A Population Pharmacokinetic Study to Compare a Novel Empagliflozin L-Proline Formulation with Its Conventional Formulation in Healthy Subjects

Empagliflozin is a sodium-glucose cotransporter 2 (SGLT2) inhibitor that is commonly used for the treatment of type 2 diabetes mellitus (T2DM). CKD-370 was newly developed as a cocrystal formulation of empagliflozin with co-former L-proline, which has been confirmed to be bioequivalent in South Korea. This study aimed to quantify the differences in the absorption phase and pharmacokinetic (PK) parameters of two empagliflozin formulations in healthy subjects by using population PK analysis. The plasma concentration data of empagliflozin were obtained from two randomized, open-label, crossover, phase 1 clinical studies in healthy Korean subjects after a single-dose administration. A population PK model was constructed by using a nonlinear mixed-effects (NLME) approach (Monolix Suite 2021R1). Interindividual variability (IIV) and interoccasion variability (IOV) were investigated. The final model was evaluated by goodness-of-fit (GOF) diagnostic plots, visual predictive checks (VPCs), prediction errors, and bootstrapping. The PK of empagliflozin was adequately described with a two-compartment combined transit compartment model with first-order absorption and elimination. Log-transformed body weight significantly influenced systemic clearance (CL) and the volume of distribution in the peripheral compartment (V2) of empagliflozin. GOF plots, VPCs, prediction errors, and the bootstrapping of the final model suggested that the proposed model was adequate and robust, with good precision at different dose strengths. The cocrystal form did not affect the absorption phase of the drug, and the PK parameters were not affected by the different treatments.

Meropenem pharmacokinetic/pharmacodynamic target attainment and clinical response in ICU patients: A prospective observational study

BACKGROUND

Several studies report lack of meropenem pharmacokinetic/pharmacodynamic (PK/PD) target attainment (TA) and risk of therapeutic failure with intermittent bolus infusions in intensive care unit (ICU) patients. The aim of this study was to describe meropenem TA in an ICU population and the clinical response in the first 72 h after therapy initiation.

METHODS

A prospective observational study of ICU patients ≥18 years was conducted from 2014 to 2017. Patients with normal renal clearance (NRC) and augmented renal clearance (ARC) and patients on continuous renal replacement therapy (CRRT) were included. Meropenem was administered as intermittent bolus infusions, mainly at a dose of 1 g q6h. Peak, mid, and trough levels were sampled at 24, 48, and 72 h after therapy initiation. TA was defined as 100% T > 4× MIC or trough concentration above 4× MIC. Meropenem PK was estimated using traditional calculation methods and population pharmacokinetic modeling (P-metrics®). Clinical response was evaluated by change in C-reactive protein (CRP), Sequential Organ Failure Assessment (SOFA) score, leukocyte count, and defervescence.

RESULTS

Eighty-seven patients were included, with a median Simplified Acute Physiology (SAPS) II score 37 and 90 days mortality rate of 32%. Median TA was 100% for all groups except for the ARC group with 45.5%. Median CRP fell from 175 (interquartile range [IQR], 88-257) to 70 (IQR, 30-114) (p < .001) in the total population. A reduction in SOFA score was observed only in the non-CRRT groups (p < .001).

CONCLUSION

Intermittent meropenem bolus infusion q6h gives satisfactory TA in an ICU population with variable renal function and CRRT modality, except for ARC patients. No consistent relationship between TA and clinical endpoints were observed.

Is Gender an Important Factor in the Precision Medicine Approach to Levocetirizine?

