Pharmacokinetic/Pharmacodynamic Model of Neutropenia in Real-Life Palbociclib-Treated Patients

Palbociclib is an oral CDK4/6 inhibitor indicated in HR+/HER2- advanced or metastatic breast cancer in combination with hormonotherapy. Its main toxicity is neutropenia. The aim of our study was to describe the kinetics of circulating neutrophils from real-life palbociclib-treated patients. A population pharmacokinetic (popPK) model was first constructed to describe palbociclib pharmacokinetic (PK). Individual PK parameters obtained were then used in the pharmacokinetic/pharmacodynamic (PK/PD) model to depict the relation between palbociclib concentrations and absolute neutrophil counts (ANC). The models were built with a population of 143 patients. Palbociclib samples were routinely collected during therapeutic drug monitoring, whereas ANC were retrospectively retrieved from the patient files. The optimal popPK model was a mono-compartmental model with a first-order absorption constant of 0.187 h−1 and an apparent clearance Cl/F of 57.09 L (32.8% of inter individuality variability (IIV)). The apparent volume of distribution (1580 L) and the lag-time (Tlag: 0.658 h) were fixed to values from the literature. An increase in creatinine clearance and a decrease in alkaline phosphatase led to an increase in palbociclib Cl/F. To describe ANC kinetics during treatment, Friberg’s PK/PD model, with linear drug effect, was used. Parameters estimated were Base (2.92 G/L; 29.6% IIV), Slope (0.0011 L/µg; 28.8% IIV), Mean Transit Time (MTT; 5.29 days; 17.9% IIV) and γ (0.102). The only significant covariate was age on the initial ANC (Base), with lower ANC in younger patients. PK/PD model-based simulations show that the higher the estimated CressSS (trough concentration at steady state), the higher the risk of developing neutropenia. In order to present a risk lower than 20% to developing a grade 4 neutropenia, the patient should show an estimated CressSS lower than 100 µg/L.

Effect of CYP3A4 metabolism on sex differences in the pharmacokinetics and pharmacodynamics of zolpidem

To investigate pharmacokinetic and pharmacodynamic differences of zolpidem between males and females and their causes, including CYP3A4 activity. A single oral dose of zolpidem (10 mg) was administered to 15 male and 15 female healthy subjects. Blood samples were collected up to 12 h post-dose to determine plasma zolpidem concentrations. Pharmacokinetic parameters were obtained using non-compartmental analysis. Digit symbol substitution test, choice reaction time, and visual analog scale of sleepiness were used to evaluate pharmacodynamics. We measured CYP3A4 activity using 4β-hydroxycholesterol, an endogenous metabolite. Mean maximum plasma concentration and area under the plasma concentration–time curve were higher for females than for males (9.9% and 32.5%, respectively); other pharmacokinetic parameters showed no significant differences. Pharmacodynamic scores for females showed delayed recovery compared with that for males. CYP3A4 activity was higher in females than in males (p = 0.030). There was no serious adverse event, and adverse event incidence was not different between the sexes. Zolpidem exposure was about 30% higher in females than in males. Delayed pharmacodynamic score recovery in females could be related to higher zolpidem concentrations. Although apparent clearance was lower in females, systemic clearance might not be the cause of the different exposures to zolpidem.

Moxifloxacin pharmacokinetics, cardiac safety, and dosing for the treatment of rifampicin-resistant tuberculosis in children

Background Moxifloxacin is a priority recommended drug for rifampin-resistant tuberculosis (RR-TB) treatment, but there is limited pediatric pharmacokinetic and safety data, especially in young children. We characterize moxifloxacin population pharmacokinetics, QT-interval prolongation and evaluate optimal dosing in children with RR-TB. Methods Pharmacokinetic data were pooled from two observational studies in South African children 0-17 years of age with RR-TB routinely treated with oral moxifloxacin once daily. The population pharmacokinetics and Fridericia-corrected QT (QTcF)-interval prolongation were characterized in NONMEM. Pharmacokinetic simulations were performed to predict expected exposure and optimal weight-banded dosing. Results Eighty-five children contributed pharmacokinetic data (median [range] age of 4.6 [0.8-15] years); 16 (19%) were <2 years of age, and 8 (9%) were HIV-positive. The median (range) moxifloxacin dose on pharmacokinetic sampling days was 11 mg/kg (6.1 to 17). Apparent clearance was 6.95 L/h for a typical 16 kg child. Stunting and HIV infection increased apparent clearance. Crushed or suspended tablets had faster absorption. The median (range) maximum change in QTcF after moxifloxacin administration was 16.3 (-27.7 to 61.3) ms. No child had QTcF ≥ 500 ms. The concentration-QTcF relationship was nonlinear, with a maximum drug effect (Emax) of 8.80 ms (inter-individual variability = 9.75 ms). Clofazimine use increased Emax by 3.3-fold. Model-based simulations of moxifloxacin pharmacokinetics predicted that current dosing recommendations are too low in children. Conclusions Moxifloxacin doses above 10-15 mg/kg are likely required in young children to match adult exposures but require further safety assessment, especially when co-administered with other QT-prolonging agents.

