Carvedilol is a b-adrenoceptor antagonist used clinically to treat chronic heart failure as well as hypertension, angina pectoris, and cardiac arrhythmias.1-4) Carvedilol is highly lipophilic and eliminated predominantly by hepatic metabolism, with renal excretion accounting for only 0.3% of the administered dose.5) The drug is absorbed rapidly from the gastrointestinal tract after oral administration; however, the amount of unchanged drug excreted in the feces was 23% of the administered dose probably because of incomplete intestinal absorption.6) In addition, orally administered carvedilol undergoes stereoselective first-pass metabolism, and the maximal plasma concentration of R-enantiomer with low bblocking activity is approximately 2-fold higher than that of S-enantiomer with high b-blocking activity.6) The mean absolute bioavailability of R-and S-enantiomer in humans is 31% and 15%, respectively. 7)In the previous study, we investigated the effect of genetic polymorphisms of cytochrome P450 (CYP) 2D6 on the pharmacokinetics of R-and S-carvedilol in 23 healthy Japanese volunteers.8) The large interindividual variability was observed in the pharmacokinetics of carvedilol, and the coefficient of variation of the weight (WT)-corrected oral clearance ((CL/F)/ WT) value among the subjects was 36.1%. In addition, the (CL/F)/WT value was highly correlated with the apparent distribution volume ((V/F)/WT) value among the subjects, suggesting that the interindividual difference in bioavailability (F) was at least partly responsible for the pharmacokinetic variability of carvedilol. The (CL/F)/WT and (V/F)/WT values of R-and S-carvedilol were significantly lower in healthy volunteers with at least one CYP2D6*10 allele than those with the CYP2D6*1/*1 and *1/*2 genotype. The result suggested that the systemic and/or pre-systemic metabolism of R-and S-carvedilol in the liver is significantly decreased in Japanese subjects with the CYP2D6*10 allele.Carvedilol is metabolized extensively via aliphatic sidechain oxidation and conjugation pathways, as well as the aromatic ring oxidation pathway which is mediated mainly by CYP2D6. 6) Oldham et al. reported that considerable metabolic activity for carvedilol is observed in CYP1A2, 2C9, 2D6, and 3A4. 9) On the other hand, it is still unclear whether the other P450s are involved in the metabolism of carvedilol. However, a substrate of CYP2C9, such as phenytoin, is partly catalyzed by another CYP2C subfamily, CYP2C19. 10)CYP3A5 is another important CYP3A protein in the liver, the substrate specificity of which largely overlaps with that of CYP3A4.11) In addition, Ohno et al. reported that UDP-glucuronosyltransferase (UGT) 1A1, 2B4, and 2B7 as well as human hepatic microsomes are capable of catalyzing the glucuronidation of carvedilol.12) Moreover, carvedilol has high affinity for the multidrug resistance 1 (MDR1) gene product P-glycoprotein (P-gp). Giessmann et al. reported that the intestinal expression of P-gp is a major variable in the disposition of carvedilol. 13)In the presen...

Carvedilol is a b-adrenoceptor antagonist, and has been clinically used to treat chronic heart failure as well as hypertension, angina pectoris, and cardiac arrhythmias. [1][2][3][4] Carvedilol is highly lipophilic and eliminated predominantly by hepatic metabolism, with renal excretion accounting for only 0.3% of the administered dose.5) The drug is absorbed rapidly from the gastrointestinal tract after oral administration; however, the amount of unchanged drug excreted in the feces was 23% of the administered dose probably because of incomplete intestinal absorption.6) In addition, orally administered carvedilol undergoes stereoselective first-pass metabolism, and the maximal plasma concentration of R-enantiomer with low b-blocking activity is approximately 2-fold higher than that of S-enantiomer with high b-blocking activity.6) The mean absolute bioavailability of R-and S-enantiomer in humans is 31% and 15%, respectively. 7)It was reported that CYP2D6 in microsomes derived from lymphoblastoid cells with human cDNA shows strong enzyme activity for the metabolism of R-and S-carvedilol. 8)Poor metabolism through CYP2D6 was found in 7% of Caucasian subjects, and two common defective alleles responsible for the poor metabolism are CYP2D6*4 and *5.9) The gene frequency of individual variants of CYP2D6 shows a marked interethnic difference, and poor metabolism is found in less than 1% of Asian subjects. 9) Among Asian extensive/ intermediate metabolizers, the three most common alleles of the CYP2D6 gene are CYP2D6*1, *2, and *10. The mutant allele of CYP2D6 (CYP2D6*2) does not affect the enzyme activity, whereas the CYP2D6*10 allele causes the low expression and affinity of CYP2D6. 10,11) In the present study, we estimated the pharmacokinetic parameters of R-and S-carvedilol in 23 healthy Japanese volunteers by the Bayesian method using a nonlinear mixed effects model (NONMEM) program. We then examined the effect of the CYP2D6 polymorphisms on the stereoselective pharmacokinetics of carvedilol. MATERIALS AND METHODS Subjects and Study ProtocolsTwenty-three healthy Japanese volunteers (19 men and 4 women) participated in this study. The age was between 22 and 44 years old (mean: 29.1), and the body weight was between 47 and 86 kg (mean: 64.7). They were given 5 mg (two 2.5 mg-tablets: 7 men and 2 women) or 10 mg (one 10 mg-tablet: 12 men and 2 women) of carvedilol (Artist ® tablet; Daiichi Pharmaceutical Co. Ltd., Tokyo, Japan) at least 2 h before a meal, because the peak blood drug concentrations are attained at 0.5-1 h after oral administration following an over night fast.12) Carvedilol was taken with a glass of water, and 5 ml of blood was taken at 2 and 6 h after dosing. All the subjects were physicians or pharmacists, and they chose the dose of carvedilol by themselves. The mean (ϮS.D.) body weight in the subjects taking 5 mg and 10 mg carvedilol was 57.9Ϯ6.7 kg and 69.1Ϯ 9.9 kg, respectively. They all gave written consent to participate in this study, which was approved by the ethics committee of Toyama Medica...