Currently, there is insufficient information on the variability in levocetirizine pharmacometrics among individuals, a crucial aspect for establishing its clinical use. The gender differences in pharmacokinetics and the extent of variation in pharmacodynamics have not been definitively identified. The primary goal of this study was to investigate gender differences in levocetirizine pharmacokinetics and quantitatively predict and compare how these gender-related pharmacokinetic differences impact pharmacodynamics, using population pharmacokinetic-pharmacodynamic modeling. Bioequivalence results for levocetirizine (only from the control formulation) were obtained from both healthy Korean men and women. Physiological and biochemical parameters for each individual were utilized as pharmacokinetic comparison and modeling data between genders. Pharmacodynamic modeling was performed using reported data on antihistamine responses following levocetirizine exposure. Gender, weight, body surface area, peripheral distribution volume, albumin, central-peripheral inter-compartmental clearance, and the fifth sequential absorption rate constant were explored as effective covariates. A comparison of the model simulation results showed a higher maximum concentration and faster plasma loss in females than in males, resulting in a faster recovery to baseline of the antihistamine effect; however, the absolute differences between genders in the mean values were not large within 10 ng/mL (for plasma concentrations) or % (wheal and flare size changes). Regarding the pharmacokinetics and pharmacodynamics of levocetirizine, the gender effect may not be significant when applying the usual dosage (5 mg/day). This study will be useful for bridging the knowledge gap in scientific precision medicine by introducing previously unconfirmed information regarding gender differences in levocetirizine pharmacometrics.

Optimizing anidulafungin exposure across a wide adult body size range

Echinocandins like anidulafungin are first-line therapies for candidemia and invasive candidiasis, but their dosing may be suboptimal in obese patients. Our objective was to quantify anidulafungin exposure in a cohort of adults across a wide body size range to test if body size affects anidulafungin pharmacokinetics (PK). We enrolled 20 adults between the ages of 18 and 80 years, with an equal distribution of patients above and below a body mass index of 30 kg/m2. A single 100-mg dose of anidulafungin was administered, followed by intensive sampling over 72 h. Population PK analysis was used to identify and compare covariates of anidulafungin PK parameters. Monte Carlo simulations were performed to compute the probability of target attainment (PTA) based on alternative dosing regimens. Participants (45% males) had a median (range) age of 45 (21-78) years and a median (range) weight of 82.7 (42.4-208.3) kg. The observed median (range) of AUC0-∞ was 106.4 (51.9, 138.4) mg∙h/L. Lean body weight (LBW) and adjusted body weight (AdjBW) were more influential than weight as covariates of anidulafungin PK parameters. The conventional 100 mg daily maintenance is predicted to have a PTA below 90% in adults with an LBW > 55 kg or an AdjBW > 75 kg. A daily maintenance dose of 150-200 mg is predicted in these heavier adults. Anidulafungin AUC0-∞ declines with increasing body size. A higher maintenance dose will increase the PTA compared to the current approach in obese patients.

Exploring Differences in Pharmacometrics of Rabeprazole between Genders via Population Pharmacokinetic-Pharmacodynamic Modeling

Rabeprazole is a proton pump inhibitor that inhibits gastric acid production and increases gastric pH; it is widely used clinically as a treatment option for gastritis and gastric ulcers. However, information on the inter-individual variability of rabeprazole pharmacometrics, which is a key element in establishing its scientific clinical use, is still lacking. Particularly, the differences in pharmacokinetics between genders and the degree of variation in pharmacodynamics have not been clearly identified. Thus, the main purpose of this study was to explore any differences in rabeprazole pharmacokinetics between genders and to quantitatively predict and compare the effects of any differences in pharmacokinetics between genders on known pharmacodynamics using population pharmacokinetic-pharmacodynamic modeling. To compare pharmacokinetics and modeling data between genders, bioequivalence results were used simultaneously on healthy Korean men and women using the physiological and biochemical parameters derived from each individual. Pharmacodynamic modeling was performed based on the data of previously reported gastric pH changes in response to rabeprazole plasma concentrations, which was co-linked to the central compartmental bioavailable concentration in the population pharmacokinetic model. There was no significant difference in the level of rabeprazole exposure and elimination of plasma between genders following oral administration of 10 mg enteric-coated rabeprazole tablets; however, there was a clear delay in absorption in women compared to men. Additionally, a comparison of pharmacokinetic parameters normalized to body weight between genders showed that the maximum plasma concentrations were significantly higher in women than in men, again suggesting gender differences in rabeprazole absorption. The population pharmacokinetic profiles for rabeprazole were described using a three-sequential multi-absorption with lag time (Tlag) two-compartment model, whereas body surface area and gender were explored as effective covariates for absorption rate constant and Tlag, respectively. The effect of increased gastric pH due to plasma exposure to rabeprazole was explained using the Sigmoid Emax model, with the baseline as a direct response. The significantly longer rabeprazole Tlag in females delayed the onset of an effect by an average of 1.58 times (2.02-3.20 h), yet the overall and maximum effects did not cause a significant difference within 15%. In the relative comparison of the overall efficacy of rabeprazole enteric-coated tablet administration between genders, it was predicted based on the model that males would have higher efficacy. This study will be very useful in broadening the perspective of interpreting drug diversity between individuals and narrowing the gap in knowledge related to scientific precision medicine by presenting new information on gender differences in rabeprazole pharmacometrics that had not been previously identified.

