Pharmacokinetic study of metformin to compare voglibose/metformin fixed-dose combination with coadministered voglibose and metformin.

The aim of this study was to compare the pharmacokinetic characteristics of metformin between a fixed-dose combination (FDC) of voglibose/metformin and coadministered individual voglibose and metformin tablets in healthy Korean volunteers under fasting conditions. A randomized, open-label, single-dose, two-treatment, two-way crossover study with a 7-day wash-out period was conducted. Plasma samples were collected for up to 24 hours and were analyzed for metformin using a validated liquid chromatography tandem mass-spectrometry (LC/MS). A noncompartmental method was used to calculate the pharmacokinetic parameters. Vital signs and adverse events were monitored, and physical examinations and laboratory tests were conducted to evaluate safety. In total, 28 subjects completed the study. The geometric mean ratio (GMR) and the 90% confidence interval (CIs) of Cmax and AUC0-t of metformin were 102.4 (94.5-111.0) and 107.1 (100.1-114.7), respectively. In total, 7 adverse drug reactions occurred in 4 subjects during the study; of these, 3 cases were from 3 subjects in the test treatment group, and 4 cases were from 3 subjects in the reference treatment group. All adverse drug reactions had been reported previously, and all subjects recovered fully without any sequelae. In conclusion, the pharmacokinetic profiles of metformin in two different study treatments, a voglibose/metformin FDC vs. the coadministration of the individual formulations, met the regulatory criteria for bioequivalence in healthy Korean subjects under fasting conditions. There was no significant difference in safety profiles between the two treatments.

The effect of Ginkgo biloba extracts on the pharmacokinetics and pharmacodynamics of cilostazol and its active metabolites in healthy Korean subjects.

AIMS: The primary objective of this study was to evaluate the effects of Ginkgo biloba extracts (GBE) on the pharmacokinetics of cilostazol and its metabolites. The secondary objective was to assess the effect of GBE on the pharmacodynamics of cilostazol. METHODS: A randomized, double-blind, two-way crossover study was conducted with 34 healthy Korean subjects. All subjects were given an oral dose of cilostazol (100 mg) plus GBE (80 mg) or cilostazol (100 mg) plus placebo twice daily for 7 days. Plasma concentrations of cilostazol and its active metabolites (3,4-dehydrocilostazol and 4'-trans-hydroxycilostazol) were measured using liquid chromatography-tandem mass spectroscopy on day 7 for pharmacokinetic assessment. The adenosine diphosphate-induced platelet aggregation and bleeding time were measured at baseline and on day 7 for pharmacodynamic assessment. RESULTS: The geometric mean ratios of area under the concentration-time curve for dosing interval for cilostazol plus GBE vs. cilostazol plus placebo were 0.96 (90% confidence interval, 0.89-1.03; P = 0.20) for cilostazol, 0.96 (90% confidence interval, 0.90-1.02; P = 0.30) for 3,4-dehydrocilostazol and 0.98 (90% confidence interval, 0.93-1.03; P = 0.47) for 4'-trans-hydroxycilostazol. The change of aggregation after administration of cilostazol plus GBE seemed to be 1.31 times higher compared with cilostazol plus placebo, without statistical significance (P = 0.20). There were no significant changes in bleeding times and adverse drug reactions between the treatments. CONCLUSIONS: Co-administration of GBE showed no statistically significant effects on the pharmacokinetics of cilostazol in healthy subjects. A large cohort study with long-term follow-up may be needed to evaluate the possible pharmacodynamic interaction between cilostazol and GBE, given that there was a remarkable, but not statistically significant, increase in inhibition of platelet aggregation.

Effect of voglibose on the pharmacokinetics of metformin in healthy Korean subjects.

