Population pharmacokinetics of mizoribine in pediatric patients with kidney disease.

BACKGROUND: The present study aimed to obtain information enabling optimisation of the clinical effect of mizoribine (MZR) in pediatric patients with kidney disease. METHODS: A total of 105 pediatric patients with kidney disease treated at our institutions were enrolled. Kidney transplant patients were excluded. Population pharmacokinetic analysis of MZR was performed based on serum concentration data. Area under the curve from time zero to infinity (AUC∞) and maximal concentration (C max) were calculated by Bayesian analysis. RESULTS: In children, the appearance of MZR in the blood tended to be slower and the subsequent rise in blood concentration tended to be more sluggish, compared to healthy adults. Apparent volume of distribution and oral clearance were also higher in children compared to adults. A significant positive correlation was observed between patient age and AUC∞. There were significant differences of AUC∞ and C max by age group. No relationship was observed between the administration method of MZR and serum concentration. CONCLUSION: The pharmacokinetics of MZR was different in children compared to adults. To obtain the expected clinical efficacy, the regular MZR dosage schedule (2-3 mg/kg/day) might be insufficient for pediatric patients. In particular, younger patients might require a higher dosage of MZR per unit body weight.

Membrane transport mechanisms of quinidine and procainamide in renal LLC-PK1 and intestinal LS180 cells.

The aim of the present study was to compare the membrane transport mechanisms of procainamide with those of quinidine using renal epithelial LLC-PK(1) and intestinal epithelial LS180 cells. In LLC-PK(1) cells, the transcellular transport of 10 microM quinidine in the basolateral-to-apical direction was similar to that in the opposite direction, and 1 mM tetraethylammonium (TEA) did not affect the transcellular transport of the drug. On the other hand, the transcellular transport of 10 microM TEA and procainamide in LLC-PK(1) cells was directional from the basolateral side to the apical side. In addition, this directional transcellular transport of procainamide was diminished in the presence of 1 mM TEA. In LS180 cells, the temperature-dependent cellular uptake of 100 microM quinidine and procainamide was markedly increased by alkalization of the apical medium, and was inhibited significantly by 1 mM several hydrophobic cationic drugs, but not by TEA. The rank order of the inhibitory effects of hydrophobic cationic drugs on the uptake of procainamide in LS180 cells was imipramine>quinidine>diphenhydramine asymptotically equal topyrilamine>procainamide, which was consistent with that on the uptake of quinidine. These findings suggested that procainamide (but not quinidine) was transported by cation transport systems in renal epithelial cells, but that both procainamide and quinidine were taken up by another cation transport system in intestinal epithelial cells.

Evaluation of limited sampling designs to estimate maximal concentration and area under the curve of mizoribine in pediatric patients with renal disease.

The aim of this study was to evaluate limited sampling designs to estimate the maximal concentration (C(max)) and area under the curve (AUC) of mizoribine in pediatric patients with renal disease. We utilized 48 serum mizoribine concentration profiles obtained from the full (6-point) sampling pharmacokinetic test, and estimated 48 individual C(max) and AUC values accurately with Bayesian analysis using the full sampling data. We then developed limited sampling models (LSM) for C(max) and AUC using 1-4 serum mizoribine concentration data points. The C(max) and AUC estimation performance of the Bayesian and LSM analysis was fairly good in the 3-point (2, 3, and 6 hr after the dose) sampling design. In addition, the C(max) estimation performance of the Bayesian and LSM analysis deteriorated only marginally even in the 1-point (3 hr) sampling design. On the other hand, the AUC estimation performance seemed to be inadequate in the 1-point (3 hr) sampling design; however, it improved markedly in the 2-point (3 and 6 hr) sampling design. These findings suggested that the 1-point (3 hr) sampling design is promising for approximate C(max) estimation, but that the 2-point (3 and 6 hr) sampling design is preferable to estimate the AUC of mizoribine.

Membrane transport mechanisms of mizoribine in the rat intestine and human epithelial LS180 cells.

The aim of the present study was to characterize membrane transport mechanisms of mizoribine in the intestinal epithelial cells. We evaluated the contribution of Na(+)-dependent and -independent membrane transporters to mizoribine absorption in the rat intestine using an in situ closed loop method. In addition, we evaluated the effects of structurally related compounds, extracellular Na(+) concentrations, and an inhibitor of Na(+)-independent equilibrative nucleoside transporter, nitrobenzylmercaptopurine ribonucleoside (NBMPR), on the uptake of mizoribine in human intestinal epithelial LS180 cells. In the presence and also absence of Na(+) in rat intestinal loops, more than 60% of the administered dose (50 microg at the concentration of 100 microg/ml=386 microM) of mizoribine was absorbed in 40 min. In the LS180 cells, ribavirin and inosine reduced the uptake of 400 microM mizoribine with the increasing concentrations (from 5 to 50 mM) of the inhibitors. The cellular uptake of mizoribine in the absence of extracellular Na(+) decreased to 72.7% of the uptake in the presence of extracellular Na(+), whereas 100 microM NBMPR decreased the uptake of mizoribine markedly to 34.7% of that without NBMPR. These findings suggest that Na(+)-independent nucleoside transporters are largely responsible for absorption of mizoribine in the intestine.