Clinical trial simulation to evaluate tenofovir disoproxil fumarate/emtricitabine HIV pre-exposure prophylaxis dosing during pregnancy

Objective

To evaluate upward-adjustment of tenofovir disoproxil fumarate (TDF)/emtricitabine (FTC) pre-exposure prophylaxis (PrEP) dosing during pregnancy in order to maintain target plasma concentrations associated with HIV protection.

Design

Population pharmacokinetic (PK) modeling and clinical trial simulation (CTS).

Material and methods

We developed population pharmacokinetic models for TFV and FTC using data from the Partners Demonstration Project and a PK study of TDF/FTC among cisgender women by Coleman et al., and performed an in-silico simulation. Pregnancy-trimester was identified as a significant covariate on apparent clearance in the optimized final model. We simulated 1,000 pregnant individuals starting standard daily oral TDF/FTC (300 mg/200 mg) prior to pregnancy. Upon becoming pregnant, simulated patients were split into two study arms: one continuing standard-dose and the other receiving double standard-dose throughout pregnancy.

Results

Standard-dose trough TFV concentrations were significantly lower in pregnancy compared to pre-pregnancy, with 34.0%, 43.8%, and 65.1% of trough plasma concentrations below the lower bound of expected trough concentrations presumed to be the protective threshold in the 1st, 2nd, and 3rd trimesters, respectively. By comparison, in the simulated double-dose group, 10.7%, 14.4%, and 27.8% of trough concentrations fell below the estimated protective thresholds in the 1st, 2nd, and 3rd trimesters, respectively. The FTC trough plasma concentration during pregnancy was also lower than pre-pregnancy, with 45.2% of the steady-state trough concentrations below the estimated protective trough concentrations of FTC. In the pregnancy-adjusted double-dose group, 24.1% of trough plasma concentrations were lower than protective levels.

Conclusions

Our simulation shows >50% of research participants on standard dosing would have 3rd trimester trough plasma TFV concentrations below levels associated with protection. This simulation provides the quantitative basis for the design of prospective TDF/FTC studies during pregnancy to evaluate the safety and appropriateness of pregnancy-adjusted dosing.

Population pharmacokinetic-pharmacodynamic analysis of givinostat

BACKGROUND

Givinostat (ITF2357), an oral, synthetic histone deacetylase inhibitor, significantly improved all histological muscle biopsy parameters in a Phase II study in boys with Duchenne muscular dystrophy (DMD).

RESEARCH DESIGN AND METHODS

A population pharmacokinetic (PK) model, including seven clinical studies, was developed to explore the effect of covariates on givinostat PK. The final model was qualified to simulate pediatric dosing recommendations. A PK/pharmacodynamic (PD) model was developed to simulate the link between givinostat plasma concentration and platelet time course in 10-70-kg children following 6 months of givinostat 20-70 mg twice daily.