OBJECTIVE: The objective of this study was to evaluate the effects of voglibose on the pharmacokinetics of metformin. METHODS: A randomized, open-label, two-way crossover study with a 7-day washout period was conducted. All subjects were given an oral dose of metformin with or without voglibose 3 x daily for 7 days. Plasma concentrations of metformin on day 7 were measured using high performance liquid chromatography (HPLC) with UV detection for pharmacokinetic assessment Vital signs and adverse events were monitored, and physical examinations and laboratory tests were conducted to evaluate safety. RESULTS: 22 subjects completed the study. The geometric mean ratios for C(ss,max) of metformin (metformin plus voglibose vs. metformin only) were 0.98 (90% CI, 0.92 - 1.05; p > 0.05) and for AUC-τ, the ratio was 0.99 (90% CI, 0.92 - 1.06; p > 0.05). There were no significant differences in adverse drug reactions between metformin with and without voglibose. However, the incidence of adverse events was higher in period 1 than in period 2 (16 cases vs. 1 case, p < 0.001). CONCLUSIONS: Co-administration of metformin and voglibose had no statistically or clinically significant effects on the pharmacokinetics of metformin in healthy subjects. The pharmacodynamic interaction study to evaluate the effect of metformin on the pharmacodynamics of voglibose is in progress.

Effect of HNF4α genetic polymorphism G60D on the pharmacokinetics of CYP2D6 substrate tolterodine in healthy Korean individuals.

Hepatocyte nuclear receptor 4α (HNF4α) plays a central role in regulating human drug-metabolizing enzymes. Our previous study suggested that the newly identified polymorphism G60D in the HNF4α gene may decrease its downstream CYP2D6 activity in Asians. To confirm this effect in a clinical setting, we carried out a full pharmacokinetic study of a single oral dose of CYP2D6 substrate tolterodine in 30 healthy Korean individuals (HNF4α wild type: n = 24; HNF4α G60D heterozygotes: n = 6) who were pregenotyped for CYP2D6. Our study showed HNF4α G60D to be an independent predictor for increased AUC0-∞, C max of tolterodine and increased AUC0-∞ of the active moiety (tolterodine+5-hydroxymethyl-tolterodine) (P<0.05). A significant proportion of the variance in these parameters (R = 0.81, 0.59, and 0.63, respectively; P<0.01) was explained together by CYP2D6 and HNF4α genotypes. Further investigation of HNF4α genetic polymorphisms may improve the predictability of CYP2D6 activity in different populations.

Effects of clopidogrel and itraconazole on the disposition of efavirenz and its hydroxyl metabolites: exploration of a novel CYP2B6 phenotyping index.

AIMS: To evaluate the effects of clopidogrel and itraconazole on the disposition of efavirenz and its hydroxyl metabolites in relation to the CYP2B6*6 genotype and explore potential phenotyping indices for CYP2B6 activity in vivo using a low dose of oral efavirenz. METHODS: We conducted a randomized three phase crossover study in 17 healthy Korean subjects pre-genotyped for the CYP2B6*6 allele (CYP2B6*1/*1, n = 6; *1/*6, n = 6; *6/*6, n = 5). Subjects were pretreated with clopidogrel (75 mg day(-1) for 4 days), itraconazole (200 mg day(-1) for 6 days), or placebo and then given a single dose of efavirenz (200 mg). The plasma (0-120 h) and urine (0-24 h) concentrations of efavirenz and its metabolites (7- and 8-hydroxyefavirenz and 8,14-dihydroxyefavirenz) were determined by LC/MS/MS. RESULTS: This study is the first to delineate quantitatively the full (phase I and II) metabolic profile of efavirenz and its three hydroxyl metabolites in humans. Clopidogrel pretreatment markedly decreased AUC(0,48 h), C(max) and Ae(0,24 h) for 8,14-dihydroxyefavirenz, compared with placebo; 95% CI of the ratios were 0.55, 0.73, 0.30, 0.45 and 0.25, 0.47, respectively. The 8,14-dihydroxyefavirenz : efavirenz AUC(0,120 h) ratio was significantly correlated with the weight-adjusted CL/F of efavirenz (r(2) ≈ 0.4, P < 0.05), differed with CYP2B6*6 genotype and was affected by clopidogrel pretreatment (P < 0.05) but not by itraconazole pretreatment. CONCLUSIONS: The disposition of 8,14-dihydroxy-EFV appears to be sensitive to CYP2B6 activity alterations in human subjects. The 8,14-dihydroxyefaviremz : efavirenz AUC(0,120 h) ratio is attractive as a candidate phenotyping index for CYP2B6 activity in vivo.

High-sensitive LC-MS/MS method for the simultaneous determination of mirodenafil and its major metabolite, SK-3541, in human plasma: application to microdose clinical trials of mirodenafil.