Mizoribine is an orally available immunosuppressive agent, which has been on the market since 1984 in Japan for the prevention of rejection in renal transplantation.1) In contrast to other immunosuppressive agents (e.g., azathioprine), mizoribine has been shown in animal experiments to lack oncogenicity and has shown clinically a low incidence of severe adverse drug reactions (such as myelosuppression and hepatotoxicity), making it useful in long-term immunosuppressive therapy.2) After oral administration, mizoribine is absorbed rapidly from the gastro-intestinal tract and distributed into living cells according to a concentration gradient between the extracellular and intracellular environment. It is completely eliminated from blood circulation within 24 h, and is excreted in urine (85%), feces (9.7%), and bile (Ͻ1%). 1,3) As elimination rate of mizoribine is highly dependent on renal function, low-dose mizoribine (1 to 3 mg/kg/d) was administered to patients whose renal function did not return soon after transplantation. However, renal function returns much earlier following transplantation due to the concomitant use of calcineurin inhibitors. High-dose mizoribine (5 mg/kg/d) has been administered since 1998 to a number of patients, and has been shown to be safe and well tolerated in renal transplant patients at doses up to 5 mg/kg/d. 4,5) In addition, Akiyama et al. reported that patients treated with Ն5 mg/kg/d of mizoribine showed about 20% fewer acute rejection episodes at 3 months post-transplantation than those with Ͻ5 mg/kg/d of mizoribine.4) Recently, phase 1 single-and multiple-dose studies have been carried out to confirm the safety, tolerability, and pharmacokinetics of higher-dose (up to 12 mg/kg/d) mizoribine.5) In the phase 1 study, no notable or clinically relevant abnormality was observed in the clinical laboratory values except for transient elevation in serum uric acid at the highest dose level (multiple dose of 12 mg/kg/d). 5)In the present study, to evaluate the pharmacokinetic characteristics of mizoribine in subjects with normal renal function, we estimated the population pharmacokinetic parameters of mizoribine using a nonlinear mixed effects model (NONMEM) program.6) Pharmacokinetic data for population analysis were obtained in the previous phase 1 study, where 24 healthy Caucasian male subjects participated in a singledose (3, 6, 9, 12 mg/kg) study, and 12 subjects participated in a multiple-dose (6, 12 mg/kg/d) study.5) In addition, to assess linearity and constancy in the pharmacokinetics of mizoribine, the pharmacokinetic parameters in individual 36 subjects were obtained from the population estimates according to Bayes' theorem using the NONMEM post-hoc option.6) We further evaluated the precision of Bayesian analysis in the sparse sampling protocol by using pharmacokinetic data obtained from 24 subjects in the single-dose study. 5) MATERIALS AND METHODSPharmacokinetic Data Serum mizoribine concentration data for population pharmacokinetic analysis were obtained in the previous stu...