RESULTS

A two-compartment model, with first-order input with lag and first-order elimination from the central compartment, described givinostat PK, demonstrating increasing apparent clearance with increasing body weight. The PK/PD model well-described platelet count time course. Weight-based dosing (arithmetic mean systemic exposure of 554-641 ng·h/mL) produced an average platelet count decrease from baseline of 45% with maximum decrease within 28 days. After 1 week and 6 months, ~1% and ~14-15% of patients, respectively, had a platelet count <75 × 10⁹/L.

CONCLUSIONS

Based on these data, givinostat dosing will be body weight adjusted and include monitoring of platelet counts to support efficacy and safety in a Phase III DMD study.

Population Pharmacokinetic Modeling of Zaltoprofen in Healthy Adults: Exploring the Dosage Regimen

Zaltoprofen is a drug used for various pain and inflammatory diseases. Scientific and quantitative dosage regimen studies regarding its clinical application are scarce. This study aimed to discover effective covariates related to interindividual pharmacokinetic variability through population pharmacokinetic modeling for zaltoprofen and to explore dosage regimens. The bioequivalence results of healthy Korean males, biochemical analysis, and CYP2C9 genotyping information were utilized in modeling. The established model has been sufficiently verified through a bootstrap, goodness-of-fit, visual predictive check, and normalized prediction distribution error. External data sets derived from the literature were used for further model validation. The final model could be used to verify the dosage regimen through multiple exposure simulations according to the numerical change of the selected covariates. Zaltoprofen pharmacokinetics could be explained by a two-compartment with a first-order absorption model. Creatinine clearance (CrCL) and albumin were identified as effective covariates related to interindividual zaltoprofen pharmacokinetic variability, and they had positive and negative correlations with clearance (CL/F), respectively. The differences in pharmacokinetics between individuals according to CYP2C9 genetic polymorphisms (*1/*1 and *1/*3) were not significant or valid covariates. The model simulation confirmed that zaltoprofen pharmacokinetics could significantly differ as the CrCL and albumin levels changed within the normal range. Steady-state plasma exposure to zaltoprofen was significantly reduced in the group with CrCL and albumin levels of 130 mL/min and 3.5 g/dL, respectively, suggesting that dose adjustment may be necessary. This study is useful to guide precision medicine of zaltoprofen and provides scientific quantitative judgment data for its clinical applications.

Leveraging in vitro and pharmacokinetic models to support bench to bedside investigation of XTMAB-16 as a novel pulmonary sarcoidosis treatment

Background: Sarcoidosis is a chronic, multisystem inflammatory disorder characterized by non-caseating epithelioid granulomas; infiltration of mononuclear cells; and destruction of microarchitecture in the skin, eye, heart, and central nervous system, and the lung in >90% of cases. XTMAB-16 is a chimeric anti-tumor necrosis factor alpha (TNFα) antibody, distinct from other anti-TNF antibodies based on its molecular structure. The efficacy of XTMAB-16 has not been clinically demonstrated, and it is still undergoing clinical development as a potential treatment for sarcoidosis. The current study demonstrates the activity of XTMAB-16 in a well-established in vitro sarcoidosis granuloma model, although XTMAB-16 is not yet approved by the United States Food and Drug Administration (FDA) for treatment of sarcoidosis, or any other disease. Objective: To provide data to guide safe and efficacious dose selection for the ongoing clinical development of XTMAB-16 as a potential treatment for sarcoidosis. Methods: First, XTMAB-16 activity was evaluated in an established in vitro model of granuloma formation using peripheral blood mononuclear cells from patients with active pulmonary sarcoidosis to determine a potentially efficacious dose range. Second, data obtained from the first-in-human study of XTMAB-16 (NCT04971395) were used to develop a population pharmacokinetic (PPK) model to characterize the pharmacokinetics (PK) of XTMAB-16. Model simulations were performed to evaluate the sources of PK variability and to predict interstitial lung exposure based on concentrations in the in vitro granuloma model. Results: XTMAB-16 dose levels of 2 and 4 mg/kg, once every 2 weeks (Q2W) or once every 4 weeks (Q4W) for up to 12 weeks, were supported by data from the non-clinical, in vitro secondary pharmacology; the Phase 1 clinical study; and the PPK model developed to guide dose level and frequency assumptions. XTMAB-16 inhibited granuloma formation and suppressed interleukin-1β (IL-1β) secretion in the in vitro granuloma model with a half maximal inhibitory concentration (IC₅₀) of 5.2 and 3.5 μg/mL, respectively. Interstitial lung concentrations on average, following 2 or 4 mg/kg administered Q2W or Q4W, are anticipated to exceed the in vitro IC₅₀ concentrations. Conclusion: The data presented in this report provide a rationale for dose selection and support the continued clinical development of XTMAB-16 for patients with pulmonary sarcoidosis.

