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Aims The purpose of this study was to explore clinical markers reflecting developmental changes in drug clearance by preterm infants. Methods Preterm infants administered aminophylline or theophylline to treat apnoea of prematurity were enrolled in this study. Trough and one of 2 h, 4 h or 6 h post-dose blood samples and urine samples were collected during steady state, to determine the concentrations of theophylline and its targeted metabolites. CYP1A2*1C and CYP1A2*1F genotypes were analyzed. Total, renal and nonrenal clearances of theophylline were calculated, and cytochrome P450 1A2 (CYP1A2) activity was obtained from the ratio of 1-methyluric acid and 3-methylxanthine to theophylline in urine. Multiple linear regression analysis was performed to evaluate the relationships between theophylline clearance and the clinical characteristics of preterm infants. Results A total of 152 samples from 104 preterm infants were analyzed. A strong association between the serum trough and urine theophylline concentrations was found (P

AIMS The aim of this study was to develop a population pharmacokinetic (PK) model of udenafil and its active metabolite, DA-8164, in healthy subjects and patients with hepatic impairment (HI) and to estimate the optimal dosing recommendations for patients with HI. METHODS An open label, three parallel group, age and weight matched control study was conducted in 18 volunteers, six healthy subjects (n = 6) and patients with mild (Child-Pugh class A, n = 6) and moderate HI (Child-Pugh class B, n = 6). Serial blood samples were collected for up to 72 h after a single administration of udenafil 100 mg. A population PK model was developed using non-linear mixed effects modelling (nonmem, ver. 7.2). The simulated data from the final PK model and original data of healthy subjects were compared to identify the optimal dose for patients with HI. RESULTS A two compartment model for both udenafil and DA-8164 best described the data. Prothrombin time on metabolic clearance of udenafil to DA-8164 was included in the final model as a covariate. Compared with the AUC(0,tlast ) value after administration of udenafil 100 mg to healthy subjects, the geometric mean ratios (95% confidence interval) after 100 mg and 75 mg udenafil administration were 1.21 (1.10, 1.32) and 0.74 (0.67, 0.81) in patients with mild HI, respectively. Meanwhile, those were 1.55 (1.43, 1.67) and 1.02 (0.92, 1.12) in patients with moderate HI, respectively. CONCLUSIONS This study suggests that the recommended doses of udenafil are 100 mg and 75 mg in patients with mild and moderate HI, respectively.

Aims HM30181 is a third generation P-glycoprotein (P-gp) inhibitor currently under development. The objectives of this study were to evaluate the effects of a single dose of HM30181 on the pharmacodynamics and pharmacokinetics of loperamide, a P-gp substrate, and to compare them with those of quinidine. Methods Eighteen healthy male subjects were administered loperamide alone (period 1) or with loperamide plus quinidine or HM30181 in period 2 or 3, respectively. In period 3, subjects randomly received one of three HM30181 doses: 15, 60 or 180 mg. Changes in pupil size, alertness, oxygen saturation and the oral bioavailability of loperamide were assessed in each period. In addition, the pharmacokinetics of HM30181 were determined. Results Pupil size, alertness and oxygen saturation did not change over time when loperamide alone or loperamide plus HM30181 was administered while HM30181 significantly increased the systemic exposure to loperamide, i.e. the geometric mean ratio (90% confidence interval) of AUC(0,tlast) for loperamide with and without HM30181 was 1.48 (1.08, 2.02). Co-administered quinidine significantly increased the systemic exposure to loperamide 2.2-fold (1.53, 3.18), which also markedly reduced pupil size, resulting in a decrease of 24.7 mm h in the area under the effect curve of pupil size change from baseline compared with loperamide alone. Conclusions HM30181 inhibits P-gp mainly in the intestinal endothelium, which can be beneficial because pan-inhibition of P-gp, particularly in the brain, could lead to detrimental adverse events. Further studies are warranted to investigate adequately the dose–exposure relationship of HM30181, along with its duration of effect.