Carvedilol is a b-adrenoceptor antagonist, clinically used to treat chronic heart failure as well as hypertension, angina pectoris, and cardiac arrhythmias.1) Orally administered carvedilol undergoes stereoselective first-pass metabolism, and the maximal plasma concentration of R-enantiomer with low b-blocking activity is approximately 2-fold higher than that of S-enantiomer with high b-blocking activity.2) Carvedilol is metabolized extensively via aliphatic sidechain oxidation, aromatic ring oxidation, and conjugation pathways.3) Oldham and Clarke 4) reported that oxidative activity for carvedilol is observed in cytochrome P450 (CYP) 2D6, 2C9, 3A4, and 1A2. In addition, Ohno et al. 5) reported that UDP-glucuronosyltransferase (UGT) 2B7, 2B4, and 1A1 are capable of catalyzing the glucuronidation of carvedilol. In the previous study, we examined the effect of CYP2D6*10, CYP2C9*3, CYP2C19*2, CYP2C19*3, CYP3A5*3, UGT2B7*2, UGT2B7*3, and the C3435T mutation of MDR1 on the pharmacokinetics of carvedilol in 54 Japanese volunteers. 2,6) The oral clearance (CL/F) and also volume of distribution (V/F) of R-and S-carvedilol were significantly lower in subjects with the CYP2D6*10 allele than those with CYP2D6*1/*1, *1/*2, or *2/*2 genotype, indicating that the systemic clearance (CL) and/or bioavailability (F) of both enantiomers is significantly altered in Japanese with the CYP2D6*10 allele. On the other hand, CYP2C9*3, CYP2C19*2, CYP2C19*3, CYP3A5*3, UGT2B7*2, UGT2B7*3, and the C3435T mutation of MDR1 did not affect the pharmacokinetics of R-and S-carvedilol in healthy Japanese. 2,6) Several pharmacokinetic studies have suggested that hepatic elimination of certain drugs via oxidative metabolism is impaired in patients with heart failure (HF) [7][8][9][10][11][12][13] ; that is, the CL/F value of prazosin after oral administration in HF patients was 46% of that in healthy subjects.7) It was also reported that the CL/F value of aminopyrine after oral administration in HF patients in the aminopyrine breath test was 24% of that in control subjects. 8) In addition, CL values of midazolam and quinidine (CYP3A4 substrates) after intravenous administration were decreased by 32% and 33% in HF patients, respectively. 9,10) The CL value of theophylline (CYP1A2 substrate) after intravenous administration was markedly decreased in HF patients. 11,12) Recently, population pharmacokinetic analysis has revealed that the CL/F value of mexiletine, which is mainly metabolized by CYP1A2 and CYP2D6, is reduced significantly in HF patients as compared with non-HF patients.13) However, it is still unclear whether the pharmacokinetics of R-and/or S-carvedilol is altered by HF. In the present study, therefore, we investigated the pharmacokinetics of R-and S-carvedilol in routinely treated Japanese patients with HF. MATERIALS AND METHODS Subjects and Study ProtocolTwenty-four Japanese patients with HF (16 men and 8 women) participated in this study. Their age was between 45 and 91 years old (70.5Ϯ11.3 years), and their body weight was between 36...

Carvedilol is a b-adrenoceptor antagonist, and has been clinically used to treat chronic heart failure as well as hypertension, angina pectoris, and cardiac arrhythmias. [1][2][3][4] Carvedilol is highly lipophilic and is absorbed rapidly from the gastrointestinal tract after oral administration. Orally administered carvedilol undergoes stereoselective first-pass metabolism, and the blood concentration of R-enantiomer with very low b-blocking activity is approximately 2-fold higher than that of S-enantiomer with high b-blocking activity. 5,6) Both enantiomers are eliminated predominantly by hepatic metabolism, with renal excretion accounting for only 0.3% of the administered dose. 7) Carvedilol is metabolized extensively via aliphatic side-chain oxidation, aromatic ring oxidation, and conjugation pathways.8) Oldham and Clarke reported that oxidative activity for carvedilol is observed in cytochrome P450 (CYP) 2D6, 2C9, 3A4, and 1A2. 9) In addition, Ohno et al. reported that UDP-glucuronosyltransferase (UGT) 2B7, 2B4, and 1A1 are capable of catalyzing the glucuronidation of carvedilol. 10) However, it is still unclear which enzyme is responsible for the stereoselective presystemic clearance of carvedilol. Furthermore, although CYP3A4 and several UGTs are expressed in intestinal epithelial cells, it is also unknown whether the intestine as well as the liver is involved in the first-pass metabolism of carvedilol.The approach for investigating intestinal drug absorption and metabolism is to use human intestinal cell lines, such as the frequently used line Caco-2. This line spontaneously differentiates, after which it shows enterocyte-like morphology and forms polarized monolayers via tight junctions. It also expresses various transporters and efflux pumps such as P-glycoprotein.11,12) Therefore, it has been utilized to examine the mechanism responsible for the intestinal absorption of various compounds. 12,13) In addition, several UGTs, such as UGT1A1, 1A6, and 2B7, are expressed in Caco-2 cells, and the expression of some UGTs is induced by aromatic hydrocarbon receptor (AhR) ligands, such as b-naphthoflavone (b-NF).14,15) Therefore, glucuronidation of drugs in the intestine has been studied using Caco-2 cells. [16][17][18] In contrast, the Caco-2 cell line had not been employed to examine the intestinal metabolism of CYP3A4 substrates due to its lack of CYP3A4 expression. Recently, however, it has been reported that CYP3A4 in Caco-2 cells is induced by 1a,25-dihydroxyvitamin D 3 (VD 3 ). 11,19) The finding suggests that this cell line may also be utilized to investigate intestinal drug metabolism by CYP3A4. In the present study, we investigated whether carvedilol is metabolized stereoselectively in Caco-2 cells, and also evaluated the changes in the metabolic rate of carvedilol in b-NF-and VD 3 -treated Caco-2 cells. MATERIALS AND METHODS MaterialsCarvedilol was kindly supplied by Daiichi Pharmaceutical (Tokyo, Japan). b-NF was obtained from Nacalai Tesque (Kyoto, Japan). VD 3 and 3Ј-azido-3Ј-deoxythimidine (AZT...