A high-sensitivity LC/MS/MS method was developed and validated for the simultaneous determination of mirodenafil and its major metabolite, SK-3541, in human plasma. Mirodenafil, SK-3541, and udenafil as an internal standard were extracted from plasma samples with methyl tert-butyl ether. Chromatographic separation was performed on a Luna phenyl-hexyl column (100 × 2.0 mm) with an isocratic mobile phase consisting of 5 mM ammonium formate and ACN (23:77, v/v) at a flow rate of 0.35 mL/min. Detection and quantification were performed using a mass spectrometer in selected reaction monitoring mode with positive ESI at m/z 532.3 → 296.1 for mirodenafil, m/z 488.1 → 296.1 for SK-3541, and m/z 517.3 → 283.2 for udenafil. The calibration curves were linear over a concentration range of 2-500 pg/mL using 0.5 mL plasma for the microdose of mirodenafil (100 µg). Analytical method validation of the clinical dose (100 mg), with a calibration curve range of 2-500 ng/mL using 0.025-mL plasma, was also conducted. The other LC-MS/MS conditions were similar to those used for the microdosing. Each method was applied successfully to pharmacokinetic studies after a microdose or clinical dose of mirodenafil to six healthy Korean male volunteers.

Effects of clopidogrel and clarithromycin on the disposition of sibutramine and its active metabolites M1 and M2 in relation to CYP2B6*6 polymorphism.

Plasma concentrations of sibutramine and its two active metabolites after single oral dose of sibutramine were determined in Korean healthy male subjects with different CYP2B6 genotypes (CYP2B6*1/*1, *1/*6 and *6/*6), either alone or after four-day pretreatment with clopidogrel or clarithromycin. The pretreatment with clopidogrel and clarithromycin raised the mean area under the concentration-time curve (AUC) of sibutramine by 163% and 255%, respectively. Co-administration of clarithromycin, combined with CYP2B6*6/*6 genotype, led to highest concentration of sibutramine. The molar sum AUC (M1 + M2) was raised by 35% in the clopidogrel phase but not significantly affected by clarithromycin or CYP2B6 genotype. The CYP2B6*6/*6 subjects in the clopidogrel phase showed the highest molar AUC (M1 + M2) among three genotype groups throughout the three phases. The exposure of sibutramine and its metabolites seemed to be associated with the CYP2B6 genotype. The treatment of clopidogrel significantly altered the disposition of active metabolites as well as sibutramine, but clarithromycin only affects the disposition of sibutramine. These results suggest that the perturbation of CYP2B6 activity may contribute to the inter-individual variation of sibutramine drug responses although the clinical relevance is remained to be established.

The disposition of three phosphodiesterase type 5 inhibitors, vardenafil, sildenafil, and udenafil, is differently influenced by the CYP3A5 genotype.

OBJECTIVES: This study was conducted to compare the effect of CYP3A5*3 genotype on the disposition of three phosphodiesterase type 5 inhibitors (PDE5Is), vardenafil, sildenafil, and udenafil, because our previous in-vitro microsomal incubation study showed that the relative contribution of CYP3A5 enzyme to their metabolism was different among these PDE5Is. METHODS: An open-label three-way crossover study was performed with a single oral dose of PDE5Is (20 mg vardenafil, 100 mg sildenafil, or 200 mg udenafil) in 21 healthy men carrying CYP3A5*1/*1, *1/*3, or *3/*3. After each dose, plasma concentrations of the parents and their major metabolites were measured up to 24 or 48 h. RESULTS: The AUC(∞) and C(max) of vardenafil were 2.9-fold and 3.1-fold higher in CYP3A5*3/*3 carriers than in individuals with CYP3A5*1/*1 (P=0.003 and 0.002, respectively). The AUC(∞) and C(max) of sildenafil were 1.5-fold and 1.7-fold higher in CYP3A5*3/*3 carriers compared with individuals with CYP3A5*1/*1, but the statistical difference of both parameters among genotype groups was not observed. The disposition of udenafil differed little among groups in relation to the CYP3A5*3 allelic variant. CONCLUSION: These results suggest that the disposition of these PDE5Is are differently influenced by the CYP3A5*3 genotype of individual participants. The CYP3A5*3 genotype affects the oral disposition of vardenafil significantly. The pharmacokinetic diversity of PDE5Is in relation to CYP3A5 genotype may lead to the clinical response variation and remains to be evaluated.

