of bosentan. The CL/F value in the patient with the CYP2C9 1075AC genotype was estimated to be 0.412 L/ h/kg, which is similar to the population mean parameter, Í1, for the base model ¤Fig. 3A and Table 4¥. CYP3A5 genotypes seemed to have no effect on the CL/F values of bosentan ¤Fig. 3A¥. Similarly, the effects of SLCO1B1 and
SLCO1B3 genotypes on the CL/F values of bosentan were not significant ¤Figs. 3B and 3C¥, whereas the mean CL/F value in patients with the SLCO2B1 935AA genotype was marginally higher than that in patients with the 935GG or 935GA genotype ¤Fig. 3D¥. Figure 4 shows the effects of sildenafil, heart failure, and age on the CL/F values of bosentan. Sildenafil, which may interfere with OATP-mediated drug transport,4¥ was concomitantly administered to 15 of 46 patients ¤Table 1¥, but the mean CL/F value of bosentan in patients taking sildenafil was similar to that in patients not taking sildenafil ¤Fig. 4A¥. In addition, 24 patients had severe heart failure with elevation of the serum BNP or NTproBNP concentration, and the mean CL/F value was slightly decreased in patients with severe heart failure ¤Fig. 4B¥. Patient age in the present study ranged from 25 days to 16.9 years ¤Table 1¥, and weight-normalized individual values of CL/F seemed to decrease with increasing age ¤Fig. 4C¥.
Copyright © 2011 by the Japanese Society for the Study of Xenobiotics (JSSX)
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Pharmacokinetics of Bosentan in Japanese Pediatric Patients 1.00
1.00 C
CL/F (L/hr/kg)
CL/F (L/hr/kg)
A
0.75 0.50 0.25 0
0.75 0.50 0.25 0
Group 2
Group 1
Group 1
CYP3A5 genotypes
Group 2
SLCO1B3 genotypes
1.00
1.00 D
CL/F (L/hr/kg)
CL/F (L/hr/kg)
B
0.75 0.50 0.25 0
0.75 0.50 0.25 0 Group 1 Group 2 Group 3
Group 2
Group 1
SLCO1B1 genotypes
SLCO2B1 genotypes
Fig. 3. Effects of CYP3A5/CYP2C9 (A), SLCO1B1 (B), SLCO1B3 (C), and SLCO2B1 (D) genotypes on the CL/F values of bosentan Patients were divided into two or three groups according to their genotypes (see Table 2). Open and closed circles in panel (A) indicate patients with CYP2C9 1075AA genotype and 1075AC genotype, respectively.
1.00
1.00
1.00
0.50 0.25 0
CL/F (L/hr/kg)
0.75
0.75 0.50 0.25
(+)
Sildenafil
BNP <100 NT-proBNP 䚷<400
0.75 0.50 0.25 0
0
(-)
C
B
CL/F (L/hr/kg)
CL/F (L/hr/kg)
A
100< 400<
0
5
10
15
20
AGE (year)
Fig. 4. Effects of sildenafil (A), heart failure (B), and age (C) on the CL/F values of bosentan
Table 3 shows the results of the stepwise forward selection of possible factors ¤variables¥ influencing the pharmacokinetics of bosentan. At Stage 1, we evaluated the effects of possible influencing factors on CL/F and k of bosentan using Models 1®10. The LLD value between the base model and Model 8 was 6.88 ¤p g 0.01¥, which is greater than that between the base model and all other analysis models ¤Models 1®7, 9, and 10¥. These results suggested that age is a significant variable in predicting the CL/F of bosentan. All unselected variables with LLD h 1 were retained as candidates for Stage 2. That is, the effects
of SLCO2B1 genotypes, severe heart failure, and the body weight ¤WT¥ on CL/F were evaluated in Models 11®13; however, no further significant improvement was observed ¤Table 3¥. Thus, Model 8 was selected as the final model to describe the pharmacokinetics of routinely administered bosentan in Japanese pediatric patients. Table 5 summarizes the population pharmacokinetic parameters of bosentan and their 95% CI for the final model. The value of Í10 was estimated to be 0.0377 and the 95% CI values for Í10 did not cover the null value, suggesting that the CL/F of bosentan decreases by 3.77% per
Copyright © 2011 by the Japanese Society for the Study of Xenobiotics (JSSX)
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Masato TAGUCHI, et al.
Table 5. Population pharmacokinetic parameters of bosentan estimated with the final model Parameters
Estimates
95% CI
Í1 ¤L/h/kg¥
0.409
0.340®0.478
Í2 ¤h%1¥
0.175
0.158®0.192
Í10
0.0377
0.0036®0.0718
Ý2CL/F
0.257
0.172®0.342
Ý 2k
0.0895
0.0411®0.1379
The final model was modeled using the following equations ¤Model 8¥: CL/Fi © Í1 & ¤1 % Í10 & ¤AGE % 3.81¥¥ & WTi & exp¤ÌCL=Fi ¥ and ki © Í2 & exp¤Ìki ¥
year in pediatric patients. In addition, the Ý2CL/F value for the final model was smaller than that for the simplest base model ¤Tables 4 and 5¥. Figure 2C shows the relationship between the observed concentrations and the concentrations predicted by the population mean parameters of the final model ¤Table 5¥. The correlation coefficient ¤R¥ for the final model was higher than that for the simplest base model ¤Figs. 2A and 2C¥. Discussion Well-known differences exist in the disposition of drugs between children and adults and between children of different ages.26,27¥ Because well-designed clinical studies in children are scarce, dosing schemes in children are usually derived in an empirical manner from clinical trials in healthy volunteers and/or restricted adult patient groups, and are often based on a linear extrapolation on the basis of body weight.26,28¥ To account for differences in the drug disposition between children of different ages, higher or lower dosages per kilogram body weight are regularly recommended in different age groups.26¥ The age-specific usual doses of drugs ¤e.g. theophylline, phenytoin, phenobarbital, and captopril¥ at least partly result from developmental changes in hepatic clearance.27¥ However, the mechanisms underlying these age-related differences in drug disposition are largely unknown. Barst et al.29¥ investigated the pharmacokinetics of bosentan in 18 pediatric patients. Patients weighing between 10 and 20 kg ¤3.0®8.0 years old¥, between 20 and 40 kg ¤6.0®13.0 years old¥, or greater than 40 kg ¤12.0®15.0 years old¥ received multiple doses of 31.25, 62.5, or 125 mg, respectively, twice daily. The mean CL/F values were estimated to be 0.523, 0.371, and 0.440 L/h/kg in the 3.0® 8.0 year-old, 6.0®13.0 year-old, and 12.0®15.0 year-old groups, respectively. There was no significant effect of age on the pharmacokinetics of the drug.29¥ In contrast, we demonstrated that the CL/F of bosentan changed significantly along with age in our 46 pediatric patients ¤Table 3 and Fig. 4C¥. In our study, 32 of 46 patients were younger than 3 years old. The final population mean value of CL/F was estimated to be 0.409 & ¤1 % 0.0377 & ¤AGE % 3.81¥¥ & WT L/h ¤Table 5¥, indicating that the CL/F value decreased by
