Retraction Note to: Identification of CYP3A4 as the primary cytochrome P450 responsible for the metabolism of tandospirone by human liver microsomes The publisher has retracted this article [1] because it is an incorrect version that was published in error: Figures 5 and 6 are missing.

Current Understanding of the Equivalence Evaluations for In Vitro Tests on Generic Dry Powder Inhaler Drug Products in Japan Abstract The Japanese Ministry of Health, Labour and Welfare issued the basic principles for bioequivalence evaluations of generic dry powder inhaler (DPI) drug products in 2016. This document presents the recommendations of the methodology for the effective development of generic DPI drug products. Based on this document, the Pharmaceuticals and Medical Devices Agency (PMDA) advises the efficient development in the consultation meeting with generic companies. The PMDA generally requires the data of in vitro tests, pharmacokinetics studies, and clinical endpoint studies for generic development. In vitro tests play a critical role in the development of the generic versions because these tests are used to predict the efficacy and safety of other populations on whom clinical endpoint studies have not been conducted. We are aware that some points need further discussion, such as the recommendations for at least four groups of stages (group 1: the induction port and pre-separator, group 2: greater than 5 μm, group 3: ranging from 3 to 5 μm, group 4: ranging from 0.8 to 3 μm) for in vitro tests of the generic DPI products. This article shows the current understanding and recommendations with respect to in vitro tests, particularly for at least four groups of stages.

Acknowledgement to Referees

Drug–Drug Interaction Potential of Darolutamide: In Vitro and Clinical Studies Abstract Background and Objectives Darolutamide is a novel androgen receptor (AR) antagonist approved for the treatment of nonmetastatic castration-resistant prostate cancer (nmCRPC). Accordingly, the drug–drug interaction (DDI) potential of darolutamide was investigated in both nonclinical and clinical studies. Methods In vitro studies were performed to determine the potential for darolutamide to be a substrate, inducer or inhibitor for cytochrome P450 (CYP) isoforms, other metabolizing enzymes and drug transporters. A phase I drug-interaction study in healthy volunteers evaluated the impact of co-administering rifampicin [CYP3A4 and P-glycoprotein (P-gp) inducer] and itraconazole [CYP3A4, P-gp and breast cancer resistance protein (BCRP) inhibitor] on the pharmacokinetics of darolutamide. Two further phase I studies assessed the impact of co-administering oral darolutamide on the pharmacokinetics of midazolam (sensitive CYP3A4 substrate) and dabigatran etexilate (P-gp substrate) and the impact on the pharmacokinetics of co-administered rosuvastatin [a substrate for BCRP, organic anion-transporting polypeptide (OATP)1B1, OATP1B3 and organic anion transporter (OAT)3]. Results In vitro, darolutamide was predominantly metabolized via oxidative biotransformation catalyzed by CYP3A4 and was identified as a substrate for P-gp and BCRP. The enzymatic activity of nine CYP isoforms was not inhibited or slightly inhibited in vitro with darolutamide, and a rank order and mechanistic static assessment indicated that risk of clinically relevant DDIs via CYP inhibition is very low. In vitro, darolutamide exhibited no relevant induction of CYP1A2 or CYP2B6 activity. Inhibition of BCRP-, P-gp-, OAT3-, MATE1-, MATE2-K-, OATP1B1- and OATP1B3-mediated transport was observed in vitro. Phase I data showed that darolutamide exposure increased 1.75-fold with co-administered itraconazole and decreased by 72% with rifampicin. Co-administration of darolutamide with CYP3A4/P-gp substrates showed no effect or only minor effects. Rosuvastatin exposure increased 5.2-fold with darolutamide because of BCRP and probably also OATPB1/OATPB3 inhibition. Conclusions Darolutamide has a low potential for clinically relevant DDIs with drugs that are substrates for CYP or P-gp; increased exposure of BCRP and probably OATP substrates was the main interaction of note.

Inhibition of Rat CYP1A2 and CYP2C11 by Honokiol, a Component of Traditional Chinese Medicine Abstract Background and Objectives Honokiol, a major constituent isolated from Magnolia officinalis, is regarded as a phytochemical marker and bioactive substance present in many traditional Chinese medicines. However, the effect of honokiol on cytochrome P450 (CYP) has not been thoroughly investigated. The aim of this study was to investigate the effect of honokiol on CYP1A2 and CYP2C11 in vitro and in vivo. Methods The effect of honokiol on CYP1A2 and CYP2C11 was investigated with rat liver microsomes (RLMs) by measuring phenacetin and tolbutamide metabolism (probe drugs for CYP1A2 and CYP2C11, respectively), and then explored in vivo by measuring the effect of honokiol (2.5 and 5 mg/kg, intravenous injection) on the pharmacokinetics of theophylline and tolbutamide (probe drugs for CYP1A2 and CYP2C11, respectively) in rats in vivo. Results Honokiol inhibited the formation of acetaminophen from phenacetin and 4-hydroxytolbutamide from tolbutamide in RLMs, with inhibition constant (Ki) values of 1.6 μM and 16.5 μM, respectively. In vivo, honokiol (2.5 or 5.0 mg/kg) increased the half-life (t1/2) of theophylline by 40.9% and 119.9%, decreased the clearance (CL) by 23.8% and 42.9%, and increased the area under the curve (AUC) by 41.3% and 83.4%, respectively. Similarly, the t1/2 of tolbutamide increased by 25.5% and 33.8%, the CL decreased by 14.3% and 19.1%, and the AUC increased by 19.2% and 25.7%, respectively. Conclusion The inhibition of CYP1A2 by honokiol is greater than the inhibition of CYP2C11. The changes in the pharmacokinetics of theophylline and tolbutamide in rats treated with honokiol are due to the inhibition of CYP1A2 and CYP2C11 activity in a dose-dependent manner.