Evaluating and Improving Neonatal Gentamicin Pharmacokinetic Models Using Aggregated Routine Clinical Care Data

Model-informed precision dosing (MIPD) can aid dose decision-making for drugs such as gentamicin that have high inter-individual variability, a narrow therapeutic window, and a high risk of exposure-related adverse events. However, MIPD in neonates is challenging due to their dynamic development and maturation and by the need to minimize blood sampling due to low blood volume. Here, we investigate the ability of six published neonatal gentamicin population pharmacokinetic models to predict gentamicin concentrations in routine therapeutic drug monitoring from nine sites in the United State (n = 475 patients). We find that four out of six models predicted with acceptable levels of error and bias for clinical use. These models included known important covariates for gentamicin PK, showed little bias in prediction residuals over covariate ranges, and were developed on patient populations with similar covariate distributions as the one assessed here. These four models were refit using the published parameters as informative Bayesian priors or without priors in a continuous learning process. We find that refit models generally reduce error and bias on a held-out validation data set, but that informative prior use is not uniformly advantageous. Our work informs clinicians implementing MIPD of gentamicin in neonates, as well as pharmacometricians developing or improving PK models for use in MIPD.

Parametric and Nonparametric Population Pharmacokinetic Models to Assess Probability of Target Attainment of Imipenem Concentrations in Critically Ill Patients

Population pharmacokinetic modeling and simulation (M&S) are used to improve antibiotic dosing. Little is known about the differences in parametric and nonparametric M&S. Our objectives were to compare (1) the external validation of parametric and nonparametric models of imipenem in critically ill patients and (2) the probability of target attainment (PTA) calculations using simulations of both models. The M&S software used was NONMEM 7.2 (parametric) and Pmetrics 1.5.2 (nonparametric). The external predictive performance of both models was adequate for eGFRs ≥ 78 mL/min but insufficient for lower eGFRs, indicating that the models (developed using a population with eGFR ≥ 60 mL/min) could not be extrapolated to lower eGFRs. Simulations were performed for three dosing regimens and three eGFRs (90, 120, 150 mL/min). Fifty percent of the PTA results were similar for both models, while for the other 50% the nonparametric model resulted in lower MICs. This was explained by a higher estimated between-subject variability of the nonparametric model. Simulations indicated that 1000 mg q6h is suitable to reach MICs of 2 mg/L for eGFRs of 90-120 mL/min. For MICs of 4 mg/L and for higher eGFRs, dosing recommendations are missing due to largely different PTA values per model. The consequences of the different modeling approaches in clinical practice should be further investigated.