Discovery of a novel allelic variant of CYP2C8, CYP2C8*11, in Asian populations and its clinical effect on the rosiglitazone disposition in vivo.

The objectives of this study were to identify the genetic variants of CYP2C8, analyze CYP2C8 single nucleotide polymorphisms (SNPs), and characterize their functional consequences in the CYP2C8 substrate drug rosiglitazone in humans. The direct full sequencing of CYP2C8 genomic DNA was performed in a Korean population (n = 50). A total of 17 CYP2C8 variants including a novel coding variant (E274Stop) were identified. The novel CYP2C8 E274Stop variant was assigned as CYP2C8*11 by the Human Cytochrome P450 (CYP) Allele Nomenclature Committee. Seventeen SNPs were used to characterize linkage disequilibrium, haplotype structures, and haplotype tagging SNPs. Genotyping for CYP2C8*11 in an extended set of Koreans (n = 400), whites (n = 100), Han Chinese (n = 348), Vietnamese (n = 100), and African Americans (n = 93) was performed by a newly developed pyrosequencing method. The frequency of CYP2C8*11 was 0.3% in Koreans, 1% in Vietnamese, and 0.14% in Chinese. However, none of the whites or African Americans contained the CYP2C8*11 allele. Subjects with CYP2C8*1/*11 exhibited higher plasma concentration-time profiles of rosiglitazone than those of nine control subjects carrying CYP2C8*1/*1. The area under the concentration-time curve and peak plasma concentration of rosiglitazone in individuals carrying CYP2C8*1/*11 (n = 5) were 54 and 34% higher than the mean values observed in the control subjects carrying CYP2C8*1/*1 (P = 0.015 and P = 0.025, respectively). In summary, this is the first report to characterize the allele frequency and haplotype distribution of CYP2C8 in a Korean population, and it provides functional analysis of a new variant CYP2C8*11. Our findings suggest that individuals carrying CYP2C8*11, a null allele found in Asians only, may have lower activity for metabolizing CYP2C8 substrate drugs.

Serum levels of IL-18 and sIL-2R in patients with alopecia areata receiving combined therapy with oral cyclosporine and steroids.

This study was to determine which immunologic factors contribute to the prognosis of patients with alopecia areata (AA) who were receiving oral cyclosporine A and methylprednisolone. Patients with > 25% hair regrowth were defined as responders, and patients exhibiting < or = 25% regrowth were poor-responders. The serum levels of IL-18 and soluble IL-2 receptor (sIL-2R) were measured at baseline in 21 patients with AA and 22 control subjects. The mean serum level of IL-18 in the patients with extensive AA was significantly higher than that in the control subjects. The mean serum concentration of sIL-2R in the AA patients significantly decreased after 1 month of treatment. The mean basal serum level of IL-18 was highest in the responder, whereas the baseline level of sIL-2R was significantly higher in the poor-responder group than other groups. In conclusion, increased serum sIL-2R level and lower IL-18 level at baseline was associated with a poor prognosis in patients with AA.

Effects of woohwangcheongsimwon suspension on the pharmacokinetics of bupropion and its active metabolite, 4-hydroxybupropion, in healthy subjects.