3.77% per year. To our knowledge, this is the first report providing information on age-related differences in the pharmacokinetics of bosentan in early childhood in pediatric patients. Treiber et al.4¥ reported that bosentan was a substrate of human OATP1B1, OATP1B3, and OATP2B1 using cultured cell lines stably expressing these OATP proteins. Intrinsic transport capacities expressed as Vmax/Km values for OATP1B1, OATP1B3, and OATP2B1 were 0.023, 0.030, and 0.011 µg/mL&µg protein, respectively.4¥ In the present study, there was no significant effect of SLCO1B1 or SLCO1B3 genotypes on the CL/F of bosentan, whereas the mean CL/F value of the drug was slightly elevated in patients with the SLCO2B1 935AA genotype ¤Fig. 3D¥. Recently, Mougey et al.15¥ reported that SLCO2B1 polymorphisms were associated with significantly reduced plasma concentrations of montelukast in patients with asthma. They thought that the SLCO2B1 935GhA allele could decrease the intestinal absorption of montelukast, because human OATP2B1 is expressed not only on the sinusoidal membrane of the liver but also on the apical membrane of the intestine.15¥ Further systematic studies may be needed to clarify the mechanisms responsible for the intestinal absorption of bosentan. In the present study, we could recruit only 46 pediatric patients at three hospitals. No effect of genetic polymorphisms of CYP3A5, SLCO1B1, SLCO1B3, and SLCO2B1; the coadministration of sildenafil; or heart failure on the pharmacokinetics of bosentan was detected in the present study, although the values of CL/F were correlated negatively with the age of patients. It has been reported that pulmonary arterial hypertension is a relatively rare disease, with an annual incidence of 1®2 cases per 1 million in the general population.30,31¥ Therefore, a further multicenter trial will be necessary to clarify the mechanisms responsible for the large interindividual variability in the pharmacokinetics of bosentan in pediatric patients. In conclusion, we demonstrated considerable individual variability in the plasma concentration of bosentan in routinely treated Japanese pediatric patients; we also found that the CL/F value of bosentan was relatively high in early childhood. Acknowledgements: This work was supported in part by Grants-in-Aid for Scientific Research from the Japan Society for the Promotion of Sciences ¤JSPS¥; from the Ministry of Education, Culture, Sports, Science and Technology of Japan ¤MEXT¥; and the Japan Research Foundation for Clinical Pharmacology. References 1¥ Clozel, M., Breu, V., Gray, G. A., Kalina, B., Löffler, B. M., Burri, K., Cassal, J. M., Hirth, G., Müller, M., Neidhart, W. and Ramuz, H.: Pharmacological characterization of bosentan, a new potent orally active nonpeptide endothelin receptor antagonist.
Copyright © 2011 by the Japanese Society for the Study of Xenobiotics (JSSX)
Pharmacokinetics of Bosentan in Japanese Pediatric Patients
J. Pharmacol. Exp. Ther., 270: 228®235 ¤1994¥. 2¥ Weber, C., Gasser, R. and Hopfgartner, G.: Absorption, excretion, and metabolism of the endothelin receptor antagonist bosentan in healthy male subjects. Drug Metab. Dispos., 27: 810®815 ¤1999¥. 3¥ Dingemanse, J. and Van Giersbergen, P. L.: Clinical pharmacology of bosentan, a dual endothelin receptor antagonist. Clin. Pharmacokinet., 43: 1089®1115 ¤2004¥. 4¥ Treiber, A., Schneiter, R., Häusler, S. and Stieger, B.: Bosentan is a substrate of human OATP1B1 and OATP1B3: inhibition of hepatic uptake as the common mechanism of its interactions with cyclosporin A, rifampicin, and sildenafil. Drug Metab. Dispos., 35: 1400®1407 ¤2007¥. 5¥ Horiuchi, I., Mori, Y. I., Taguchi, M., Ichida, F., Miyawaki, T. and Hashimoto, Y.: Mechanisms responsible for the altered pharmacokinetics of bosentan: analysis utilizing rats with bile duct ligationinduced liver dysfunction. Biopharm. Drug Dispos., 30: 326®333 ¤2009¥. 6¥ Nasu, K., Kubota, T. and Ishizaki, T.: Genetic analysis of CYP2C9 polymorphism in a Japanese population. Pharmacogenetics, 7: 405® 409 ¤1997¥. 7¥ Schwarz, U. I.: Clinical relevance of genetic polymorphisms in the human CYP2C9 gene. Eur. J. Clin. Invest., 33 Suppl. 2: 23®30 ¤2003¥. 8¥ Lamba, J. K., Lin, Y. S., Schuetz, E. G. and Thummel, K. E.: Genetic contribution to variable human CYP3A-mediated metabolism. Adv. Drug Deliv. Rev., 54: 1271®1294 ¤2002¥. 9¥ Hesselink, D. A., van Schaik, R. H., van der Heiden, I. P., van der Werf, M., Gregoor, P. J., Lindemans, J., Weimar, W. and van Gelder, T.: Genetic polymorphisms of the CYP3A4, CYP3A5, and MDR-1 genes and pharmacokinetics of the calcineurin inhibitors cyclosporine and tacrolimus. Clin. Pharmacol. Ther., 74: 245®254 ¤2003¥. 10¥ Lin, Y. S., Dowling, A. L., Quigley, S. D., Farin, F. M., Zhang, J., Lamba, J., Schuetz, E. G. and Thummel, K. E.: Co-regulation of CYP3A4 and CYP3A5 and contribution to hepatic and intestinal midazolam metabolism. Mol. Pharmacol., 62: 162®172 ¤2002¥. 11¥ Fukuen, S., Fukuda, T., Maune, H., Ikenaga, Y., Yamamoto, I., Inaba, T. and Azuma, J.: Novel detection assay by PCR-RFLP and frequency of the CYP3A5 SNPs, CYP3A5*3 and *6, in a Japanese population. Pharmacogenetics, 12: 331®334 ¤2002¥. 12¥ Katz, D. A., Carr, R., Grimm, D. R., Xiong, H., Holley-Shanks, R., Mueller, T., Leake, B., Wang, Q., Han, L., Wang, P. G., Edeki, T., Sahelijo, L., Doan, T., Allen, A., Spear, B. B. and Kim, R. B.: Organic anion transporting polypeptide 1B1 activity classified by SLCO1B1 genotype influences atrasentan pharmacokinetics. Clin. Pharmacol. Ther., 79: 186®196 ¤2006¥. 13¥ Nozawa, T., Nakajima, M., Tamai, I., Noda, K., Nezu, J., Sai, Y., Tsuji, A. and Yokoi, T.: Genetic polymorphisms of human organic anion transporters OATP-C ¤SLC21A6¥ and OATP-B ¤SLC21A9¥: allele frequencies in the Japanese population and functional analysis. J. Pharmacol. Exp. Ther., 302: 804®813 ¤2002¥. 14¥ Tsujimoto, M., Dan, Y., Hirata, S., Ohtani, H. and Sawada, Y.: Influence of SLCO1B3 gene polymorphism on the pharmacokinetics of digoxin in terminal renal failure. Drug Metab. Pharmacokinet., 23: 406®411 ¤2008¥. 15¥ Mougey, E. B., Feng, H., Castro, M., Irvin, C. G. and Lima, J. J.: Absorption of montelukast is transporter mediated: a common variant of OATP2B1 is associated with reduced plasma concentrations and poor response. Pharmacogenet. Genomics, 19: 129®138 ¤2009¥.