Semimechanistic Population Pharmacokinetic Modeling to Investigate Amyloid Beta Trafficking and Accumulation at the BBB Endothelium

Elevated exposure to toxic amyloid beta (Aβ) peptides and consequent blood-brain barrier (BBB) dysfunction are believed to promote vasculopathy in Alzheimer's disease (AD). However, the accumulation kinetics of different Aβ isoforms within the BBB endothelium and how it drives BBB dysfunction are not clearly characterized. Using single positron emission computed tomography (SPECT)-computed tomography (CT) dynamic imaging coupled with population pharmacokinetic modeling, we investigated the accumulation kinetics of Aβ40 and Aβ42 in the BBB endothelium. Brain clearance was quantified after intracerebral administration of ¹²⁵I-Aβ, and BBB-mediated transport was shown to account for 54% of ¹²⁵I-Aβ40 total clearance. A brain influx study demonstrated lower values of both maximal rate (V_max) and Michaelis constant (K_m) for ¹²⁵I-Aβ42 compared to ¹²⁵I-Aβ40. Validated by a transcytosis study in polarized human BBB endothelial cell (hCMEC/D3) monolayers, model simulations demonstrated impaired exocytosis was responsible for inefficient permeability and enhanced accumulation of Aβ42 in the BBB endothelium. Further, both isoforms were shown to disrupt the exocytosis machinery of BBB endothelial cells so that a vicious cycle could be generated. The validated model was able to capture changes in Aβ steady-state levels in plasma as well as the brain during AD progression and allowed us to predict the kinetics of Aβ accumulation in the BBB endothelium.

Pharmacokinetic Comparison between Methotrexate-Loaded Nanoparticles and Nanoemulsions as Hard- and Soft-Type Nanoformulations: A Population Pharmacokinetic Modeling Approach

The purpose of this study was to identify and explore the differences in pharmacokinetics between different nanoformulations. This was done by comparing the pharmacokinetics of methotrexate-loaded nanoparticles [poly(lactic-co-glycolic acid); size of 163.70 ± 10.25 nm] and nanoemulsions (olive oil and Labrasol; size of 173.77 ± 5.76 nm), which represent hard- and soft-type nanoformulations, respectively. In addition, the population pharmacokinetic modeling approach as a useful tool for the comparison of pharmacokinetics between nanoformulations was newly proposed through this study. Significant pharmacokinetic differences were identified between nanoformulations through the new population pharmacokinetic modeling approach. As a result, the formulation type was explored as a significant covariate. The clearance and bioavailability of methotrexate-loaded nanoemulsions tended to decrease by 99% and increase by 19%, respectively, compared to those of the nanoparticles. The exploration of significant pharmacokinetic differences between drug formulations and their correlations presented in this study provide new perspectives on the development of nanoformulations.

Aminoglycosides in the Intensive Care Unit: What Is New in Population PK Modeling?

Background: Although aminoglycosides are often used as treatment for Gram-negative infections, optimal dosing regimens remain unclear, especially in ICU patients. This is due to a large between- and within-subject variability in the aminoglycoside pharmacokinetics in this population. Objective: This review provides comprehensive data on the pharmacokinetics of aminoglycosides in patients hospitalized in the ICU by summarizing all published PopPK models in ICU patients for amikacin, gentamicin, and tobramycin. The objective was to determine the presence of a consensus on the structural model used, significant covariates included, and therapeutic targets considered during dosing regimen simulations. Method: A literature search was conducted in the Medline/PubMed database, using the terms: ‘amikacin’, ‘gentamicin’, ‘tobramycin’, ‘pharmacokinetic(s)’, ‘nonlinear mixed effect’, ‘population’, ‘intensive care’, and ‘critically ill’. Results: Nineteen articles were retained where amikacin, gentamicin, and tobramycin pharmacokinetics were described in six, 11, and five models, respectively. A two-compartment model was used to describe amikacin and tobramycin pharmacokinetics, whereas a one-compartment model majorly described gentamicin pharmacokinetics. The most recurrent significant covariates were renal clearance and bodyweight. Across all aminoglycosides, mean interindividual variability in clearance and volume of distribution were 41.6% and 22.0%, respectively. A common consensus for an optimal dosing regimen for each aminoglycoside was not reached. Conclusions: This review showed models developed for amikacin, from 2015 until now, and for gentamicin and tobramycin from the past decades. Despite the growing challenges of external evaluation, the latter should be more considered during model development. Further research including new covariates, additional simulated dosing regimens, and external validation should be considered to better understand aminoglycoside pharmacokinetics in ICU patients.