The purpose of this study was to explore clinical markers reflecting developmental changes in drug clearance by preterm infants.Preterm infants administered aminophylline or theophylline to treat apnoea of prematurity were enrolled in this study. Trough and one of 2 h, 4 h or 6 h post-dose blood samples and urine samples were collected during steady state, to determine the concentrations of theophylline and its targeted metabolites. CYP1A2*1C and CYP1A2*1F genotypes were analyzed. Total, renal and nonrenal clearances of theophylline were calculated, and cytochrome P450 1A2 (CYP1A2) activity was obtained from the ratio of 1-methyluric acid and 3-methylxanthine to theophylline in urine. Multiple linear regression analysis was performed to evaluate the relationships between theophylline clearance and the clinical characteristics of preterm infants.A total of 152 samples from 104 preterm infants were analyzed. A strong association between the serum trough and urine theophylline concentrations was found (P 0.001). Total, renal and nonrenal clearances of theophylline were 0.50 ± 0.29 ml kgCYP1A2 activity can be monitored using noninvasive random urine samples, and it can be used to assess developmental changes in theophylline clearance by preterm infants.

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT • Atenolol is an antihypertensive drug, of which negligible amounts are metabolized. • Fruit juices may decrease the oral absorption of drugs by inhibiting intestinal drug transporters, as demonstrated in vitro and in vivo. WHAT THIS STUDY ADDS • The pharmacokinetic characteristics of atenolol were determined according to the SLCO2B1 genotype after apple juice administration in healthy Korean volunteers. • Apple juice ingestion markedly reduced the systemic exposure to atenolol, but genetic variations in SLCO2B1 were unlikely to contribute substantial variability to the pharmacokinetics of atenolol. AIM Fruit juice reduces the plasma concentrations of several β-adrenoceptor blockers, likely by inhibiting OATP2B1-mediated intestinal absorption. The aim of this study was to investigate the effects of apple juice on the pharmacokinetics of atenolol. METHODS Twelve healthy Korean volunteers with genotypes of SLCO2B1 c.1457C> T (*1/*1 (n= 6) and *3/*3 (n= 6)) were enrolled in this study. In a three-phase, one-sequence crossover study, the pharmacokinetics (PK) of atenolol was evaluated after administration of 50 mg atenolol. Subjects received atenolol with either 300 ml water, 1200 ml apple juice or 600 ml apple juice. RESULTS Apple juice markedly reduced the systemic exposure to atenolol. The geometric mean ratios (95% confidence intervals) of apple juice : water were 0.18 (0.13, 0.25, 1200 ml) and 0.42 (0.30, 0.59, 600 ml) for the AUC(0,tlast). In this study, the PK parameters of atenolol responded in a dose-dependent manner to apple juice. CONCLUSIONS Apple juice markedly reduced systemic exposure to atenolol. The genetic variation of SLCO2B1 c.1457C>T had a minimal effect on the pharmacokinetics of atenolol when the drug was administered with water or apple juice.

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT • The importance of efficient drug development using biomarkers has been increasingly emphasized, from preclinical studies to clinical trials. • However, as yet few ‘validated’ or ‘qualified’ biomarkers are used in early-stage drug development in terms of clinical pharmacology and disease pathophysiology. WHAT THIS STUDY ADDS • This first-time-in-human study provides evidence of the pharmacological activity of LC15-0444 in humans, by using dipeptidyl peptidase IV activity and active glucagon-like peptide-1 concentrations. • LC15-0444 possesses pharmacokinetic and pharmacodynamic characteristics that support a once-daily dosing regimen. AIMS LC15-0444 is a selective and competitive inhibitor of dipeptidyl peptidase (DPP) IV with potential for the treatment of Type 2 diabetes. The aim was to investigate the pharmacokinetic (PK) and pharmacodynamic (PD) profiles after multiple oral ascending doses of LC15-0444 in healthy male subjects. METHODS A dose block-randomized, double-blind, placebo-controlled, parallel group study was performed in three groups with 10 subjects (eight for active drug; two for placebo) per group; each group received 200, 400 or 600 mg of LC15-0444 once daily for 10 days. Blood and urine samples were collected up to 24 h after the first dosing and up to 72 h after the last dosing. RESULTS The LC15-0444 concentration–time profiles exhibited characteristics of multicompartment disposition. No dose- or time-dependent change in PK parameters was observed. Mean elimination half-life was in a range 16.6–20.1 h in the dose groups. Mean renal clearance and fraction of unchanged drug excreted in urine was 18.6–21.9 and 0.40–0.48 l h−1, respectively. In the steady state, mean accumulation ratios by dose groups were between 1.22 and 1.31. More than 80% inhibition of DPP IV activity from baseline was sustained for >24 h in all dose groups. CONCLUSIONS This study provides evidence of the pharmacological activity of LC15-0444 in humans. LC15-0444 possesses PK and PD characteristics that support a once-daily dosing regimen.