Additional notes on clinical repeated-dose pharmacokinetic trials applying a peak-and-trough sampling design to estimate oral clearance.

In the previous study, we performed a simulation of a clinical pharmacokinetic trial, in which blood was sampled at two time points corresponding to the peak concentration (C(peak)) and trough concentration (C(trough)) following repetitive oral administration at the dose, D, and dosing interval, tau. The approximate oral clearance (CL/F(approx)), estimated as 2 x D/(C(peak) x tau+C(trough) x tau), is accurate for drugs with an elimination half-life comparative to or longer than tau; however, it was suggested that we might not use CL/F(approx) for drugs with a considerably short elimination half-life relative to tau. In the present study, we evaluated the accuracy of the alternative oral clearance (CL/F(exp)) estimated by the simple monoexponential model. In contrast to CL/F(approx), CL/F(exp) was accurate for drugs with a short elimination half-life relative to tau. The present finding in conjunction with our previous study suggested that the peak-and-trough sampling design is promising for the clinical repeated-dose pharmacokinetic trial for drugs with not only slow but also rapid elimination from the body. We think that the accuracy and precision of the two analysis methods to estimate oral clearance (CL/F(approx) and CL/F(exp)) for a target drug should be evaluated carefully before and after a real clinical trial.

Directional transcellular transport of bisoprolol in P-glycoprotein-expressed LLC-GA5-COL150 cells, but not in renal epithelial LLC-PK1 Cells.

To evaluate the mechanism responsible for the tubular secretion of bisoprolol, we compared transcellular transport of bisoprolol with that of tetraethylammonium (TEA), cimetidine, and quinidine across LLC-PK1 cell monolayers grown on porous membrane filters. TEA and cimetidine were actively transported in the basolateral-to-apical direction by the specific transport system. Pharmacokinetic analysis indicated that basolateral influx and apical efflux were cooperatively responsible for the directional transport of TEA and cimetidine. Lipophilic cationic drugs, quinidine, S-nicotine, and bisoprolol, significantly diminished basolateral influx and apical efflux clearance of cimetidine. However, transcellular transport of quinidine in the basolateral-to-apical direction was similar to that in the opposite direction in LLC-PK1 cells. In contrast, quinidine was transported actively in the basolateral-to-apical direction in P-glycoprotein-expressed LLC-GA5-COL150 cells. Pharmacokinetic analysis indicated that P-glycoprotein increased the apical efflux of quinidine and also decreased the apical influx of the drug. Basolateral-to-apical transport of bisoprolol was also similar to apical-to-basolateral transport in LLC-PK1 cells, whereas the drug was directionally transported from the basolateral to the apical side in LLC-GA5-COL150 cells. These results suggested that bisoprolol was not significantly transported via transport systems involved in the directional transport of TEA and cimetidine, but that P-glycoprotein was responsible for the directional transport of bisoprolol as well as quinidine in renal epithelial cells.

Contribution of Na+-independent nucleoside transport to ribavirin uptake in the rat intestine and human epithelial LS180 cells.

The aim of the present study was to characterize the intestinal absorption of ribavirin (1-beta-d-ribofuranosyl-1, 2, 4-trizole-3-carboxamide). We evaluated the contribution of Na(+)-dependent and -independent transport to ribavirin absorption in the rat intestine using an in situ closed loop method. In addition, we performed pharmacokinetic analysis of the uptake of ribavirin in human intestinal epithelial LS180 cells, and also evaluated the effect of extracellular Na(+) concentration and an inhibitor of the Na(+)-independent equilibrative nucleoside transporter, nitrobenzylmercaptopurine ribonucleoside (NBMPR), on the uptake of ribavirin in the cells. In the presence and also absence of Na(+) in rat intestinal loops, more than 80% of the administered dose (50 microg at a concentration of 100 microg/ml=409 microM) of ribavirin was absorbed in 40 min. The absorption of ribavirin in the rat intestine was significantly reduced by coadministration of 10 mg/ml (=37.3 mM) inosine. In LS180 cells, 100 microM ribavirin was taken up time-dependently, and the influx clearance of the drug was similar to the efflux clearance. Five mM inosine and mizoribine reduced the uptake of 100 microM ribavirin in LS180 cells. The absence of extracellular Na(+) decreased the uptake of 100 microM ribavirin only weakly in the cells, whereas the uptake of 100 microM-2 mM ribavirin was markedly decreased by 100 microM NBMPR. These findings suggested that Na(+)-independent nucleoside transport contributes significantly to intestinal absorption of ribavirin at relatively high concentrations (>or=100 microM).

The apical uptake transporter of levofloxacin is distinct from the peptide transporter in human intestinal epithelial Caco-2 cells.