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16¥ Tsujimoto, M., Hirata, S., Dan, Y., Ohtani, H. and Sawada, Y.: Polymorphisms and linkage disequilibrium of the OATP8 ¤OATP1B3¥ gene in Japanese subjects. Drug Metab. Pharmacokinet., 21: 165®169 ¤2006¥. 17¥ Pasanen, M. K., Neuvonen, P. J. and Niemi, M.: Global analysis of genetic variation in SLCO1B1. Pharmacogenomics, 9: 19®33 ¤2008¥. 18¥ Beal, S. L., Boeckmann, A. J. and Sheiner, L. B.: NONMEM Users Guides: NONMEM Project Group, San Francisco, University of California, 1992. 19¥ Lee, S. J., Usmani, K. A., Chanas, B., Ghanayem, B., Xi, T., Hodgson, E., Mohrenweiser, H. W. and Goldstein, J. A.: Genetic findings and functional studies of human CYP3A5 single nucleotide polymorphisms in different ethnic groups. Pharmacogenetics, 13: 461®472 ¤2003¥. 20¥ Beghetti, M., Haworth, S. G., Bonnet, D., Barst, R. J., Acar, P., Fraisse, A., Ivy, D. D., Jais, X., Schulze-Neick, I., Galiè, N., Morganti, A., Dingemanse, J., Kusic-Pajic, A. and Berger, R. M.: Pharmacokinetic and clinical profile of a novel formulation of bosentan in children with pulmonary arterial hypertension: the FUTURE-1 study. Br. J. Clin. Pharmacol., 68: 948®955 ¤2009¥. 21¥ Takaai, M., Kayano, Y., Shimizu, T., Taguchi, M. and Hashimoto, Y.: Additional notes on clinical repeated-dose pharmacokinetic trials applying a peak-and-trough sampling design to estimate oral clearance. Drug Metab. Pharmacokinet., 23: 128®133 ¤2008¥. 22¥ Sheiner, L. B. and Beal, S. L.: Evaluation of methods for estimating population pharmacokinetic parameters. III. Monoexponential model: routine clinical pharmacokinetic data. J. Pharmacokinet. Biopharm., 11: 303®319 ¤1983¥. 23¥ Cahalan, M. K., Hashimoto, Y., Aizawa, K., Verotta, D., Ionescu, P., Balea, M., Eger, E. I., 2nd, Benet, L. Z., Ehrenfeld, W. K., Goldstone, J., Reilly, L. M., Stoney, R. J. and Sheiner, L. B.: Elderly, conscious patients have an accentuated hypotensive response to nitroglycerin. Anesthesiology, 77: 646®655 ¤1992¥. 24¥ Honda, M., Ogura, Y., Toyoda, W., Taguchi, M., Nozawa, T., Inoue, H. and Hashimoto, Y.: Multiple regression analysis of pharmacogenetic variability of carvedilol disposition in 54 healthy Japanese volunteers. Biol. Pharm. Bull., 29: 772®778 ¤2006¥. 25¥ Maitre, P. O., Bührer, M., Thomson, D. and Stanski, D. R.: A three-step approach combining Bayesian regression and NONMEM population analysis: application to midazolam. J. Pharmacokinet. Biopharm., 19: 377®384 ¤1991¥. 26¥ Ince, I., de Wildt, S. N., Tibboel, D., Danhof, M. and Knibbe, C. A.: Tailor-made drug treatment for children: creation of an infrastructure for data-sharing and population PK-PD modeling. Drug Discov. Today, 14: 316®320 ¤2009¥. 27¥ Kearns, G. L., Abdel-Rahman, S. M., Alander, S. W., Blowey, D. L., Leeder, J. S. and Kauffman, R. E.: Developmental pharmacology¯drug disposition, action, and therapy in infants and children. N. Engl. J. Med., 349: 1157®1167 ¤2003¥. 28¥ Burns, J. P.: Research in children. Crit. Care Med., 31: S131®S136 ¤2003¥. 29¥ Barst, R. J., Ivy, D., Dingemanse, J., Widlitz, A., Schmitt, K., Doran, A., Bingaman, D., Nguyen, N., Gaitonde, M. and Van Giersbergen, P. L.: Pharmacokinetics, safety, and efficacy of bosentan in pediatric patients with pulmonary arterial hypertension. Clin. Pharmacol. Ther., 73: 372®382 ¤2003¥. 30¥ Shintani, M., Yagi, H., Nakayama, T., Saji, T. and Matsuoka, R.: A new nonsense mutation of SMAD8 associated with pulmonary arterial hypertension. J. Med. Genet., 46: 331®337 ¤2009¥. 31¥ Farber, H. W. and Loscalzo, J.: Pulmonary arterial hypertension. N. Engl. J. Med., 351: 1655®1665 ¤2004¥.
Copyright © 2011 by the Japanese Society for the Study of Xenobiotics (JSSX)
Copyright © 2011 by the Japanese Society for the Study of Xenobiotics (JSSX)
Regular Article Pharmacokinetics of Bosentan in Routinely Treated Japanese Pediatric Patients with Pulmonary Arterial Hypertension Masato TAGUCHI 1 , Fukiko I CHIDA 1 , Keiichi H IRONO 1 , Toshio M IYAWAKI 1 , Naoki YOSHIMURA 1 , Tsuneyuki N AKAMURA 2, Chisato A KITA 2, Tomotaka N AKAYAMA 3 , Tsutomu S AJI 3 , Yuya K ATO 1 , Isao H ORIUCHI 1 and Yukiya H ASHIMOTO 1, * 1 Graduate
School of Medicine and Pharmaceutical Sciences, University of Toyama, Toyama, Japan 2 Department of Pediatrics, Kanazawa Medical University, Kahoku, Japan 3 Department of Pediatrics, Faculty of Medicine, Toho University Medical Center, Omori Hospital, Tokyo, Japan
Full text of this paper is available at http://www.jstage.jst.go.jp/browse/dmpk Summary: We evaluated the pharmacokinetics of routinely administered bosentan in 46 Japanese pediatric patients with pulmonary arterial hypertension. Plasma samples were taken twice at times corresponding to the peak and trough concentrations following repetitive oral administration. The population pharmacokinetic parameters of bosentan were estimated by use of the NONMEM program, in which a onecompartment model with repetitive bolus dosing was parameterized in terms of the oral clearance (CL/F) and elimination rate constant (k). Polymorphisms of CYP3A5, SLCO1B1, SLCO1B3, and SLCO2B1 had no significant effect on the disposition of bosentan. In addition, the pharmacokinetics of bosentan was not altered by heart failure or coadministration of sildenafil. In contrast, weight (WT)-normalized values of CL/F were correlated negatively with age (AGE). The final population mean values of CL/F and k were estimated to be 0.409 · (1 ¹ 0.0377 · (AGE ¹ 3.81)) · WT L/h and 0.175 h ¹1 , respectively. Keywords: bosentan; pharmacokinetics; pediatric patients; pulmonary arterial hypertension; genetic polymorphisms; organic anion transporting polypeptide; cytochrome P450
of bosentan with cyclosporine, a potent inhibitor of OATPs, is contraindicated owing to risk of greatly increased bosentan levels.3¥ In addition, we have previously demonstrated that OATP substrates ¤taurocholic acid or bilirubin¥ significantly attenuate the hepatic clearance of bosentan in rats.5¥ The genetic polymorphisms of CYP2C9 have been extensively studied, and CYP2C9*1 ¤wild-type¥ and CYP2C9*3 were identified in a Japanese population.6¥ CYP2C9*3 ¤1075AhC¥ is an allelic variant in exon 7 that produces an enzyme with an Ile359/Leu359 amino acid substitution, leading to an impairment in the enzymatic activity of CYP2C9.7¥ The allele frequency of CYP2C9*3 among the Japanese is reported to be only 2.1%.6¥ In contrast, more than 30 single nucleotide polymorphisms ¤SNPs¥ have been identified in the CYP3A4 gene.8¥ For the most common variant, CYP3A4*1B, increased transcription was demonstrated in vitro, which may theoretically result in greater enzymatic activity in vivo.9¥ However, the allele