The Effects of CYP3A5 Genetic Polymorphisms on Serum Tacrolimus Dose-Adjusted Concentrations and Long-Term Prognosis in Chinese Heart Transplantation Recipients Abstract Background and Objectives Effective management of immunosuppressants is extemely important to improve prognosis of heart transplant recipients. We aim to investigate the effects of cytochrome P450 (CYP) 3A5 (rs776746) single nucleotide polymorphisms (SNPs) on serum tacrolimus concentrations/doses (C/Ds, ng/mL per mg/kg) and long-term prognosis in Chinese heart transplant recipients. Methods We detected the CYP3A5 SNPs of 203 consecutive Chinese heart transplant recipients between August 2005 and July 2012, and 55 of them who received tacrolimus-based immunosuppressive therapy were enrolled in this study. The tacrolimus C/Ds at 1, 3, 6, 12, 24 and 36 months after transplantation were routinely calculated. X-ray-guided endomyocardial biopsies (EMBs) were performed at 1, 3 and 6 months after heart transplantion to evaluate acute rejection degrees. All participants were then followed up annually until May 2018. The designed primary endpoint was all-cause mortality. Results In 55 heart transplant recipients (43 males and 12 females), CYP3A5 non-expressors (CYP3A5*3/*3, n = 40) had significantly higher tacrolimus C/Ds than expressors (CYP3A5*1/*3, n = 15) at all time points (P < 0.001). Chi-squared test showed no significant differences in EMB-proven acute rejections between the two groups within 6 months after heart transplantion. The median follow-up period was 94.7 months, and eight patients died. Kaplan–Meier analysis showed CYP3A5 expressors tend to have higher mortality than non-expressors (20% vs 12.5%, log-rank: P = 0.314). Conclusions CYP3A5 SNPs affect tacrolimus pharmacokinetics in Chinese heart transplant recipients, and non-expressors have higher tacrolimus C/Ds. In addition, expressors tend to have a worse long-term prognosis than non-expressors.

Clinical Pharmacokinetics of Vancomycin in Critically Ill Children Abstract Background and Objective Critically ill children exhibit altered pharmacokinetic parameters of vancomycin, mainly due to altered renal excretion and volume of distribution (as a result of altered plasma protein concentrations). We assessed the pharmacokinetic parameters of vancomycin in this subpopulation. Methods Vancomycin trough concentrations in critically ill children were obtained following first dose and at steady state. Using a one-compartment model, clearance (CL), volume of distribution (Vd), elimination half-life (t1/2), and area under the time–concentration curve for 24 h (AUC0–24) were estimated. Subgroup analyses were carried out, with patients differentiated based on age, renal clearance, outcome, and renal dysfunction. Protein-free vancomycin concentrations were calculated using a previously reported formula. Results Twenty-two samples were evaluated for first-dose and 182 for steady-state pharmacokinetics, and similar pharmacokinetic parameter values were observed at first dose and at steady state. Only 36.4% and 47.3% of the samples attained the recommended AUC0–24 (mg·hr/L) of > 400 at first dose and at steady state, while 62.5% of the patients with renal dysfunction achieved this target. Nearly 40% of the patients had augmented renal clearance (ARC), which was associated with higher CL, shorter t1/2, and lower AUC values. Amongst the patients with ARC, none had AUC0–24 (mg·hr/L) > 400 at first dose, while 16% achieved this target at steady state. Volume of distribution was significantly higher in infants and a decreasing trend was observed in toddlers, children, and older children at steady state. Children with renal dysfunction had lower CL, prolonged t1/2, and higher AUC values than patients with normal renal clearance at first dose. A good correlation was observed between trough concentration and AUC0–24, as corroborated by the area under the receiver operating characteristic curve. The median fraction of protein-free vancomycin was around 77%. Conclusion Vancomycin dosing strategies in younger children should be revisited, and increased doses should be considered for critically ill children with ARC in order to achieve therapeutic concentrations of AUC0–24.