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT • The phosphodiesterase (PDE) type 5 inhibitor is a widely used agent that facilitates penile erection. • Udenafil is newly developed as a PDE-5 inhibitor. WHAT THIS STUDY ADDS • This is the first study to determine the safety, tolerability and pharmacokinetics of udenafil in healthy subjects. • Udenafil was safe and well tolerated in healthy Korean subjects. • The AUC and Cmax of udenafil increased supraproportionally with increasing dose upon single administration, but there was no significant drug accumulation upon multiple administrations. AIM To evaluate the safety, tolerability and pharmacokinetics (PK) of udenafil, a novel phosphodiesterase type 5 inhibitor. METHODS A double-blind, randomized, placebo-controlled, dose-rising, parallel-group, single- and multiple-dose study was conducted in healthy Korean subjects. The subjects were allocated to single-dose groups of 25, 50, 100, 200 or 300 mg (eight subjects in each dose group, including two placebos), or to multiple-dose groups of 100 or 200 mg (once-daily dosing for 7 days; nine subjects in each dose group, including three placebos). Serial samples of blood and urine were collected after oral administration and the drug concentrations in plasma and urine were determined by high-performance liquid chromatography. Safety and tolerability were evaluated by monitoring clinical laboratory parameters and adverse events. RESULTS Udenafil reached peak plasma concentrations at 0.8–1.3 h, and then declined mono-exponentially with a terminal half-life of 7.3–12.1 h in the single-dose study. The area under the time–concentration curves (AUC) and maximum plasma concentrations (Cmax) increased supraproportionally with increasing dose in the single-dose study. During multiple dosing, a steady state was reached at 5 days and little accumulation occurred after repeated dosing for 7 days. Udenafil was generally well tolerated in these healthy subjects, and no serious adverse events occurred. CONCLUSIONS Udenafil was safe and well tolerated in healthy volunteers. The AUC and Cmax of udenafil increased supraproportionally with increasing dose upon single administration, but there was no significant drug accumulation upon multiple administrations.

The aim of this study was to develop a population pharmacokinetic (PK) model of udenafil and its active metabolite, DA-8164, in healthy subjects and patients with hepatic impairment (HI) and to estimate the optimal dosing recommendations for patients with HI.An open label, three parallel group, age and weight matched control study was conducted in 18 volunteers, six healthy subjects (n = 6) and patients with mild (Child-Pugh class A, n = 6) and moderate HI (Child-Pugh class B, n = 6). Serial blood samples were collected for up to 72 h after a single administration of udenafil 100 mg. A population PK model was developed using non-linear mixed effects modelling (nonmem, ver. 7.2). The simulated data from the final PK model and original data of healthy subjects were compared to identify the optimal dose for patients with HI.A two compartment model for both udenafil and DA-8164 best described the data. Prothrombin time on metabolic clearance of udenafil to DA-8164 was included in the final model as a covariate. Compared with the AUC(0,tlast ) value after administration of udenafil 100 mg to healthy subjects, the geometric mean ratios (95% confidence interval) after 100 mg and 75 mg udenafil administration were 1.21 (1.10, 1.32) and 0.74 (0.67, 0.81) in patients with mild HI, respectively. Meanwhile, those were 1.55 (1.43, 1.67) and 1.02 (0.92, 1.12) in patients with moderate HI, respectively.This study suggests that the recommended doses of udenafil are 100 mg and 75 mg in patients with mild and moderate HI, respectively.