Matrix Effects of the Hydroethanolic Extract of Calyces of Physalis peruviana L. on Rutin Pharmacokinetics in Wistar Rats Using Population Modeling

Rutin is the rutinose conjugate of quercetin. It presents several biological activities and is the major flavonoid in the hydroalcoholic extract of the calyces of Physalis peruviana L. It also shows hypoglycemic activity after oral administration. The aim of this work was to study the matrix effects of the extract from P. peruviana calyces on the pharmacokinetics of rutin and its metabolites in Wistar rats, using non-compartmental and population pharmacokinetic analyses. A pharmacokinetic study was performed after intravenous and oral administration of different doses of pure rutin and the extract. In the non-compartmental analysis, it was found that rutin from the extract exhibited higher distribution and clearance, as well as an 11-fold increase in the bioavailability of its active metabolites. A population pharmacokinetic model was also carried out with two compartments, double absorption and linear elimination, in which the extract and the doses were the covariates involved. This model correctly described the differences observed between rutin as a pure compound and rutin from the extract, including the dose dependency.

A Population Pharmacokinetic Model of (R)- and (S-) Oxybutynin and Its Active Metabolites After Oral and Intravesical Administration to Healthy Volunteers

Oxybutynin is a racemic anticholinergic drug used for the symptomatic treatment of detrusor overactivity. The formation of active metabolites related to tolerability problems depends on the route of administration. The objective of this evaluation was to develop a pharmacokinetic model for oral/intravesical administration as the basis for simulations with different dosages. Data from a published changeover clinical study with 18 healthy adults receiving a single oral dose of 5 mg immediate-release oxybutynin and single and multiple intravesical doses of 10 mg oxybutynin solution was evaluated. Enantioselective plasma concentrations of oxybutynin and N-desethyloxybutynin (NDO) were used to establish a population pharmacokinetic model using nonlinear mixed-effects modeling with NONMEM 7.4.1. For both enantiomers, the data were described well by a 2-compartment model for oxybutynin with an additional compartment for NDO. Oxybutynin absorption was modeled by transit compartments for oral and first-order absorption for intravesical application. Bioavailability of the more active (R)-enantiomer was 7% for oral and 10%-22% for intravesical administration. In simulations, intravesical doses of 5 to 15 mg (R)-oxybutynin administered 2 to 3 times daily decreased peak-trough fluctuations of NDO to 8% compared with 24% after oral administration. The NDO/oxybutynin ratio was reduced from 17 after oral administration to unity. Chronic intravesical versus oral administration of (R)-oxybutynin generates distinctly lower and less variable concentrations of (R)-NDO. Pharmacokinetic simulations suggest that exposure for 12.5 mg (R)-oxybutynin administered twice daily might not compromise efficacy and tolerability compared with exposure for standard thrice-daily administrations. This assumption needs to be assessed in clinical studies.

Hydroxychloroquine in Coronavirus Disease 2019 Patients: What Still Needs to Be Known About the Kinetics

Different dosage regimens of hydroxychloroquine are used to manage COVID-19 patients, without information on the pharmacokinetics in this population.Blood samples (n=101) were collected from 57 COVID-19 patients for 7 days and concentrations were compared with simulated kinetic profiles.Hydroxychloroquine exposure is low and cannot be predicted by other populations.

Physiologically Relevant In Vitro-In Vivo Correlation (IVIVC) Approach for Sildenafil with Site-Dependent Dissolution