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT: Woohwangcheongsimwon suspension has traditionally been used for the treatment and prevention of stroke, hypertension, palpitations, convulsions and unconsciousness in various Asian countries. Woohwangcheongsimwon suspensions showed an inhibitory effect on CYP2B6 activity in vitro. Two terpenoids, borneol and isoborneol, are major constituents of woohwangcheongsimwon suspension, and show a competitive inhibition of CYP2B6 with K(i) values of 9.5 and 5.9 microM, respectively. Bupropion undergoes metabolic transformation to the active metabolite, 4-hydroxybupropion, primarily via CYP2B6 both in vivo and in vitro. It is often used as a CYP2B6 substrate for clinical drug-drug interaction studies. Drug interactions may occur between woohwangcheongsimwon suspension and bupropion. WHAT THIS STUDY ADDS: Co-administration with woohwangcheongsimwon suspension did not alter the pharmacokinetics of bupropion or its metabolite, 4-hydroxybupropion. Dosage adjustment of bupropion is unnecessary in patients concomitantly administered the highest recommended daily dose of woohwangcheongsimwon suspension. AIMS: To examine the effects of woohwangcheongsimwon suspension on the pharmacokinetics of bupropion and its active metabolite, 4-hydroxybupropion, formed via CYP2B6 in vivo. METHODS: A two-way crossover clinical trial with a 2 week washout period was conducted in 14 healthy volunteers. In phases I and II, subjects received 150 mg bupropion with or without woohwangcheongsimwon suspension four times (at -0.17, 3.5, 23.5 and 47.5 h, with the time of bupropion administration taken as 0 h) in a randomized balanced crossover order. Bupropion and 4-hydroxybupropion plasma concentrations were measured for up to 72 h by LC-MS/MS. Urine was collected up to 24 h to calculate the renal clearance. In addition, the CYP2B6*6 genotype was also analyzed. RESULTS: The geometric mean ratios and 90% confidence interval of bupropion with woohwangcheongsimwon suspension relative to bupropion alone were 0.976 (0.917, 1.04) for AUC(0,infinity) and 0.948 (0.830,1.08) for C(max), respectively. The corresponding values for 4-hydroxybupropion were 0.856 (0.802, 0.912) and 0.845 (0.782, 0.914), respectively. The t(max) values of bupropion and 4-hydroxybupropion were not significantly different between the two groups (P > 0.05). The pharmacokinetic parameters of bupropion and 4-hydroxybupropion were unaffected by woohwangcheongsimwon suspension. CONCLUSIONS: These results indicate that woohwangcheongsimwon suspension has a negligible effect on the disposition of a single dose of bupropion in vivo. As a result, temporary co-administration with woohwangcheongsimwon suspension does not seem to require a dosage adjustment of bupropion.

Genetic polymorphism of hepatocyte nuclear factor-4alpha influences human cytochrome P450 2D6 activity.

UNLABELLED: Hepatocyte nuclear factor-4 alpha (HNF4A) is an essential transcriptional regulator for many genes that are expressed preferentially in the liver. Among the important functions of the liver is drug metabolism in response to xenobiotic exposure. Recent studies have suggested that HNF4A regulates the expression of cytochrome P450 (CYP), including CYP2D6 and CYP3A4, which show large individual variations in their activities. To understand the genetic factors that influence individual CYP activities, a genetic variant of HNF4A and the effects of genetic variants of HNF4A on CYP activity were investigated. Here, we report the identification of a novel coding variant of HNF4A that influences CYP2D6 activity in humans. After direct sequencing, a polymorphism search revealed the HNF4A G60D variant in Koreans. This variant was unable to bind to the recognition site in the CYP2D6 promoter and therefore lacked the regulatory function for this gene. Human liver specimens with the heterozygous HNF4A G60D genotype showed a tendency toward lower levels of CYP2D6 activity than the wild-type genotype in the same genetic background of CYP2D6. Furthermore, human subjects with the HNF4A G60D genotype tended to have lower CYP2D6 activity than those with the wild-type HNF4A. The HNF4A G60D variant was detected at low frequency in Asian populations, including Koreans, Chinese, and Vietnamese, and was not found in Africans or Caucasians. CONCLUSION: This is the first report to show that the genetic polymorphism of liver-enriched nuclear receptor HNF4A influences downstream CYP2D6 function in human subjects.

Identification of new CYP2C19 variants exhibiting decreased enzyme activity in the metabolism of S-mephenytoin and omeprazole.