Introduction Bosentan is a potent nonpeptidic endothelin receptor antagonist with high affinity for both endothelin A and B receptors; it is usually administered orally twice a day to patients with pulmonary arterial hypertension.1¥ Bosentan is eliminated predominantly by hepatic metabolism, with renal excretion accounting for only 0.9% of the administered dose.2¥ After single intravenous administration of bosentan at a dose of 250 mg to healthy male subjects, the amounts of hydroxy-, phenolic-, and hydroxy-phenolic metabolites excreted into feces within 5 days were 47.5%, 6.4%, and 17.7% of the dose, respectively.2¥ The formation of these major bosentan metabolites is catalyzed by cytochrome P450 ¤CYP¥ 2C9 and CYP3A4 in the human liver.3¥ On the other hand, Treiber et al.4¥ reported that bosentan is a substrate of human organic anion transporting polypeptide ¤OATP¥ 1B1, OATP1B3, and OATP2B1, which are expressed on the sinusoidal membrane in the human liver. Coadministration
Received; November 7, 2010, Accepted; February 8, 2011 J-STAGE Advance Published Date: March 4, 2011, doi:10.2133/dmpk.DMPK-10-RG-113 *To whom correspondence should be addressed: Yukiya HASHIMOTO, Ph.D., Graduate School of Medicine and Pharmaceutical Sciences, University of Toyama, 2630 Sugitani, Toyama 930-0194, Japan. Tel. +81-76-434-7585, Fax. +81-76-434-7586, E-mail: [email protected] 280
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Pharmacokinetics of Bosentan in Japanese Pediatric Patients
frequency of CYP3A4*1B was found to be extremely low in the Japanese.8¥ CYP3A5 is another important CYP3A protein in the liver and exhibits significant overlap with CYP3A4 in substrate specificity.10¥ The defective allelic variant, CYP3A5*3 ¤6986AhG¥, was frequently observed in a Japanese population.11¥ Several sequence variations and their haplotypes have been discovered in the solute carrier organic anion transporter ¤SLCO¥ 1B1, SLCO1B3, and SLCO2B1 genes encoding OATP1B1, OATP1B3, and OATP2B1, respectively.12®17¥ It has been reported that the SLCO1B1 521ThC allele is associated with increased plasma concentration of the endothelin I receptor antagonist atrasentan.12¥ That is, the geometric mean for the area under the plasma concentration®time curve during a dose interval ¤AUCØ¥ of atrasentan in patients with the SLCO1B1 521TC genotype was 14% higher than that in patients with the 521TT genotype.12¥ The allele frequency of SLCO1B1 521ThC among Japanese was reported to be 11.0%.13¥ Recently, it was also reported that the genotype of SLCO1B3 and SLCO2B1 affected the pharmacokinetics of digoxin and montelukast, respectively.14,15¥ The main purpose of the present study was to evaluate the pharmacokinetics of bosentan in Japanese pediatric patients and to investigate the effects of CYP3A5, SLCO1B1, SLCO1B3, and SLCO2B1 ¤and, if possible, CYP2C9¥ genotypes on the pharmacokinetics of bosentan. Pharmacokinetic analysis was performed using a nonlinear mixedeffects model ¤NONMEM¥ program, because population pharmacokinetics based on NONMEM analysis can simultaneously evaluate the mean pharmacokinetic parameters, the covariates affecting the pharmacokinetics of a drug, and also unknown inter- and intra-individual pharmacokinetic variability.18¥ Methods Subjects and study protocols: Forty-six Japanese pediatric patients with pulmonary arterial hypertension ¤29 boys and 17 girls¥ participated in this study, and their demographic and clinical data are summarized in Table 1. The patients ranged in age from 25 days to 16.9 years old, and in body weight from 3.5 to 57.0 kg. In addition, 26 patients had undergone cardiac surgery and 10 patients were characterized as having Downös syndrome. Although no patients had severe hepatic or renal failure, 24 patients had severe chronic heart failure. That is, the N-terminal probrain natriuretic peptide ¤NT-proBNP¥ concentration was above 400 pg/mL ¤normal range: 0®125 pg/ml¥ in 15 of 20 patients, and the brain natriuretic peptide ¤BNP¥ concentration was above 100 pg/mL ¤normal range: 0®18.4 pg/mL¥ in 9 of 26 patients. The patients were routinely treated with oral administration of bosentan hydrate ¤Tracleer tablet, Actelion Pharmaceuticals, Tokyo, Japan¥. Bosentan was administered twice a day to 45 patients and three times a day to 1 patient. The dose of bosentan was
Table 1. Demographics of 46 Japanese pediatric patients with pulmonary arterial hypertension Age ¤year¥
3.81 + 4.79 ¤25 days to 16.9 years¥
Body weight ¤kg¥
13.4 + 12.6 ¤3.5®57.0¥
Sex Number of males
29 patients
Number of females
17 patients
Bosentan dose ¤mg/kg/day¥
2.34 + 0.80 ¤0.49®4.78¥
Blood sampling time after dose ¤h¥ Peak
3.1 + 0.3 ¤2.8®4.0¥
Trough
12.9 + 2.2 ¤8.0®17.3¥
Natriuretic peptides ¤pg/mL¥ NT-proBNP ¤n © 20¥
1509 + 3646 ¤119®16855¥
BNP ¤n © 26¥
112 + 161 ¤ND* to 762¥
Concomitant drug Furosemide
40 patients
Spironolactone
39 patients
Beraprost
30 patients
Aspirin
23 patients
Enalapril
21 patients
Warfarin
20 patients
Sildenafil
15 patients
Digoxin
10 patients
Carvedilol
6 patients
Values are expressed as mean + S.D. ¤range¥ unless specified otherwise. *ND: not detected.
based solely on clinical considerations, and the mean daily dose was 2.34 + 0.80 mg/day/kg. Most patients took multiple drugs concomitantly with bosentan, but no patients had concomitant medication known to potently inhibit CYP2C9, CYP3A4/5, or OATP activity ¤e.g. amiodarone, ketoconazole, or cyclosporine¥. Two blood samples ªjust before the dose, corresponding to trough concentrations ¤Ctrough¥, and at 2.8®4.0 h after the dose, corresponding to peak concentrations ¤Cpeak¥« were withdrawn from each patient at steady state following repetitive dosing for more than 4 weeks ¤Table 1¥. Blood sampling was performed on the same day ¤in 21 outpatients and 14 inpatients¥ or on different days ¤in 11 outpatients¥. The patients and/or their family members gave written informed consent to participate in this study, which was approved by the ethics committee of the University of Toyama ¤#EG19-3¥. Genotyping of drug metabolizing enzymes and transporters: Genomic DNA was isolated from the peripheral blood with an extraction kit ¤QIAGEN, Hilden, Germany¥. Polymorphisms of CYP2C9 ¤1075AhC; rs1057910¥ and SLCO1B3 ¤334ThG; rs4149117¥ were determined by the polymerase chain reaction-restriction fragment length polymorphism ¤PCR-RFLP¥ method as described previously.6,16¥ A polymorphism of SLCO1B1 ¤521ThC; rs4149056¥ was detected by using the allele-
Copyright © 2011 by the Japanese Society for the Study of Xenobiotics (JSSX)
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Masato TAGUCHI, et al.