Cabozantinib (C) exposure-response (ER) analysis for the phase 3 CheckMate 9ER (CM 9ER) trial of nivolumab plus cabozantinib (N+C) versus sunitinib (S) in first-line advanced renal cell carcinoma (1L aRCC).

4561 Background: In the phase 3 CM 9ER trial (NCT03141177), N+C significantly improved progression-free survival (PFS; HR 0.51, 95% CI 0.41–0.64; p < 0.0001), overall survival (OS; HR 0.60, 98.89% CI 0.40–0.89; p = 0.0010), and objective response rate (p < 0.0001) vs S in 1L aRCC (Choueiri, 2020). N+C was generally well tolerated with low rates of treatment-related discontinuations, indicating successful adverse event (AE) management with dose modification to maintain tolerability. Here the impact of C exposure on efficacy and safety outcomes in CM 9ER was evaluated using ER analysis. Methods: Patients (pts, N = 320) with previously untreated aRCC received C 40 mg QD in combination with N 240 mg Q2W; dose reductions of C to 20 mg QD or 20 mg Q2D were allowed to manage AEs. Time-to-event Cox proportional hazard ER models were developed to characterize the relationship between predicted C exposure or apparent clearance (CL/F) and specified endpoints, including PFS, dose modification, and select AEs (palmar-plantar erythrodysesthesia [PPE; Gr ≥1], diarrhea [Gr ≥3], hypertension [Gr ≥3], fatigue/asthenia [Gr ≥3], and ALT/AST elevation [Gr ≥3]). C exposure was defined as the overall average concentration from time zero to the time of event or censoring (CAVG) and estimated by population pharmacokinetic modeling for a typical patient. ER analysis for OS was not done due to the low number of events at the database lock date (March 30, 2020). Results: In the ER analysis of PFS, predicted C exposure at 40-mg and 20-mg QD doses was not significantly associated with the rate of progression or death (HR 1.00, 95% CI 0.78–1.27, for 20-mg vs 40-mg dose). In the ER analysis of AEs, lower predicted C exposure was significantly associated with lower rates of PPE (HR 0.63, 95% CI 0.50–0.78, for 20-mg vs 40-mg dose) and diarrhea (HR 0.48, 95% CI 0.29–0.80) but was not significantly associated with the rates of hypertension, fatigue/asthenia, or ALT/AST elevation. Higher predicted C CL/F was associated with a lower rate of C dose modification; however, this association was not statistically significant (HR 0.80, 95% CI 0.57–1.12, for CL/F 3.2 vs 1.2 L/hr). Conclusions: In ER models of pts with 1L aRCC treated with the combination of N+C, C exposure was not significantly associated with PFS; however, higher C exposure was associated with higher rates of PPE and diarrhea. ER modeling predicts that a starting dose of 40 mg QD C in combination with N with appropriate dose modifications to manage C AEs will not adversely affect the efficacy of the combination in 1L aRCC. Clinical trial information: NCT03141177.

P332 Population pharmacokinetics of ozanimod and active metabolite CC112273 in patients with ulcerative colitis

Background Ozanimod is an oral small molecule sphingosine 1-phosphate receptor modulator approved for relapsing forms of multiple sclerosis (RMS) and under development for ulcerative colitis (UC) and Crohn’s disease (CD). Following multiple dosing of ozanimod in healthy subjects, ozanimod and two of the active metabolites CC112273 and CC1084037 represent approximately 6%, 73%, and 15% of circulating total active drug exposure, respectively. Two separate pharmacokinetic (PK) models were developed for the most prominent metabolite CC112273 and ozanimod. CC1084037 was not modeled due to the high correlation between CC112273 and CC1084037 plasma concentrations. Therefore, this analysis aims to characterise the PK of ozanimod and the major metabolite CC112273 in UC and RMS population. Methods Subjects from 11 studies (Phase 1 to Phase 3) in healthy volunteers, RMS, and UC patients were included in this population PK analysis. The analyses included a total of 18901 concentrations from 2890 subjects for CC112273 and 18834 PK concentrations from 2977 subjects for ozanimod. A 2-compartment model was used to describe the concentration-time profiles of both ozanimod and CC112273, separately. The influence of weight, age, sex, race, disease, or smoking status and hepatic function on the PK of ozanimod and CC112273 were explored. The impact of concomitant corticosteroids on CC112273 PK were evaluated post hoc. Results While the overall apparent clearance of ozanimod was 7% lower in RMS patients compared to UC, similar exposures were observed in both populations. The most influential covariate on ozanimod PK was body weight, with a modest 23% increase in apparent clearance for a 102-kg subject relative to a 70-kg subject (Figure 1). The apparent clearance of CC112273 was 16% greater in RMS patients compared to UC patients, resulting in a slightly higher exposure for UC patients. Increasing body weight had a modest reduction in clearance, while smoking had the largest influence on CC112273 PK of approximately 108% increased clearance (Figure 2). Post-hoc results showed no impact of concomitant prednisone or prednisolone on the PK of CC112273. Other factors, including age, race, sex, or hepatic impairment did not impact the PK of ozanimod or CC112273 PK. Conclusion The population PK model of CC112273 indicates that covariates with the largest effect on CC112273 PK parameters were body weight and smoking status. However, no covariate impacted clearance by more than 25%. The PK of ozanimod and CC112273 were not meaningfully impacted by age including in the elderly, body weight, race, sex, hepatic function, or concomitant prednisone or prednisolone. Overall, the PK of ozanimod and CC112273 were comparable in UC and RMS patients.