The aim of this study was to investigate the involvement of the peptide transporter for absorption of levofloxacin in Caco-2 cells. To evaluate the activity of apical and basolateral peptide transport, we first performed pharmacokinetic analysis of transcellular transport of glycylsarcosine (Gly-Sar) in cell monolayers grown on porous membrane filters. Transcellular transport of Gly-Sar at the medium pH 6 was greater in the apical-to-basolateral direction than in the opposite direction. Influx clearance of Gly-Sar at the apical membrane was much greater than basolateral influx and efflux clearance, indicating that the apical peptide transporter plays an important role in directional transcellular transport of the dipeptide across Caco-2 cell monolayers. We then evaluated the effect of various compounds on the uptake of Gly-Sar and levofloxacin at the apical membrane of Caco-2 cells. The apical uptake of [3H]Gly-Sar was significantly inhibited by Ala-Ala, Gly-Sar, and also levofloxacin, whereas that of [14C]levofloxacin was not inhibited by Ala-Ala and Gly-Sar. On the other hand, the apical uptake of [14C]levofloxacin was inhibited by nicotine, enalapril, fexofenadine, and L-carnitine. These findings indicated that the apical uptake transporter of levofloxacin is distinct from the peptide transporter in Caco-2 cells.

Pharmacokinetic analysis of transcellular transport of levofloxacin across LLC-PK1 and Caco-2 cell monolayers.

To characterize the membrane transport responsible for the renal excretion and intestinal absorption of levofloxacin, we performed pharmacokinetic analysis of transcellular transport across LLC-PK(1) and Caco-2 cell monolayers. Transcellular transport of levofloxacin in LLC-PK(1) cells was greater in the basolateral-to-apical direction than in the opposite direction. Pharmacokinetic analysis indicated that basolateral uptake was the direction-determining step for the transcellular transport of levofloxacin in LLC-PK(1) cells. The apical efflux clearance of levofloxacin in LLC-PK(1) cells was increased at the medium pH 6 as compared with at pH 8, suggesting that membrane transport characteristics of levofloxacin are apparently similar to those of a prototypical organic cation, tetraethylammonium. On the other hand, transcellular transport of levofloxacin in Caco-2 cells was only slightly greater in the basolateral-to-apical direction than in the opposite direction. The apical efflux clearance of levofloxacin in Caco-2 cells was greater than basolateral efflux clearance, and apical influx clearance was greater than any other membrane transport clearance. In addition, the apical uptake of levofloxacin as well as quinidine in Caco-2 cells was inhibited significantly by nicotine and imipramine. The findings indicated that some transporters are responsible not only for the efflux but also for the influx of levofloxacin at the apical membrane of Caco-2 cells.

Nonlinear mixed effects model analysis of the pharmacokinetics of aripiprazole in healthy Japanese males.

The population pharmacokinetic parameters of aripiprazole in healthy Japanese males were estimated using a nonlinear mixed effects model (NONMEM) program. Pharmacokinetic data for population analysis were obtained from the single-dose (24 subjects), multiple-dose (15 subjects), and itraconazole-coadministration (27 subjects) trials. The time course of plasma aripiprazole concentration following oral administration was well described by a two-compartment model with first-order input. The mean values of the absorption lag time (ALAG) and absorption rate constant (KA) were estimated to be 0.805 h and 2.65 h(-1), respectively. The mean volume of the central (V(1)/F) and peripheral (V(2)/F) compartment was 3.84 and 1.54 l/kg, respectively, and the mean value of inter-compartment clearance (Q/F) was 0.168 l/h/kg. Oral clearance (CL/F) was estimated to be 0.0645 l/h/kg in the group with CYP2D6*1/*1, *1/*2 and *2/*2. The decrease in CL/F was estimated to be 0.0135 l/h/kg in the group with CYP2D6*1/*5, *1/*10, *2/*5, *2/*10, and *2/*41, and 0.0293 l/h/kg in the group with CYP2D6*5/*10, *10/*10, and *41/*41. The plasma concentration of aripiprazole was increased by coadministration of itraconazole, and the decrease in CL/F was estimated to be 0.0181 l/h/kg.

Pharmacokinetic analysis of transcellular transport of quinidine across monolayers of human intestinal epithelial Caco-2 cells.

To investigate the mechanism responsible for the intestinal absorption of a lipophilic organic cation, quinidine, we performed a pharmacokinetic analysis of transcellular transport across Caco-2 cell monolayers grown on a porous membrane. Basolateral-to-apical transport of the drug was almost constant in the concentration range of 100 nM-100 microM. Transcellular transport was greater in the apical-to-basolateral direction than in the opposite direction. Apical-to-basolateral transport was greater at a concentration of 100 microM than 100 nM. The calculated influx clearance value of the apical membrane was much greater than the other influx/efflux clearance values of cell membranes, and was 5.6-fold the influx clearance value of the basolateral membrane at the drug concentration of 100 microM. We also investigated the uptake of quinidine at the apical membrane of Caco-2 cells grown on plastic dishes. The uptake was markedly increased by alkalization of the apical medium at 37 degrees C, and was decreased at low temperature (4 degrees C). In addition, it was inhibited by diphenhydramine and levofloxacin, but not by carvedilol, rifamycin SV, or L-carnitine. These findings indicated that the influx at the apical membrane was the direction-determining step in the transcellular transport of quinidine across Caco-2 cell monolayers, and that some specific transport system was involved in this influx.