Although many cases of interindividual variation in the metabolism of CYP2C19 drugs are explained by the CYP2C19*2, *3, and *17, a wide range of metabolic variation still occurs in people who do not carry these genetic variants. The objectives of this study were to identify new genetic variants and to characterize functional consequences of these variants in metabolism of CYP2C19 substrates. In total, 21 single-nucleotide polymorphisms including three new coding variants, V394M, E405K, and D256N, were identified by direct DNA sequencing in 50 randomly selected subjects and in individuals who exhibited an outlier phenotype response in the omeprazole study. Recombinant proteins produced from the coding variants V394M, E405K, and D256N were prepared by using an Escherichia coli expression system and purified. Metabolism of S-mephenytoin and omeprazole by V394M was comparable with that of the wild-type protein. E405K showed a moderate decrease in metabolism of the substrates. However, D256N exhibited a significantly decreased activity in S-mephenytoin metabolism, resulting in 50 and 76% decreases in V(max) and intrinsic clearance, respectively, compared with the wild type. This variant also exhibited a significant decrease in omeprazole metabolism in vivo. CYP2C19 D256N and E405K were assigned as CYP2C19*26 and *2D, respectively, by the Cytochrome P450 Nomenclature Committee. In summary, this report characterizes the allele frequency and haplotype distribution of CYP2C19 in a Korean population and provides functional analysis of new coding variants of the CYP2C19 gene. Our findings suggest that individuals carrying CYP2C19*26 would have lower activity for metabolizing CYP2C19 substrate drugs.

Liquid chromatography/tandem mass spectrometry method for the simultaneous determination of vardenafil and its major metabolite, N-desethylvardenafil, in human plasma: application to a pharmacokinetic study.

A rapid and sensitive LC-MS/MS method for the determination of vardenafil and its major metabolite, N-desethylvardenafil, in human plasma using sildenafil as an internal standard was developed and validated. The analytes were extracted from 0.25-mL aliquots of human plasma by liquid-liquid extraction, using 1 mL of ethyl acetate. Chromatographic separation was carried on a Luna C(18) column (50 mm x 2.0 mm, 3 microm) at 40 degrees C, with an isocratic mobile phase consisting of 10 mM ammonium acetate (pH 5.0) and acetonitrile (10:90, v/v), a flow rate of 0.2 mL/min, and a total run time of 2 min. Detection and quantification were performed using a mass spectrometer in the selected reaction-monitoring mode with positive electrospray ionization at m/z 489.1-->151.2 for vardenafil, m/z 460.9-->151.2 for N-desethylvardenafil, and m/z 475.3-->100.1 for the internal standard (IS), respectively. This assay was linear over a concentration range of 0.5-200 ng/mL with a lower limit of quantification of 0.5 ng/mL for both vardenafil and N-desethylvardenafil. The coefficient of variation for the assay precision was <13.6%, and the accuracy was >93.1%. This method was successfully applied to a pharmacokinetic study after oral administration of vardenafil 20mg tablet in Korean healthy male volunteers.

HPLC determination of irbesartan in human plasma: its application to pharmacokinetic studies.

A simple and rapid HPLC method using fluorescence detection was developed for determination of irbesartan in human plasma. Sample preparation was accomplished through a simple deproteinization procedure with 0.4 mL of acetonitrile containing 800 ng/mL of losartan (internal standard), and to a 0.1 mL plasma sample. Chromatographic separation was performed on a Zorbax Xclipse XDB C18 column (150 x 4.6 mm, i.d., 5 microm) at 40 degrees C. An isocratic mobile phase, acetonitrile:0.1% formic acid (37:63, v/v), was run at a flow-rate of 1.0 mL/min, and the column eluent was monitored using a fluorescence detector set at excitation and emission wavelengths of 250 and 370 nm, respectively. The retention times of irbesartan and losartan were 4.4 and 5.9 min, respectively. This assay was linear over a concentration range of 10-5000 ng/mL with a lower limit of quantification of 10 ng/mL. The coefficient of variation for this assay precision was less than 8.48%, and the accuracy exceeded 94.4%. The mean relative recoveries of irbesartan and losartan were 98.4 and 99.1%, respectively. This method was successfully applied for pharmacokinetic study after oral administration of irbesartan (300 mg) to 23 Korean healthy male volunteers.

The contributions of cytochromes P450 3A4 and 3A5 to the metabolism of the phosphodiesterase type 5 inhibitors sildenafil, udenafil, and vardenafil.