Development of a Population Pharmacokinetic Model for Cyclosporine from Therapeutic Drug Monitoring Data

Aim. To develop a population pharmacokinetic model for Uruguayan patients under treatment with cyclosporine (CsA) that can be applied to TDM. Patients and Methods. A total of 53 patients under treatment with CsA were included. 37 patients with at least one pharmacokinetic profile described with four samples were considered for model building, while the remaining 16 were considered for the assessments of predictive performances. Pharmacokinetic parameter estimation was performed using a nonlinear mixed effect modelling implemented in the Monolix® software (version 2019R1, Lixoft, France); meanwhile, simulations were performed in R v.3.6.0 with the mlxR package. Results. A two-compartment model with a first-order disposition model including lag time was used as a structural model. The final model was internally validated using prediction corrected visual predictive check (pcVPC) and other graphical diagnostics. A total of 621 CsA steady-state concentrations were analyzed for model development. Population estimates for the absorption constant (ka) and lag time were 0.523 h-1 and 0.512 h, respectively; apparent clearance (CL/F) was 30.3 L/h ( relative standard error RSE ± 8.25 % ) with an interindividual variability of 39.8% and interoccasion variability of 38.0%; meanwhile, apparent clearance of distribution (Q/F) was 17.0 L/h ( RSE ± 12.1 % ) with and interindividual variability of 53.2%. The covariate analysis identified creatinine clearance (ClCrea) as an individual factor influencing the Cl of CsA. The predictive capacity of the population model was demonstrated to be effective since predictions made for new patients were accurate for C1 and C2 (MPPEs below 50%). Bayesian forecasting improved significantly in the second and third occasions. Conclusion. A population pharmacokinetic model was developed to reasonably estimate the individual cyclosporine clearance for patients. Hence, it can be utilized to individualize CsA doses for prompt and adequate achievement of target blood concentrations of CsA.

Population pharmacokinetics and outcomes of critically ill pediatric patients treated with intravenous colistin at higher than recommended doses

Limited pharmacokinetic (PK) data suggest that currently recommended pediatric dosages of colistimethate sodium (CMS) by the Food and Drug Administration and European Medicines Agency may lead to suboptimal exposure, resulting in plasma colistin concentrations frequently <2 mg/L. We conducted a population PK study in 17 critically ill patients 3 months-13.75 years (median 3.3 years) old, who received CMS for infections caused by carbapenem-resistant Gram-negative bacteria. CMS was dosed at 200,000 IU/kg/d [6.6 mg colistin base activity (CBA)/kg/d, 6 patients], 300,000 IU/kg/d (9.9 mg CBA/kg/d, 10 patients) and 350,000 IU/kg/d (11.6 mg CBA/kg/d, 1 patient). Plasma colistin concentrations were determined using ultra-performance liquid chromatography combined with electrospray ionization tandem mass spectrometry. Colistin PK was described by a one-compartment disposition model including creatinine clearance, body weight and the presence or absence of systemic inflammatory response syndrome (SIRS) as covariates (p<0.05 for each). The average colistin plasma steady-state concentration (Css,avg) ranged from 1.11-8.47 mg/L (median 2.92 mg/L). Ten patients had Css,avg ≥2 mg/L. The presence of SIRS was associated with decreased apparent clearance of colistin (47.8% of that without SIRS). The relationship between the mg/day of CBA to achieve each 1 mg/L of plasma colistin Css,avg and creatinine clearance (mL/min) was described by linear regression with different slopes for patients with and without SIRS. Nephrotoxicity, probably colistin-unrelated, was observed in one patient. In conclusion, administration of CMS at the above doses improved exposure and was well tolerated. Apparent clearance of colistin was influenced by creatinine clearance and the presence or absence of SIRS.