Aims The pharmacokinetics of omeprazole and its metabolites in healthy subjects were evaluated to determine if a single dose of moclobemide inhibited CYP2C19 activity. Methods Sixteen volunteers, of whom eight were extensive metabolizers (EM) and eight were poor metabolizers for CYP2C19, participated in two studies. Venous blood samples were collected for 24 h after oral ingestion of 40 mg omeprazole with or without 300 mg moclobemide coadministration. The pharmacokinetic change of omeprazole, omeprazole sulphone and 5-hydroxyomeprazole concentrations were assessed to test for an interaction between omeprazole and moclobemide. Results The coadministration of moclobemide in EMs approximately doubled the mean AUC (from 1834 to 3760 ng ml−1 h) and Cmax (from 987 to 1649 ng ml−1) of omeprazole, and increased the AUC of omeprazole sulphone without changing AUC ratio of omeprazole to omeprazole sulphone. Moclobemide coadministration more than doubled the AUC ratio of omeprazole to 5-hydroxyomeprazole (from 2.5 to 5.3) in EMs, too. There was a significant decrease in Cmax and AUC of 5-hydroxyomeprazole in PMs but no significant changes were seen in the results for omeprazole and omeprazole sulphone AUCs. Conclusions A single dose of moclobemide resulted in significant suppression of CYP2C19 activity in EMs. We conclude that physicians prescribing moclobemide should pay attention to its pharmacokinetic interactions even on the first day of coadministration with CYP2C19 substrates.

Fruit juice reduces the plasma concentrations of several β-adrenoceptor blockers, likely by inhibiting OATP2B1-mediated intestinal absorption. The aim of this study was to investigate the effects of apple juice on the pharmacokinetics of atenolol.Twelve healthy Korean volunteers with genotypes of SLCO2B1 c.1457CT (*1/*1 (n = 6) and *3/*3 (n = 6)) were enrolled in this study. In a three-phase, one-sequence crossover study, the pharmacokinetics (PK) of atenolol was evaluated after administration of 50 mg atenolol. Subjects received atenolol with either 300 ml water, 1200 ml apple juice or 600 ml apple juice.Apple juice markedly reduced the systemic exposure to atenolol. The geometric mean ratios (95% confidence intervals) of apple juice : water were 0.18 (0.13, 0.25, 1200 ml) and 0.42 (0.30, 0.59, 600 ml) for the AUC(0,t(last)). In this study, the PK parameters of atenolol responded in a dose-dependent manner to apple juice.Apple juice markedly reduced systemic exposure to atenolol. The genetic variation of SLCO2B1 c.1457CT had a minimal effect on the pharmacokinetics of atenolol when the drug was administered with water or apple juice.

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT • Almost all reported studies have investigated the pharmacokinetics of aripiprazole in healthy volunteers. • The pharmacokinetics of dehydroaripiprazole have not been identified in a combined model with aripiprazole. WHAT THIS STUDY ADDS • The data on aripiprazole and dehydroaripiprazole in psychiatric patients were modelled jointly using a population approach. • The apparent clearance of aripiprazole in cytochrome P450 (CYP) 2D6 intermediate metabolizers (IM) was approximately 60% of that in CYP2D6 extensive metabolizers (EM) having two functional alleles, but the exposure to dehydroaripiprazole in CYP2D6 IM was similar to that in EM. AIMS The aims of this study were to develop a combined population pharmacokinetic model for both aripiprazole and its active metabolite, dehydroaripiprazole, in psychiatric patients and to identify to what extent the genetic polymorphisms of cytochrome P450 (CYP) enzymes contribute to the variability in pharmacokinetics (PK). METHODS A population pharmacokinetic analysis was performed using NONMEM software based on 141 plasma concentrations at steady state from 80 patients receiving multiple oral doses of aripiprazole (10–30 mg day−1). RESULTS A one-compartment model with first-order kinetics for aripiprazole and dehydroaripiprazole each was developed to describe simultaneously the concentration data. The absorption rate constant was fixed to 1.06 h−1. The typical value of apparent distribution volume of aripiprazole was estimated to be 192 l. Covariate analysis showed that CYP2D6 genetic polymorphisms significantly influenced the apparent clearance of aripiprazole (CL/F), reducing the interindividual variability on CL/F from 37.8% CV (coefficient of variation) to 30.5%. The CL/F in the CYP2D6 IMs was approximately 60% of that in CYP2D6 EMs having two functional alleles. Based on the CYP2D6 genotype, the metabolic ratios were calculated at 0.20–0.34. However, the plasma concentration : dose ratios of dehydroaripiprazole were not different across the CYP2D6 genotype. CONCLUSIONS This population pharmacokinetic model provided an adequate fit to the data for both aripiprazole and dehydroaripiprazole in psychiatric patients. The usefulness of CYP genotyping as an aid to select the starting dose should be further investigated.