The role of the genetically polymorphic CYP3A5 in the metabolism of CYP3A substrates is unclear. We investigated the contributions of the CYP3A4 and CYP3A5 isoforms to the metabolism of the phosphodiesterase type 5 inhibitors (PDE5Is) sildenafil, udenafil, and vardenafil. In vitro incubation studies of sildenafil N-demethylation, udenafil N-dealkylation, and vardenafil N-deethylation were conducted using recombinant CYP3A enzymes and 15 human liver microsome (HLM) preparations with predetermined CYP3A5 genotypes. Recombinant CYP3A4 and CYP3A5 both produced N-desalkyl metabolites of sildenafil, udenafil, and vardenafil. The catalytic efficiency (Cl(int) = V(max)/apparent K(m)) of the rCYP3A5 isoform for vardenafil N-deethylation was about 3.2-fold that of rCYP3A4, whereas the intrinsic clearance rates for N-dealkylation of both sildenafil and udenafil were similar between rCYP3A5 and rCYP3A4. The metabolite formation activity was higher in HLMs heterozygous for the CYP3A5*3 allele (n = 9) than in HLMs homozygous for CYP3A5*3 (n = 6). These findings suggest that CYP3A5 and CYP3A4 play a significant role in the metabolism of PDE5Is. The genetic polymorphism of CYP3A5 may contribute to interindividual variability in the disposition of PDE5Is, especially vardenafil. Further in vivo studies are needed to confirm the effects of CYP3A5 genotypes on the pharmacokinetics of PDE5Is.

Cytochrome P450 2B6 catalyzes the formation of pharmacologically active sibutramine (N-{1-[1-(4-chlorophenyl)cyclobutyl]-3-methylbutyl}-N,N-dimethylamine) metabolites in human liver microsomes.

We identified cytochrome P450 (P450) isozymes that are involved in the formation of two active sibutramine (N-{1-[1-(4-chlorophenyl)-cyclobutyl]-3-methylbutyl}-N,N-dimethylamine) metabolites, M1 (N-{1-[1-(4-chlorophenyl)cyclobutyl]-3-methylbutyl}-N-methylamine) and M2 (1-[1-(4-chlorophenyl)cyclobutyl]-3-methylbutylamine), in humans using a combination chemical inhibition, correlation analyses in human liver microsomes (HLMs), and activity assays using recombinant P450s. Mechanism-based CYP2B6 inhibitors (i.e., clopidogrel, ticlopidine, and triethylenethiophoramide) significantly inhibited the formation of M1 from sibutramine and M2 from M1, respectively; in contrast, no effect was observed when using potent inhibitors of eight P450 isozymes (CYP1A2, CYP2A6, CYP2C8, CYP2C9, CYP2C19, CYP2D6, CYP2E1, and CYP3A). In addition, the formations of M1 from sibutramine (r = 0.694, p = 0.0029) and M2 from M1 (r = 0.834, p < 0.0001) were strongly correlated with CYP2B6-catalyzed bupropion hydroxylation in 16 different HLM panels. Furthermore, recombinant CYP2B6 catalyzed M1 and/or M2 formation at the highest rate among 10 P450s. Although recombinant CYP2C19, 3A4, and 3A5 also catalyzed, to a less extent, M1 formation at high substrate concentrations (>5 microM), those contributions might be minor considering usual concentrations of sibutramine and M1 in the clinical setting. The kinetics of M1 and/or M2 formation from sibutramine in HLMs were fitted by a two-enzyme model, and the mean apparent K(m) value (4.79 microM) for high-affinity component was similar to that observed in recombinant CYP2B6 (8.02 microM). In conclusion, CYP2B6 is the primary catalyst for the formation of sibutramine two active metabolites, which may suggest that pharmacogenetics and drug interactions of sibutramine in relation to CYP2B6 activity should be considered in the pharmacotherapy of sibutramine.

Duplex pyrosequencing assay of the 388A>G and 521T>C SLCO1B1 polymorphisms in three Asian populations.

BACKGROUND: We developed a method for detecting important SLCO1B1 polymorphisms and compared the haplotype frequencies in 3 Asian populations. METHODS: We designed a duplex pyrosequencing assay to detect simultaneously the 388A>G and 521T>C variants of SLCO1B1; this method can identify SLCO1B1*1b, SLCO1B1*5, and SLCO1B1*15. The method was validated by direct sequencing of 96 Korean subjects. In addition, duplex genotyping and the monoplex method were compared and validated with 469 Korean subjects. To characterize the haplotype frequencies based on the 2 polymorphisms, we genotyped 106 Chinese and 104 Vietnamese subjects, as well as Korean subjects, using the new method. RESULTS: The results showed 100% concordance among the monoplex and duplex pyrosequencing assays and direct sequencing method. The allele frequencies were similar in the 3 Asian populations: the most common allele was SLCO1B1*1b, while SLCO1B1*5 was rare or absent. The frequencies of functional SLCO1B1*15 alleles differed statistically between Chinese (8.2%) and Korean (14.0%) and Vietnamese (16.3%) (p<0.05, chi(2)-test). CONCLUSIONS: The duplex pyrosequencing assay appears to be an accurate, rapid, and cost-effective genotyping method to detect major SLCO1B1 important alleles in Asian populations.