Vancomycin Pharmacokinetics in Patients with Advanced Cancer Near End of Life Abstract Background and Objective The effect of cancer cachexia on the pharmacokinetics of vancomycin remains unclear. We investigated whether the pharmacokinetics of vancomycin and the risk of kidney injury are altered with the development of cancer cachexia. Methods A retrospective analysis was conducted using therapeutic drug monitoring data obtained from 86 cancer patients who received vancomycin intravenously for infection. The patients were classified into four groups according to the stage of cachexia defined by international consensus—non-cachexia (n = 26), pre-cachexia (n = 10), cachexia (n = 21) and refractory cachexia (n = 29). Vancomycin pharmacokinetics were analyzed by a traditional one-compartment model and Bayesian method using plasma concentrations measured in these patients. Renal function and pharmacokinetic parameters were compared between the non-cachexia patients (n = 26) and total cancer cachexia patients (n = 60). Result No significant difference in estimated glomerular filtration rate was observed between the non-cachexia and the total cancer cachexia patients. In contrast, systemic clearance of vancomycin was significantly lower in the total cancer cachexia patients compared with the non-cachexia patients when analyzed by the traditional one-compartment model [median (range)—49.7 (9.8‒98.7) vs 70.2 (12.5‒211.8) mL/min, p < 0.01] and by the Bayesian method [45.6 (12.5–84.7) vs 63.3 (12.2–102.5) mL/min, p < 0.05]. None of the non-cachexia patients developed kidney injury, whereas 15% (9 of 60 patients) of the total cancer cachexia patients developed kidney injuries (p = 0.052). Conclusions The present study revealed that cancer patients with cachexia may have reduced vancomycin clearance compared with those without cachexia. Cancer cachexia may be a risk factor of vancomycin-associated kidney injury, independent of renal function.

Effects of Animal Strain, Dose, and Cotreatment with Saikosaponin b 2 on the Pharmacokinetics of Saikosaponin a in Rats Abstract Background and Objectives Radix Bupleuri (RB, Chaihu in Chinese) has been used as a traditional medicine for more than 2000 years in China, Japan, Korea, and other Asian countries. Saikosaponin a (SSa), the most abundant saikosaponin in RB, exhibits various pharmacological activities, including anti-inflammatory, antitumor, antiviral, immunoregulatory, neuromodulatory, and hepatoprotective activities. A comprehensive study of the pharmacokinetic characteristics of SSa is needed to gain a detailed understanding of its pharmacodynamic mechanism. Methods Here, we determined the effects of rat strain (Sprague Dawley and Wistar), oral dose, and cotreatment with saikosaponin b2 (SSb2) on the pharmacokinetics of SSa by measuring SSa in plasma via LC–MS/MS. Results The results showed that the absorption of SSa in Wistar rats was statistically superior to its absorption in Sprague Dawley rats based on pharmacokinetic parameters such as the area under the concentration–time curve (AUC0–t) and the peak concentration (Cmax). Pharmacokinetic studies of different doses of SSa in Wistar rats revealed that the systemic exposure of SSa, based on AUC values, increased disproportionately with dose, indicating that SSa exhibits non-dose-proportional pharmacokinetics. In addition, our studies showed that SSb2, a characteristic component of vinegar-baked Radix Bupleuri (VBRB), inhibits the absorption of SSa in rats. Conclusions The pharmacokinetic data for SSa obtained in this study will play an important role in attempts to better understand the fate of SSa in rats and to explore how these saikosaponins are likely to exert their pharmacological effects in vivo. In addition, further research is needed to elucidate the interactions of saikosaponins with metabolic enzymes and transporters in order to account for the phenomena observed in this study.

Further Assessment of the Relay Hepatocyte Assay for Determination of Intrinsic Clearance of Slowly Metabolised Compounds Using Radioactivity Monitoring and LC–MS Methods Abstract Background and Objectives Low-clearance drugs are widely used by industry mostly because of their often longer half-life, allowing for lower or less frequent dosing. Nevertheless, prediction of human clearance for these molecules from in vitro models presents a great challenge for pharmaceutical scientists. The objective of this study was to further characterise the predictive accuracy of the relay hepatocyte assay using 14C and 3H labelled proprietary compounds with a low extraction ratio and the known clearance mechanism in rats. Highly permeable compounds cleared by metabolism as well as rate limitation by transport were included in this study. Methods Blood clearance was determined from concentration–time profiles following intravenous dosing to rats. In vitro clearance was determined from the single concentration parent depletion-time profiles throughout the incubation period of up to 20 h (five relays) using radioactivity monitoring in tandem with mass spectrometry. A new approach was proposed to correct concentrations for loss and dilution during the relay steps. Clearance was predicted with a standard well-stirred model for the liver and predicted values were then compared with observed data to evaluate method accuracy. Results The results showed that intrinsic clearance values predicted using the relay hepatocyte assay from either radioactivity or mass spectrometry concentration data were comparable. A significant difference in prediction accuracy between the permeable compounds cleared by hepatic metabolism (about 2-fold) and the compound that was the hepatic uptake substrate (5- to 6-fold of actual) was demonstrated. Conclusions The relay method is effective in predicting in vivo clearance for the compounds that are cleared via hepatic metabolism but tends to be notably underpredictive for drugs that rely on uptake transport. Consistent with the overall trend toward underprediction of hepatic clearance from the in vitro models prevalently used in the pharmaceutical industry, all values predicted from the hepatocyte relay method were lower than observed.