Table 2. Genotypes of CYP2C9, CYP3A5, SLCO1B3, and SLCO2B1 in 46 patients Gene
SNP
Location
CYP2C9
1075AhC
Exon 7
CYP3A5
6986AhG Intron 3
rs #
SLCO1B1,
CL=Fi ¼ Í 1 WTi expðÌCL=Fi Þ
Genotype Group 1
Group 2
Group 3
rs1057910 A/A ¤45¥ A/C ¤1¥ rs776746
A/A ¤2¥ G/G ¤27¥ A/G ¤17¥
SLCO1B1
521ThC
Exon 5
rs4149056 T/T ¤38¥
SLCO1B3
334ThG
Exon 3
rs4149117
T/C ¤8¥
T/T ¤1¥ G/G ¤26¥ T/G ¤19¥
SLCO2B1
935GhA
Exon 7
rs12422149 G/G ¤23¥ G/A ¤15¥ A/A ¤8¥
Figures shown in parentheses indicate the number of patients.
specific PCR amplification method.13¥ In contrast, polymorphisms of CYP3A5 ¤6986AhG; rs776746¥ and SLCO2B1 ¤935GhA; rs12422149¥ were determined by direct sequencing.15,19¥ In the present study, the patients were divided into two or three groups according to the genotypes of each drug metabolizing enzyme or transporter ¤Table 2¥. Assay of bosentan: Plasma concentrations of bosentan were determined by a reversed-phase HPLC method.5¥ The HPLC system consisted of an LC-10Avp Liquid Chromatograph Series ¤Shimadzu, Kyoto, Japan¥ with a model SPD-10Avp UV-visible detector ¤Shimadzu¥ and the Inertsil ODS-3 column ¤15 cm ' 4.6 mm i.d.; 3 µm particle size; GL Sciences, Tokyo, Japan¥. The mobile phase was acetonitrile and 5 mM CH3COONH4 adjusted to pH 2.69 with acetic acid ¤41/59, v/v¥. A 0.3-mL aliquot of plasma samples was acidified with 1.2 mL of 1 M citrate buffer ¤pH 4.0¥, and mildly extracted with 5 mL of a mixture of nbutyl chloride and dichloromethane ¤4/1, v/v¥. The organic phase was then evaporated to dryness with a SpeedVac system ¤Savant, Famingdale, NY, U.S.A.¥. The residue was dissolved in 200 µL of mobile phase, and 150 µL was injected into the column. The flow rate of the mobile phase was 1.0 mL/min, and the column temperature was 40ôC. Peaks were monitored at 270 nm, and the retention time was 24 min for bosentan. The quantitation limit for bosentan was a plasma concentration of 5 ng/mL. In addition, the coefficient of intra-day variation of this assay was 3.8% and 2.5% at plasma bosentan concentrations of 200 and 2000 ng/mL, respectively. Population pharmacokinetic analysis: The time required to reach the peak concentration after oral administration of a conventional preparation of bosentan is short ¤median: 3.0 h¥.20¥ In the present study, no plasma concentration data of bosentan was obtained at the absorption phase ¤0®2.8 h after oral administration¥. Therefore, the one-compartment model with repetitive bolus dosing was parameterized in terms of the oral clearance ¤CL/F¥ and the elimination rate constant ¤k¥.21¥ For the simplest base model, the oral clearance in the ith individual ¤CL/Fi¥ was modeled using the following equation:
ð1Þ
where WTi is the individual body weight ¤in kg¥, Í1 & WTi is the predicted population mean of CL/F ¤in L/h¥, and ÌCL=Fi is a random variable distributed normally with a mean of zero and variance of Ý2CL/F. The elimination rate constant in the ith individual ¤ki¥ was modeled using the following equation: ki ¼ Í2 expðÌki Þ
ð2Þ %1
where Í2 is a predicted population mean of k ¤in h ¥, and Ìki is a random variable distributed normally with a mean of zero and variance of Ý2k. Finally, the jth observed plasma concentration in the ith patient ¤Cpij¥ was assumed to be randomly distributed from the jth predicted plasma concentration in the ith patient ¤Cpij ¥: Cpij ¼ Cpij expðÞij Þ
ð3Þ
where Þij is a random variable that describes intraindividual variability with a mean of zero and variance of Ö2. In the present study, the number of blood samplings was only two in each patient, and the Ö2 value was frequently unobtainable. Therefore, the Ö2 value was fixed to 0.0225 ¤i.e., 0.152¥ throughout the study.22¥ We further performed the stepwise forward selection of possible factors ¤variables¥ influencing the pharmacokinetics of bosentan.23,24¥ Table 3 summarizes the 10 analysis models at Stage 1 of the selection. The effect of CYP2C9 genotypes on the CL/F of bosentan was evaluated with Model 1, where G2CYP2C9 © 0 for Group 1 patients with the CYP2C9 1075AA genotype and G2CYP2C9 © 1 for Group 2 patients with the 1075AC genotype. The effect of CYP3A5 genotypes on the CL/F of bosentan was evaluated with Model 2, where G1CYP3A5 © 1 for Group 1 patients with the CYP3A5 6986AA or 6986AG genotype and G1CYP3A5 © 0 for Group 2 patients with the 6986GG genotype. The effect of SLCO1B1 genotypes on CL/F was evaluated with Model 3, where G2SLCO1B1 © 0 for Group 1 patients with the SLCO1B1 521TT genotype and G2SLCO1B1 © 1 for Group 2 patients with the 521TC genotype. The effect of SLCO1B3 genotypes on CL/F was evaluated with Model 4, where G2SLCO1B3 © 0 for Group 1 patients with the SLCO1B3 334TT or 334TG genotype and G2SLCO1B3 © 1 for Group 2 patients with the 334GG genotype. The effect of SLCO2B1 genotypes on CL/F was evaluated with Model 5, where G2SLCO2B1 © 0 and G3SLCO2B1 © 0 for Group 1 patients with the SLCO2B1 935GG genotype, G2SLCO2B1 © 1 and G3SLCO2B1 © 0 for Group 2 patients with the 935GA genotype, and G2SLCO2B1 © 0 and G3SLCO2B1 © 1 for Group 3 patients with the 935AA genotype ¤Table 3¥. The effect of coadministration of sildenafil on CL/F was evaluated using Model 6, where Sildenafil is one for patients taking sildenafil and zero for the other patients. The effect of heart failure on CL/F was evaluated using Model 7, where BNP h100 is one for patients with severe chronic heart failure ¤in which the BNP or NT-proBNP
Copyright © 2011 by the Japanese Society for the Study of Xenobiotics (JSSX)
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Pharmacokinetics of Bosentan in Japanese Pediatric Patients Table 3. Stepwise forward selection of variables for the oral clearance and elimination rate constant Stage
Model
1
1
CYP2C9 CL=Fi ¼ Í 1 Í G2 WTi expðÌCL=Fi Þ 3
0.06 vs. base model
2
CYP3A5 WTi expðÌCL=Fi Þ CL=Fi ¼ Í 1 Í G1 4
0.04 vs. base model
3
SLCO1B1 WTi expðÌCL=Fi Þ CL=Fi ¼ Í 1 Í G2 5
0.09 vs. base model
4
SLCO1B3 WTi expðÌCL=Fi Þ CL=Fi ¼ Í 1 Í G2 6
0.22 vs. base model
5
CL=Fi ¼ ðÍ 1 þ Í 7 G2SLCO2B1 þ 2 Í 7 G3SLCO2B1 Þ WTi expðÌCL=Fi Þ
3.30~ vs. base model
6
CL=Fi ¼ Í 1 Í Sildenafil WTi expðÌCL=Fi Þ 8
0.07 vs. base model
7
WTi expðÌCL=Fi Þ CL=Fi ¼ Í 1 Í BNP>100 9
8 9 10 2
Formula
LLD
2.17~ vs. base model
CL=Fi ¼ Í 1 ð1
Í 10 ðAGE 3:81ÞÞ WTi expðÌCL=Fi Þ WTi Í11 CL=Fi ¼ Í 1 13:4 expðÌki Þ 13:4 Í12 WTi ki ¼ Í 2 expðÌki Þ 13:4
¡
11
CL=Fi ¼ ðÍ 1 þ Í 7 G2SLCO2B1 þ 2 Í 7 G3SLCO2B1 Þ ð1
12