Population Pharmacokinetics of Palbociclib in aReal-World Situation

Palbociclib is an oral cyclin-dependent kinase inhibitor that is used in combination with aromatase inhibitors in the treatment of postmenopausal women with metastatic breast cancer. Its metabolism profile is associated with an important interpatient variability. We performed a population pharmacokinetics study of palbociclib in women routinely followed in a cancer center. One hundred and fifty-one samples were analyzed. The sampling times after administration ranged from 0.9 to 75 h and the samples were taken between 1 and 21 days after the beginning of the palbociclib cycle. Palbociclib was determined using a validated mass spectrometry method. The best model that described the concentrations was a one-compartment model with first-order absorption and an absorption lag time. Interindividual variability could only be estimated on the clearance and the first-order absorption. Creatinine clearance was found to be a significant covariate for the apparent clearance. No significant covariates could be observed with the first-order absorption. First-order absorption and absorption lag times were difficult to assess because of the constraints linked to the real-world setting due to the small number of samples used during the absorption process. However, palbociclib apparent clearance was satisfactorily estimated. Population pharmacokinetics (POP PK) with palbociclib could help to optimize dosing.

Only Modest Effect of Lipids and Albumin on Apparent Mycophenolic Acid Clearance in Pediatric Transplant Recipients – a Retrospective Cohort Study

Background: There is growing evidence for the need of therapeutic drug monitoring (TDM) of the active compound Mycophenolic Acid (MPA) of mycophenolate mofetil therapy for the management of antirejection therapy after pediatric renal transplantation. While there is substantial inter- and intra-patient variability of MPA exposure, the factors affecting its apparent clearance (CL/F) are understudied. The objective of this study was to determine the relationship between MPA CL/F, eGFR, creatinine, Cystatin C, triglycerides, cholesterol and albumin. Material and Methods: We calculated 1004 estimated mass-spectrometry-determined MPA CL/F using trough concentrations from 35 pediatric renal transplant patients. Results: Mean age was 8.7±4.6 years at transplant with a median follow-up of 5.8 years. Each patient had a median of 30 MPA trough concentrations. The median MPA AUC was 53.21 mg*h/L, the median CL/F was 8.66 L/h. Univariate and multivariate analysis revealed significant correlations of CL/F with creatinine, triglycerides, cholesterol and albumin, and very weakly with hemoglobin, whereas cystatin C was unrelated. Especially higher lipid levels and weekly, but significantly, lower albumin augmented CL/F. However, the correlations were not strong enough to predict CL/F. Conclusion: The data presented indicate the necessity for MPA TDM and suggest that dose modifications may apply in the face of low serum albumin and hyperlipidemia.

Scutellarin is Highly Likely to be Responsible for Drug-Drug Interactions Mediated by Hepatic Organic Anion-Transporting Polypeptide1B3

Purpose Scutellarin, a flavonoid derived from the plant Erigeron breviscapus, is currently widely used to treat cerebrovascular diseases, liver-related diseases, and hyperlipidemia in china and other East Asian countries. This study was to investigate the effect of scutellarin on the uptake of rosuvastatin in HEK293T cells expressing human organic anion transporting polypeptide 1B3 (hOATP1B3) and rat OATP1B2 (rOATP1B2), respectively, and the effect of scutellarin on the pharmacokinetics of rosuvastatin in rats. Methods The newly established HEK293T cells expressing hOATP1B3 and rOATP1B2 were used to examine the effects of scutellarin and positive controls on in vitro rosuvastatin transport. After co-feeding with scutellarin, the rosuvastatin area under the plasma concentration-time curve (AUC0–24h), the peak plasma drug concentration (Cmax), elimination half-life (t1/2), time to reach Cmax (tmax), clearance (CL) and apparent clearance (CL/F) of rosuvastatin were determined in rats. Results Scutellarin inhibited hOATP1B3- and rOATP1B2-mediated rosuvastatin uptake (IC50: 45.54 ± 6.67 μM and 27.58 ± 3.97 μM) in vitro in a concentration-dependent manner. After co-feeding with scutellarin, the AUC0–24h and Cmax of rosuvastatin in rats increased to 27.4% and 37.7%, respectively. The t1/2 and tmax of rosuvastatin showed no significant change. Moreover, scutellarin caused 29.2% and 28.1% decrease in the CL and CL/F of rosuvastatin. Conclusion Scutellarin may inhibit the hOATP1B3- and rOATP1B2-mediated transport of rosuvastatin in vitro, and exerts a moderate inhibitory effect on the pharmacokinetics of rosuvastatin in rats. Scutellarin is highly likely to participate in drug-drug interactions, as mediated by OATP1B3 in humans.