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT • The only existing study of CYP2D6*10-associated alterations in flecainide pharmacokinetics was retrospective. • Paroxetine has been known as a strong inhibitor of CYP2D6. WHAT THIS STUDY ADDS • This study reports that the extent of drug interaction between flecainide and paroxetine is influenced by the CYP2D6*10 allele in healthy subjects, which is frequent in Asians. AIMS The objectives were to evaluate the effect of CYP2D6 genetic polymorphism on the pharmacokinetics of flecainide, and also on the extent of drug interaction with paroxetine as a CYP2D6 inhibitor after a single oral administration in healthy subjects. METHODS An open-label, two-period, single-sequence, cross-over study was performed in 21 healthy Korean male volunteers (seven for CYP2D6*1/*1 or *1/*2, group 1; seven for CYP2D6*1/*10, group 2; seven for CYP2D6*10/*10 or *10/*36, group 3). Subjects were administered 200 mg of flecainide on day 1. After a 7-day wash-out period, subjects were administered 20 mg of paroxetine from day 8 to 14, and 200 mg of flecainide on day 15. Blood sampling was performed up to 72 h after flecainide administration. RESULTS Terminal elimination half-life and mean residence time (MRT) were significantly different among three genotype groups after a single oral administration of flecainide (P = 0.021, 0.011, respectively). Area under the concentration–time curve, terminal elimination half-life and MRT increased significantly after paroxetine co-administration only in groups 1 and 2. CONCLUSIONS This study reports that the extent of drug interaction between flecainide and paroxetine is influenced by the CYP2D6*10 allele in healthy subjects, which is frequent in Asians.

The pharmacokinetics of omeprazole and its metabolites in healthy subjects were evaluated to determine if a single dose of moclobemide inhibited CYP2C19 activity.Sixteen volunteers, of whom eight were extensive metabolizers (EM) and eight were poor metabolizers for CYP2C19, participated in two studies. Venous blood samples were collected for 24 h after oral ingestion of 40 mg omeprazole with or without 300 mg moclobemide coadministration. The pharmacokinetic change of omeprazole, omeprazole sulphone and 5-hydroxyomeprazole concentrations were assessed to test for an interaction between omeprazole and moclobemide.The coadministration of moclobemide in EMs approximately doubled the mean AUC (from 1834 to 3760 ng ml(-1) h) and C(max) (from 987 to 1649 ng ml(-1)) of omeprazole, and increased the AUC of omeprazole sulphone without changing AUC ratio of omeprazole to omeprazole sulphone. Moclobemide coadministration more than doubled the AUC ratio of omeprazole to 5-hydroxyomeprazole (from 2.5 to 5.3) in EMs, too. There was a significant decrease in Cmax and AUC of 5-hydroxyomeprazole in PMs but no significant changes were seen in the results for omeprazole and omeprazole sulphone AUCs.A single dose of moclobemide resulted in significant suppression of CYP2C19 activity in EMs. We conclude that physicians prescribing moclobemide should pay attention to its pharmacokinetic interactions even on the first day of coadministration with CYP2C19 substrates.