Susumu Nakade

Absolute bioavailability of imidafenacin after oral administration to healthy subjects

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT The absolute bioavailability of imidafenacin in rats and dogs is 5.6% and 36.1%, respectively. The pharmacokinetic profiles of imidafenacin after oral administration have been revealed. Imidafenacin is primarily metabolized to metabolites by CYP3A4 and UGT1A4. WHAT THIS STUDY ADDS The absolute bioavailability of imidafenacin in human is 57.8%. The pharmacokinetic profiles of imidafenacin after intravenous administration are revealed. The formation of metabolites in the plasma is caused mainly by first-pass effects. AIMS To investigate the absolute bioavailability of imidafenacin, a new muscarinic receptor antagonist, a single oral dose of 0.1 mg imidafenacin was compared with an intravenous (i.v.) infusion dose of 0.028 mg of the drug in healthy subjects. METHODS Fourteen healthy male subjects, aged 21-45 years, received a single oral dose of 0.1 mg imidafenacin or an i.v. infusion dose of 0.028 mg imidafenacin over 15 min at two treatment sessions separated by a 1-week wash-out period. Plasma concentrations of imidafenacin and the major metabolites M-2 and imidafenacin-N-glucuronide (N-Glu) were determined. The urinary excretion of imidafenacin was also evaluated. Analytes in biological samples were measured by liquid chromatography tandem mass spectrometry. RESULTS The absolute oral bioavailability of imidafenacin was 57.8% (95% confidence interval 54.1, 61.4) with a total clearance of 29.5 +/- 6.3 l h(-1). The steady-state volume of distribution was 122 +/- 28 l, suggesting that imidafenacin distributes to tissues. Renal clearance after i.v. infusion was 3.44 +/- 1.08 l h(-1), demonstrating that renal clearance plays only a minor role in the elimination of imidafenacin. The ratio of AUC(t) of both M-2 and N-Glu to that of imidafenacin was reduced after i.v. infusion from that seen after oral administration, suggesting that M-2 and N-Glu in plasma after oral administration were generated primarily due to first-pass metabolism. No serious adverse events were reported during the study. CONCLUSIONS The absolute mean oral bioavailability of imidafenacin was determined to be 57.8%. Imidafenacin was well tolerated following both oral administration and i.v. infusion.

Validation and application of a 96-well format solid-phase extraction and liquid chromatography-tandem mass spectrometry method for the quantitation of digoxin in human plasma

To evaluate the pharmacokinetics of digoxin in humans, a sensitive and specific LC/MS/MS method was developed and validated for the determination of digoxin concentrations in human plasma. The method was shown to be more sensitive, specific, accurate, and reproducible than common techniques such as RIA. For detection, a LC/MS/MS system with electro spray ionization tandem mass spectrometry in the positive ion-multiple reaction-monitoring (MRM) mode was used to monitor precursor to product ions of m/z 798.5-51.5 for digoxin and m/z 782.5-35.5 for the internal standard, digitoxin. The method was validated over a concentration range of 0.02-5 ng/mL and was found to have acceptable accuracy, precision, linearity, and selectivity. The mean extraction recovery from spiked plasma samples was above 80%. Imidafenacin, coadministered in a drug-drug interaction study, had no detectable influence on the determination of digoxin in human plasma. The novel method was applied to a drug-drug interaction study of digoxin and imidafenacin and the characterization of steady-state pharmacokinetics of digoxin in humans after oral administration at a dose of 0.25 mg on days 1 and 2 followed by 0.125 mg daily doses on days 3 through 8.

The prediction of human response to ONO-4641, a sphingosine 1-phosphate receptor modulator, from preclinical data based on pharmacokinetic–pharmacodynamic modeling

The pharmacokinetic (PK) and pharmacodynamic (PD) parameters of ONO‐4641 in humans were estimated using preclinical data in order to provide essential information to better design future clinical studies. The characterization of PK/PD was measured in terms of decreased lymphocyte counts in blood after administration of ONO‐4641, a sphingosine 1‐phosphate receptor modulator. Using a two‐compartment model, human PK parameters were estimated from preclinical PK data of cynomolgus monkey and in vitro human metabolism data. To estimate human PD parameters, the relationship between lymphocyte counts and plasma concentrations of ONO‐4641 in cynomolgus monkeys was determined. The relationship between lymphocyte counts and plasma concentrations of ONO‐4641 was described by an indirect‐response model. The indirect‐response model had an Imax value of 0.828 and an IC50 value of 1.29 ng/ml based on the cynomolgus monkey data. These parameters were used to represent human PD parameters for the simulation of lymphocyte counts. Other human PD parameters such as input and output rate constants for lymphocytes were obtained from the literature. Based on these estimated human PK and PD parameters, human lymphocyte counts after administration of ONO‐4641 were simulated. In conclusion, the simulation of human lymphocyte counts based on preclinical data led to the acquisition of useful information for designing future clinical studies. Copyright

Development and validation of an on-line two-dimensional reversed-phase liquid chromatography–tandem mass spectrometry method for the simultaneous determination of prostaglandins E2 and F2α and 13,14-dihydro-15-keto prostaglandin F2α levels in human plasma