CL=Fi ¼ Í 1 Í BNP>100 ð1 Í 10 ðAGE 3:81ÞÞ WTi expðÌCL=Fi Þ 9 WTi Í11 CL=Fi ¼ Í 1 13:4 ð1 Í 10 ðAGE 3:81ÞÞ expðÌki Þ 13:4
13
Í 10 ðAGE
6.88* vs. base model 4.38~ vs. base model 0.29 vs. base model 3:81ÞÞ WTi expðÌCL=Fi Þ
4.30 vs. Model 8 1.45 vs. Model 8 1.21 vs. Model 8
*p g 0.01 compared with base model. ~Unselected variables with LLD decreases of h1 at Stage 1 were retained as candidates for selection at Stage 2. ¡The model selected as the final model.
concentration was higher than 100 pg/mL or 400 pg/mL, respectively¥ and zero for the other patients. The effect of age on CL/F was evaluated using Model 8. In addition, the effects of body weight on CL/F and k were evaluated using Models 9 and 10, respectively ¤Table 3¥. Data analysis was performed with the NONMEM software ¤double-precision NONMEM Version V Level 1.1, PREDPP Version IV Level 1.1, and NM-TRAN Version III Level 1.1¥18¥ running on a mainframe UNIX supercomputer at the Kyoto University Academic Center for Computing and Media Studies. In the present study, we used a first-order conditional estimation method and the NONMEM-PREDPP library subroutines ADVAN1 and TRANS1 for the one-compartment model with bolus dosing.18¥ The statistical significance of the model parameter was evaluated with the likelihood ratio test using the minimum value of the objective function ¤%2 log likelihood¥ produced by NONMEM.18,24¥ In the present study, when the %2 log likelihood difference ¤LLD¥ between two models allowing a parameter of interest to be freely estimated versus a fixed hypothetical value was greater than 6.63, the parameter value was considered to be statistically significant ¤p g 0.01¥. In addition, NONMEM provides estimates of the standard error ¤S.E.¥ for all parameters, and S.E. can be used to define 95% confidence intervals ¤CI¥ for true parameter values: 95% CI © ¤the estimated parameter value¥ + 1.96 & S.E.18,24¥ Results The genotypes of CYP2C9, CYP3A5, SLCO1B1, SLCO1B3, and SLCO2B1 in the 46 Japanese pediatric patients are
shown in Table 2. Figure 1 shows the plasma concentrations of bosentan in individual patients. A more than 50-fold difference was observed between the highest and lowest peak concentrations ¤Fig. 1A¥. On the other hand, a large interindividual difference was still observed when the plasma concentrations were corrected for the daily dose of the drug ¤Fig. 1B¥. Table 4 shows the population mean pharmacokinetic parameters of bosentan that were estimated by using the simplest base model. The Í1 and Í2 values were estimated to be 0.401 L/h/kg and 0.175 h%1, respectively. The Ý2CL/F and Ý2k values were estimated to be 0.304 and 0.0868, respectively, indicating the especially large interindividual variation of CL/F ¤Table 4¥. Figure 2A shows the relationship between the observed bosentan plasma concentrations and the respective concentrations predicted by the population mean parameters of the base model. Although the correlation between the observed and predicted concentrations was not very high, the observed concentrations seemed to be distributed randomly from the predicted concentrations. To explore factors influencing the pharmacokinetics of bosentan, the pharmacokinetic parameters in individual patients were estimated by the Bayesian method using a posthoc option of the NONMEM program.18,25¥ Figure 2B shows the relationship between the observed bosentan plasma concentrations and the respective concentrations estimated by Bayesian analysis with population parameters of the base model. The improved correlation in Figure 2B suggested that the pharmacokinetic parameters in individual patients were well estimated by Bayesian analysis. Figure 3 shows the effects of CYP2C9, CYP3A5, SLCO1B1,
Copyright © 2011 by the Japanese Society for the Study of Xenobiotics (JSSX)
284
10000
Plasma conc. (ng/mL)
A 3000 1000 300 100 30 10 3
0
6
12
18
Plasma conc./Dose (kg䡡day/L)
Masato TAGUCHI, et al.
3 B 1 0.3 0.1 0.03 0.01 0.003 0.001
6
0
Time after dose (hr)
12
18
Time after dose (hr)
Fig. 1. Measured peak and trough plasma concentrations (A) and dose-corrected peak and trough plasma concentrations (B) following repetitive oral administration of bosentan
10
1 0.1 0.01 R=0.843
0.001 0.001
0.01
0.1
1
10
10 B
Observed conc. (ng/mL)
A
Observed conc. (ng/mL)
Observed conc. (ng/mL)
10
1 0.1 0.01 R=0.995
0.001 0.001
Predicted conc. (ng/mL)
0.01
0.1
1
Predicted conc. (ng/mL)
10
C
1 0.1 0.01 R=0.886
0.001 0.001
0.01
0.1
1
10
Predicted conc. (ng/mL)
Fig. 2. The relationship between the observed and predicted bosentan concentrations in 46 patients Concentrations predicted using the population mean parameters of the base model (A), using Bayesian analysis with population parameters of the base model (B), and using the population mean parameters of the final model (C)
Table 4. Population pharmacokinetic parameters of bosentan estimated with the base model Parameters
Estimates
95% CI
Í1 ¤L/h/kg¥
0.401
0.333®0.469
Í2 ¤h%1¥
0.175
0.158®0.192
Ý2CL/F
0.304
0.138®0.470
Ý 2k
0.0868
0.0433®0.1303
The simplest base model was modeled using the following equations: CL/Fi © Í1 & WTi & exp¤ÌCL=Fi ¥ and ki © Í2 & exp¤Ìki ¥
SLCO1B3, and SLCO2B1 genotypes on the individual CL/F values of bosentan. The CL/F value in the patient with the CYP2C9 1075AC genotype was estimated to be 0.412 L/ h/kg, which is similar to the population mean parameter, Í1, for the base model ¤Fig. 3A and Table 4¥. CYP3A5 genotypes seemed to have no effect on the CL/F values of bosentan ¤Fig. 3A¥. Similarly, the effects of SLCO1B1 and
SLCO1B3 genotypes on the CL/F values of bosentan were not significant ¤Figs. 3B and 3C¥, whereas the mean CL/F value in patients with the SLCO2B1 935AA genotype was marginally higher than that in patients with the 935GG or 935GA genotype ¤Fig. 3D¥. Figure 4 shows the effects of sildenafil, heart failure, and age on the CL/F values of bosentan. Sildenafil, which may interfere with OATP-mediated drug transport,4¥ was concomitantly administered to 15 of 46 patients ¤Table 1¥, but the mean CL/F value of bosentan in patients taking sildenafil was similar to that in patients not taking sildenafil ¤Fig. 4A¥. In addition, 24 patients had severe heart failure with elevation of the serum BNP or NTproBNP concentration, and the mean CL/F value was slightly decreased in patients with severe heart failure ¤Fig. 4B¥. Patient age in the present study ranged from 25 days to 16.9 years ¤Table 1¥, and weight-normalized individual values of CL/F seemed to decrease with increasing age ¤Fig. 4C¥.