This study aimed to establish a physiologically relevant in vitro-in vivo correlation (IVIVC) model reflecting site-dependent dissolution kinetics for sildenafil based on population-pharmacokinetic (POP-PK) modeling. An immediate release (IR, 20 mg) and three sustained release (SR, 60 mg) sildenafil tablets were prepared by wet granulation method. In vitro dissolutions were determined by the paddle method at pH 1.2, 4.5, and 6.8 media. The in vivo pharmacokinetics were assessed after oral administration of the prepared IR and SR formulations to Beagle dogs (n = 12). The dissolution of sildenafil from SR formulations was incomplete at pH 6.8, which was not observed at pH 1.2 and pH 4.5. The relative bioavailability was reduced with the decrease of the dissolution rate. Moreover, secondary peaks were observed in the plasma concentration-time curves, which may result from site-dependent dissolution. Thus, a POP-PK model was developed to reflect the site-dependent dissolution by separately describing the dissolution and absorption processes, which allowed for estimation of the in vivo dissolution of sildenafil. Finally, an IVIVC was established and validated by correlating the in vitro and in vivo dissolution rates. The present approach may be applied to establish IVIVC for various drugs with complex dissolution kinetics for the development of new formulations.

Alterations in Pharmacokinetics of Gemcitabine and Erlotinib by Concurrent Administration of Hyangsayukgunja-Tang, a Gastroprotective Herbal Medicine

Gemcitabine and erlotinib are the chemotherapeutic agents used in the treatment of various cancers and their combination is being accepted as a first-line treatment of advanced pancreatic cancer. Hyangsayukgunja-tang (HYT) is a traditional oriental medicine used in various digestive disorders and potentially helpful to treat gastrointestinal adverse effects related to chemotherapy. The present study was aimed to evaluate the effect of HYT on the pharmacokinetics of gemcitabine and erlotinib given simultaneously in rats. Rats were pretreated with HYT at an oral dose of 1200 mg/kg/day once daily for a single day or 14 consecutive days. Immediately after pretreatment with HYT, gemcitabine and erlotinib were administered by intravenous injection (10 mg/kg) and oral administration (20 mg/kg), respectively. The effects of HYT on pharmacokinetics of the two drugs were estimated by non-compartmental analysis and pharmacokinetic modeling. The pharmacokinetics of gemcitabine and erlotinib were not altered by single dose HYT pretreatment. However, the plasma levels of OSI-420 and OSI-413, active metabolites of erlotinib, were significantly decreased in the multiple dose HYT pretreatment group. The pharmacokinetic model estimated increased systemic clearances of OSI-420 and OSI-413 by multiple doses of HYT. These data suggest that HYT may affect the elimination of OSI-420 and OSI-413.

Magnitude of Increased Infliximab Clearance Imposed by Anti-infliximab Antibodies in Crohn's Disease Is Determined by Their Concentration

Antibodies (Abs) against infliximab (IFX) increase IFX clearance and can result in treatment failure and acute hypersensitivity reactions. However, interpretation of their clinical value is complicated by individual differences in Ab responses and methods used for quantification. The increase in IFX clearance imposed by anti-IFX Abs has generally been evaluated using a binary classification, i.e., positive or negative. This analysis aimed to investigate if anti-IFX Ab concentrations provide a more adequate prediction of alterations in clearance. Data originated from a clinical trial on Crohn's disease patients with IFX treatment failure. The trial was not originally designed for pharmacokinetic analysis. Therefore, published pharmacokinetic models were utilized as priors to enable covariate investigation. The impact of anti-IFX Abs on clearance was assessed using different mathematical relationships and exploiting information from two different quantification assays, measuring semi-quantitative "total" or "unbound neutralizing" concentrations of anti-IFX Ab, respectively. Inclusion of anti-IFX Ab status/concentration improved the model's performance for all investigated relationships. The anti-IFX Ab concentrations were superior to the binary classifications, indicating that the magnitude of increase in IFX clearance imposed by anti-IFX Abs closely relates to their concentration. Furthermore, total anti-IFX Ab concentrations appeared superior to the unbound neutralizing fraction in identifying high clearance individuals. Simulations showed that even at low concentrations, anti-IFX Abs lead to sub-therapeutic IFX concentrations, supporting a need of treatment interventions in all anti-IFX Ab positive patients. The developed model can serve as a basis for further investigations to refine treatment recommendations for patients with anti-IFX Abs.