Adjunctive treatment with a dopamine partial agonist, aripiprazole, for antipsychotic-induced hyperprolactinemia: a placebo-controlled trial.

OBJECTIVE: Hyperprolactinemia and associated side effects often occur with antipsychotics. The authors investigated the effect of adjunctive treatment with aripiprazole on hyperprolactinemia and psychopathology in patients with schizophrenia maintained with haloperidol. METHOD: Fifty-six patients with hyperprolactinemia taking haloperidol were enrolled. Haloperidol dose was fixed; aripiprazole was dosed at 15 mg/day for the first 4 weeks, then 30 mg/day for the following 4 weeks. Serum prolactin, haloperidol, and aripiprazole levels were measured. Symptoms and side effects were assessed with the Brief Psychiatric Rating Scale (BPRS), Scale for the Assessment of Negative Symptoms, Clinical Global Impression symptom scale, Simpson-Angus Rating Scale, and Barnes Akathisia Rating Scale at weeks 1, 2, 4, 6, and 8. RESULTS: Prolactin levels of patients receiving aripiprazole significantly decreased over time, demonstrating a significant time effect and a time-by-group interaction. In the aripiprazole group, 88.5% of patients at week 8 had prolactin levels normalize compared to 3.6% of patients receiving placebo. Among 11 female patients with menstrual disturbances randomly assigned to aripiprazole, seven patients regained menstruation during the study, whereas none receiving placebo did. Plasma levels of haloperidol were not significantly altered. No significant time effect and time-by-group interactions on BPRS, Scale for the Assessment of Negative Symptoms, and Simpson-Angus Rating Scale scores were noted. CONCLUSIONS: Adjunctive aripiprazole treatment reversed hyperprolactinemia in both sexes, resulting in reinstatement of menstruation in female patients, with no significant effects on psychopathology and extrapyramidal symptoms. Aripiprazole has higher affinity to dopamine D(2) receptors than haloperidol, which is the likely cause of this observation.

Effect of CYP3A5*3 genotype on the pharmacokinetics and pharmacodynamics of alprazolam in healthy subjects.

OBJECTIVE: Our objective was to evaluate the effect of the CYP3A5 genotype on the pharmacokinetics and pharmacodynamics of alprazolam in healthy volunteers. METHODS: Nineteen healthy male volunteers were divided into 3 groups on the basis of the genetic polymorphism of CYP3A5. The groups comprised subjects with CYP3A5*1/*1 (n=5), CYP3A5*1/*3 (n=7), or CYP3A5*3/*3 (n=7). After a single oral 1-mg dose of alprazolam, plasma concentrations of alprazolam were measured up to 72 hours, together with assessment of psychomotor function by use of the Digit Symbol Substitution Test, according to CYP3A5 genotype. RESULTS: The area under the plasma concentration-time curve for alprazolam was significantly greater in subjects with CYP3A5*3/*3 (830.5+/-160.4 ng . h/mL [mean+/-SD]) than in those with CYP3A5*1/*1 (599.9+/-141.0 ng . h/mL) (P=.030). The oral clearance of alprazolam was also significantly different between the CYP3A5*1/*1 group (3.5+/-0.8 L/h) and CYP3A5*3/*3 group (2.5+/-0.5 L/h) (P=.036). Although a trend was noted for the area under the Digit Symbol Substitution Test score change-time curve (area under the effect curve) to be greater in subjects with CYP3A5*3/*3 (177.2+/-84.6) than in those with CYP3A5*1/*1 (107.5+/-44), the difference did not reach statistical significance (P=.148). CONCLUSIONS: The CYP3A5*3 genotype affects the disposition of alprazolam and thus influences the plasma levels of alprazolam.