Copyright © 2011 by the Japanese Society for the Study of Xenobiotics (JSSX)
285
Pharmacokinetics of Bosentan in Japanese Pediatric Patients 1.00
1.00 C
CL/F (L/hr/kg)
CL/F (L/hr/kg)
A
0.75 0.50 0.25 0
0.75 0.50 0.25 0
Group 2
Group 1
Group 1
CYP3A5 genotypes
Group 2
SLCO1B3 genotypes
1.00
1.00 D
CL/F (L/hr/kg)
CL/F (L/hr/kg)
B
0.75 0.50 0.25 0
0.75 0.50 0.25 0 Group 1 Group 2 Group 3
Group 2
Group 1
SLCO1B1 genotypes
SLCO2B1 genotypes
Fig. 3. Effects of CYP3A5/CYP2C9 (A), SLCO1B1 (B), SLCO1B3 (C), and SLCO2B1 (D) genotypes on the CL/F values of bosentan Patients were divided into two or three groups according to their genotypes (see Table 2). Open and closed circles in panel (A) indicate patients with CYP2C9 1075AA genotype and 1075AC genotype, respectively.
1.00
1.00
1.00
0.50 0.25 0
CL/F (L/hr/kg)
0.75
0.75 0.50 0.25
(+)
Sildenafil
BNP <100 NT-proBNP 䚷<400
0.75 0.50 0.25 0
0
(-)
C
B
CL/F (L/hr/kg)
CL/F (L/hr/kg)
A
100< 400<
0
5
10
15
20
AGE (year)
Fig. 4. Effects of sildenafil (A), heart failure (B), and age (C) on the CL/F values of bosentan
Table 3 shows the results of the stepwise forward selection of possible factors ¤variables¥ influencing the pharmacokinetics of bosentan. At Stage 1, we evaluated the effects of possible influencing factors on CL/F and k of bosentan using Models 1®10. The LLD value between the base model and Model 8 was 6.88 ¤p g 0.01¥, which is greater than that between the base model and all other analysis models ¤Models 1®7, 9, and 10¥. These results suggested that age is a significant variable in predicting the CL/F of bosentan. All unselected variables with LLD h 1 were retained as candidates for Stage 2. That is, the effects
of SLCO2B1 genotypes, severe heart failure, and the body weight ¤WT¥ on CL/F were evaluated in Models 11®13; however, no further significant improvement was observed ¤Table 3¥. Thus, Model 8 was selected as the final model to describe the pharmacokinetics of routinely administered bosentan in Japanese pediatric patients. Table 5 summarizes the population pharmacokinetic parameters of bosentan and their 95% CI for the final model. The value of Í10 was estimated to be 0.0377 and the 95% CI values for Í10 did not cover the null value, suggesting that the CL/F of bosentan decreases by 3.77% per
Copyright © 2011 by the Japanese Society for the Study of Xenobiotics (JSSX)
286
Masato TAGUCHI, et al.
Table 5. Population pharmacokinetic parameters of bosentan estimated with the final model Parameters
Estimates
95% CI
Í1 ¤L/h/kg¥
0.409
0.340®0.478
Í2 ¤h%1¥
0.175
0.158®0.192
Í10
0.0377
0.0036®0.0718
Ý2CL/F
0.257
0.172®0.342
Ý 2k
0.0895
0.0411®0.1379
The final model was modeled using the following equations ¤Model 8¥: CL/Fi © Í1 & ¤1 % Í10 & ¤AGE % 3.81¥¥ & WTi & exp¤ÌCL=Fi ¥ and ki © Í2 & exp¤Ìki ¥
year in pediatric patients. In addition, the Ý2CL/F value for the final model was smaller than that for the simplest base model ¤Tables 4 and 5¥. Figure 2C shows the relationship between the observed concentrations and the concentrations predicted by the population mean parameters of the final model ¤Table 5¥. The correlation coefficient ¤R¥ for the final model was higher than that for the simplest base model ¤Figs. 2A and 2C¥. Discussion Well-known differences exist in the disposition of drugs between children and adults and between children of different ages.26,27¥ Because well-designed clinical studies in children are scarce, dosing schemes in children are usually derived in an empirical manner from clinical trials in healthy volunteers and/or restricted adult patient groups, and are often based on a linear extrapolation on the basis of body weight.26,28¥ To account for differences in the drug disposition between children of different ages, higher or lower dosages per kilogram body weight are regularly recommended in different age groups.26¥ The age-specific usual doses of drugs ¤e.g. theophylline, phenytoin, phenobarbital, and captopril¥ at least partly result from developmental changes in hepatic clearance.27¥ However, the mechanisms underlying these age-related differences in drug disposition are largely unknown. Barst et al.29¥ investigated the pharmacokinetics of bosentan in 18 pediatric patients. Patients weighing between 10 and 20 kg ¤3.0®8.0 years old¥, between 20 and 40 kg ¤6.0®13.0 years old¥, or greater than 40 kg ¤12.0®15.0 years old¥ received multiple doses of 31.25, 62.5, or 125 mg, respectively, twice daily. The mean CL/F values were estimated to be 0.523, 0.371, and 0.440 L/h/kg in the 3.0® 8.0 year-old, 6.0®13.0 year-old, and 12.0®15.0 year-old groups, respectively. There was no significant effect of age on the pharmacokinetics of the drug.29¥ In contrast, we demonstrated that the CL/F of bosentan changed significantly along with age in our 46 pediatric patients ¤Table 3 and Fig. 4C¥. In our study, 32 of 46 patients were younger than 3 years old. The final population mean value of CL/F was estimated to be 0.409 & ¤1 % 0.0377 & ¤AGE % 3.81¥¥ & WT L/h ¤Table 5¥, indicating that the CL/F value decreased by