We developed and validated an on-line reverse-phase two-dimensional LC/MS/MS (2D-LC/MS/MS) system for simultaneous determination of the levels of prostaglandin (PG) E(2) as well as PGF(2alpha) and its metabolite 13,14-dihydro-15-keto PGF(2alpha) (F(2alpha)-M) in human plasma. Analytes were extracted by a three-step solid-phase extraction. Samples were then analyzed by on-line 2D-LC/MS/MS with electrospray ionization in negative mode. The 2D-LC system is composed of two reverse-phase analytical columns with a trapping column linking the two analytical columns. While an acidic buffer was used for both separation dimensions, differing organic solvents were employed for each dimension: methanol for the first and acetonitrile for the second to increase resolving power. The 2D-LC/MS/MS method was highly selective and sensitive with a significantly lower limit of quantitation (0.5 pg/mL for PGE(2) and 2.5 pg/mL for PGF(2alpha) and F(2alpha)-M, respectively). Linearity of the 2D-LC/MS/MS system was demonstrated for the calibration ranges of 0.5-50 pg/mL for PGE(2) and 2.5-500 pg/mL for PGF(2alpha) and F(2alpha)-M, respectively. Acceptable precision and accuracy were obtained throughout the calibration curve ranges. This highly selective and sensitive method was successfully utilized to determine the endogenous levels of PGE(2), PGF(2alpha), and F(2alpha)-M in plasma samples from six (four male and two female) normal volunteers. The mean concentrations for each analyte were 0.755 pg/mL for PGE(2), 5.70 pg/mL for PGF(2alpha) and 9.48 pg/mL for F(2alpha)-M.

Effect of Itraconazole on the Pharmacokinetics of Imidafenacin in Healthy Subjects

The effect of itraconazole, a potent inhibitor of the CYP3A isoenzyme family, on the pharmacokinetics of imidafenacin, a novel synthetic muscarinic receptor antagonist, was investigated. Twelve healthy subjects participated in this open–label, self‐controlled study. In period I, subjects received a single oral dose of 0.1 mg imidafenacin. In period II, they received multiple oral doses of 200 mg itraconazole for 9 days and a single oral dose of 0.1 mg imidafenacin on day 8. Plasma concentrations of imidafenacin and M‐2, the major metabolite of imidafenacin metabolized by CYP3A4, were determined. Analytes were measured by liquid chromatography tandem mass spectrometry. Following coadministration with itraconazole, the maximum plasma concentration (Cmax) of imidafenacin increased 1.32‐fold (90% confidence intervals [CIs]: 1.12–1.56), and the area under the plasma concentration‐time curve from time 0 to infinity (AUC0‐∞) increased 1.78‐fold (90% CI: 1.47–2.16). In conclusion, itraconazole increases the plasma concentrations of imidafenacin by inhibiting CYP3A4. Therefore, itraconazole or potent CYP3A4 inhibitors should be carefully added to imidafenacin drug regimens.

Impact of pharmacokinetics and pharmacogenetics on the efficacy of pranlukast in Japanese asthmatics

Background and objective:  Wide inter‐individual variability in therapeutic effects limits the efficacy of leukotriene (LT) receptor antagonists in the treatment of asthma. We have reported that genetic variability in the expression of LTC4 synthase is associated with responsiveness to pranlukast in Japanese asthmatic patients. However, the effects of pharmacokinetic variability are less well known. This was an analysis of the pharmacokinetics of pranlukast in a population of adult asthmatics, and its effect on clinical responses. Other factors that may be related to the therapeutic effects of pranlukast, including LTC4 synthase gene polymorphisms, were also investigated.

Target-controlled infusion and population pharmacokinetics of landiolol hydrochloride in patients with peripheral arterial disease

Purpose We previously determined the pharmacokinetic (PK) parameters of landiolol in healthy male volunteers and gynecological patients. In this study, we determined the PK parameters of landiolol in patients with peripheral arterial disease. Methods Eight patients scheduled to undergo peripheral arterial surgery were enrolled in the study. After inducing anesthesia, landiolol hydrochloride was administered at target plasma concentrations of 500 and 1,000 ng/mL for 30 minutes each. A total of 112 data points of plasma concentration were collected from the patients and used for the population PK analysis. A population PK model was developed using a nonlinear mixed-effect modeling software program (NONMEM). Results The patients had markedly decreased heart rates at 2 minutes after initiation of landiolol hydrochloride administration; however, systolic blood pressures were lower than the baseline values at only five time points. The concentration time course of landiolol was best described by a two-compartment model with lag time. The estimates of PK parameters were as follows: total body clearance, 30.7 mL/min/kg; distribution volume of the central compartment, 65.0 mL/kg; intercompartmental clearance, 48.3 mL/min/kg; distribution volume of the peripheral compartment, 54.4 mL/kg; and lag time, 0.633 minutes. The predictive performance of this model was better than that of the previous model. Conclusion The PK parameters of landiolol were best described by a two-compartment model with lag time. Distribution volume of the central compartment and total body clearance of landiolol in patients with peripheral arterial disease were approximately 64% and 84% of those in healthy volunteers, respectively.