3.77% per year. To our knowledge, this is the first report providing information on age-related differences in the pharmacokinetics of bosentan in early childhood in pediatric patients. Treiber et al.4¥ reported that bosentan was a substrate of human OATP1B1, OATP1B3, and OATP2B1 using cultured cell lines stably expressing these OATP proteins. Intrinsic transport capacities expressed as Vmax/Km values for OATP1B1, OATP1B3, and OATP2B1 were 0.023, 0.030, and 0.011 µg/mL&µg protein, respectively.4¥ In the present study, there was no significant effect of SLCO1B1 or SLCO1B3 genotypes on the CL/F of bosentan, whereas the mean CL/F value of the drug was slightly elevated in patients with the SLCO2B1 935AA genotype ¤Fig. 3D¥. Recently, Mougey et al.15¥ reported that SLCO2B1 polymorphisms were associated with significantly reduced plasma concentrations of montelukast in patients with asthma. They thought that the SLCO2B1 935GhA allele could decrease the intestinal absorption of montelukast, because human OATP2B1 is expressed not only on the sinusoidal membrane of the liver but also on the apical membrane of the intestine.15¥ Further systematic studies may be needed to clarify the mechanisms responsible for the intestinal absorption of bosentan. In the present study, we could recruit only 46 pediatric patients at three hospitals. No effect of genetic polymorphisms of CYP3A5, SLCO1B1, SLCO1B3, and SLCO2B1; the coadministration of sildenafil; or heart failure on the pharmacokinetics of bosentan was detected in the present study, although the values of CL/F were correlated negatively with the age of patients. It has been reported that pulmonary arterial hypertension is a relatively rare disease, with an annual incidence of 1®2 cases per 1 million in the general population.30,31¥ Therefore, a further multicenter trial will be necessary to clarify the mechanisms responsible for the large interindividual variability in the pharmacokinetics of bosentan in pediatric patients. In conclusion, we demonstrated considerable individual variability in the plasma concentration of bosentan in routinely treated Japanese pediatric patients; we also found that the CL/F value of bosentan was relatively high in early childhood. Acknowledgements: This work was supported in part by Grants-in-Aid for Scientific Research from the Japan Society for the Promotion of Sciences ¤JSPS¥; from the Ministry of Education, Culture, Sports, Science and Technology of Japan ¤MEXT¥; and the Japan Research Foundation for Clinical Pharmacology. References 1¥ Clozel, M., Breu, V., Gray, G. A., Kalina, B., Löffler, B. M., Burri, K., Cassal, J. M., Hirth, G., Müller, M., Neidhart, W. and Ramuz, H.: Pharmacological characterization of bosentan, a new potent orally active nonpeptide endothelin receptor antagonist.
Copyright © 2011 by the Japanese Society for the Study of Xenobiotics (JSSX)
Pharmacokinetics of Bosentan in Japanese Pediatric Patients
J. Pharmacol. Exp. Ther., 270: 228®235 ¤1994¥. 2¥ Weber, C., Gasser, R. and Hopfgartner, G.: Absorption, excretion, and metabolism of the endothelin receptor antagonist bosentan in healthy male subjects. Drug Metab. Dispos., 27: 810®815 ¤1999¥. 3¥ Dingemanse, J. and Van Giersbergen, P. L.: Clinical pharmacology of bosentan, a dual endothelin receptor antagonist. Clin. Pharmacokinet., 43: 1089®1115 ¤2004¥. 4¥ Treiber, A., Schneiter, R., Häusler, S. and Stieger, B.: Bosentan is a substrate of human OATP1B1 and OATP1B3: inhibition of hepatic uptake as the common mechanism of its interactions with cyclosporin A, rifampicin, and sildenafil. Drug Metab. Dispos., 35: 1400®1407 ¤2007¥. 5¥ Horiuchi, I., Mori, Y. I., Taguchi, M., Ichida, F., Miyawaki, T. and Hashimoto, Y.: Mechanisms responsible for the altered pharmacokinetics of bosentan: analysis utilizing rats with bile duct ligationinduced liver dysfunction. Biopharm. Drug Dispos., 30: 326®333 ¤2009¥. 6¥ Nasu, K., Kubota, T. and Ishizaki, T.: Genetic analysis of CYP2C9 polymorphism in a Japanese population. Pharmacogenetics, 7: 405® 409 ¤1997¥. 7¥ Schwarz, U. I.: Clinical relevance of genetic polymorphisms in the human CYP2C9 gene. Eur. J. Clin. Invest., 33 Suppl. 2: 23®30 ¤2003¥. 8¥ Lamba, J. K., Lin, Y. S., Schuetz, E. G. and Thummel, K. E.: Genetic contribution to variable human CYP3A-mediated metabolism. Adv. Drug Deliv. Rev., 54: 1271®1294 ¤2002¥. 9¥ Hesselink, D. A., van Schaik, R. H., van der Heiden, I. P., van der Werf, M., Gregoor, P. J., Lindemans, J., Weimar, W. and van Gelder, T.: Genetic polymorphisms of the CYP3A4, CYP3A5, and MDR-1 genes and pharmacokinetics of the calcineurin inhibitors cyclosporine and tacrolimus. Clin. Pharmacol. Ther., 74: 245®254 ¤2003¥. 10¥ Lin, Y. S., Dowling, A. L., Quigley, S. D., Farin, F. M., Zhang, J., Lamba, J., Schuetz, E. G. and Thummel, K. E.: Co-regulation of CYP3A4 and CYP3A5 and contribution to hepatic and intestinal midazolam metabolism. Mol. Pharmacol., 62: 162®172 ¤2002¥. 11¥ Fukuen, S., Fukuda, T., Maune, H., Ikenaga, Y., Yamamoto, I., Inaba, T. and Azuma, J.: Novel detection assay by PCR-RFLP and frequency of the CYP3A5 SNPs, CYP3A5*3 and *6, in a Japanese population. Pharmacogenetics, 12: 331®334 ¤2002¥. 12¥ Katz, D. A., Carr, R., Grimm, D. R., Xiong, H., Holley-Shanks, R., Mueller, T., Leake, B., Wang, Q., Han, L., Wang, P. G., Edeki, T., Sahelijo, L., Doan, T., Allen, A., Spear, B. B. and Kim, R. B.: Organic anion transporting polypeptide 1B1 activity classified by SLCO1B1 genotype influences atrasentan pharmacokinetics. Clin. Pharmacol. Ther., 79: 186®196 ¤2006¥. 13¥ Nozawa, T., Nakajima, M., Tamai, I., Noda, K., Nezu, J., Sai, Y., Tsuji, A. and Yokoi, T.: Genetic polymorphisms of human organic anion transporters OATP-C ¤SLC21A6¥ and OATP-B ¤SLC21A9¥: allele frequencies in the Japanese population and functional analysis. J. Pharmacol. Exp. Ther., 302: 804®813 ¤2002¥. 14¥ Tsujimoto, M., Dan, Y., Hirata, S., Ohtani, H. and Sawada, Y.: Influence of SLCO1B3 gene polymorphism on the pharmacokinetics of digoxin in terminal renal failure. Drug Metab. Pharmacokinet., 23: 406®411 ¤2008¥. 15¥ Mougey, E. B., Feng, H., Castro, M., Irvin, C. G. and Lima, J. J.: Absorption of montelukast is transporter mediated: a common variant of OATP2B1 is associated with reduced plasma concentrations and poor response. Pharmacogenet. Genomics, 19: 129®138 ¤2009¥.
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Copyright © 2011 by the Japanese Society for the Study of Xenobiotics (JSSX)