Apixaban for Prevention of Thromboembolism in Pediatric Heart Disease

BACKGROUND

Children with heart disease frequently require anticoagulation for thromboprophylaxis. Current standard of care (SOC), vitamin K antagonists or low-molecular-weight heparin, has significant disadvantages.

OBJECTIVES

The authors sought to describe safety, pharmacokinetics (PK), pharmacodynamics, and efficacy of apixaban, an oral, direct factor Xa inhibitor, for prevention of thromboembolism in children with congenital or acquired heart disease.

METHODS

Phase 2, open-label trial in children (ages, 28 days to <18 years) with heart disease requiring thromboprophylaxis. Randomization 2:1 apixaban or SOC for 1 year with intention-to-treat analysis.

PRIMARY ENDPOINT

a composite of adjudicated major or clinically relevant nonmajor bleeding. Secondary endpoints: PK, pharmacodynamics, quality of life, and exploration of efficacy.

RESULTS

From 2017 to 2021, 192 participants were randomized, 129 apixaban and 63 SOC. Diagnoses included single ventricle (74%), Kawasaki disease (14%), and other heart disease (12%). One apixaban participant (0.8%) and 3 with SOC (4.8%) had major or clinically relevant nonmajor bleeding (% difference -4.0 [95% CI: -12.8 to 0.8]). Apixaban incidence rate for all bleeding events was nearly twice the rate of SOC (100.0 vs 58.2 per 100 person-years), driven by 12 participants with ≥4 minor bleeding events. No thromboembolic events or deaths occurred in either arm. Apixaban pediatric PK steady-state exposures were consistent with adult levels.

CONCLUSIONS

In this pediatric multinational, randomized trial, bleeding and thromboembolism were infrequent on apixaban and SOC. Apixaban PK data correlated well with adult trials that demonstrated efficacy. These results support the use of apixaban as an alternative to SOC for thromboprophylaxis in pediatric heart disease. (A Study of the Safety and Pharmacokinetics of Apixaban Versus Vitamin K Antagonist [VKA] or Low Molecular Weight Heparin [LMWH] in Pediatric Subjects With Congenital or Acquired Heart Disease Requiring Anticoagulation; NCT02981472).

Understanding the Role of Pharmacometrics-Based Clinical Decision Support Systems in Pediatric Patient Management: A Case Study Using Lyv Software

Pharmacometrics could play a key role in shifting pediatric pharmacotherapy from dosing for an average patient to individualizing dosing. Clinicians can have these quantitative tools at their disposal without requiring significant training through the development of clinical decision support systems with easy-to-use interfaces that have a back-end analysis engine or pharmacometric model that uses extensive electronic health record data to predict an individualized dose for each patient. There has been increased development of these clinical decision support systems recently, and for these tools to make the proper breakthrough into clinical practice, it is of utmost importance to perform rigorous testing to ensure adequate predictive performance. In this article, we walk through the components of a decision support tool and the testing required to determine its robustness using an example of a decision support tool we developed for vancomycin dosing in pediatrics.

Abstract PS17-08: Population pharmacokinetic and exposure-response modeling of the oral selective estrogen receptor degrader, rintodestrant (G1T48), in patients with ER+/HER2- advanced breast cancer

Background: Rintodestrant is an orally bioavailable, potent and selective estrogen receptor degrader (SERD) that competitively binds to the estrogen receptor (ER) and blocks ER signaling in tumors resistant to other endocrine therapies. Clinical trials have been conducted to evaluate the safety and efficacy of rintodestrant in healthy volunteers and patients with ER+/HER2- locally advanced or metastatic breast cancer (ABC). Population pharmacokinetic (PK) and exposure-response (Ex/Re) analyses were performed to further characterize the PK profile of rintodestrant and identify potential Ex/Re relationships. Methods: The present analyses include data from two studies: (1) G1T48-01, a Phase 1 first-in-human study of rintodestrant monotherapy (200-1000 mg once daily [QD]) in women with ER+/HER2- ABC after progression on endocrine therapy (NCT03455270), and (2) G1T48-10, a study in healthy volunteers investigating potential drug-drug interactions between rintodestrant (200 mg QD) and palbociclib (125 mg QD). A PK model was developed using nonlinear mixed effects methodology to estimate PK parameters for individual patients. A tumor dynamic model was built to characterize the relationship between rintodestrant concentrations and the longitudinal tumor sizes according to RECIST v1.1. Ex/Re for key pharmacodynamic markers, including ER target engagement (18F-fluoroestradiol positron emission tomography [FES-PET]), dynamics of cell-free DNA mutational burden, ER degradation and proliferation (Ki67) in tumors, and enumeration of circulating tumor cells are being evaluated. Relationships between model-predicted exposures and study endpoints (objective response rate, clinical benefit rate) are also being evaluated. Results: Rintodestrant PK was best described using a linear two-compartment model with a mixed absorption model. The predicted population mean trough concentration of rintodestrant at the recommended Phase 2 dose (800 mg QD) exceeded the IC90 value for ER degradation established in vitro. A positive Ex/Re relationship was identified between total exposure and target ER engagement as measured by FES-PET. A clear Ex/Re relationship was not identified between any PK parameters and ER degradation or proliferation, potentially due to confounding effects from covariates in the model (eg, prior SERD treatment, ESR1 mutations, etc). Additional exploration of these covariates is ongoing. The final PK, Ex/Re and PK/tumor dynamics model results will be presented. Conclusions: A population PK model was developed and Ex/Re relationship analyses were performed to support the development of rintodestrant for the treatment of patients with ER+ breast cancer. Initial results identified an Ex/Re relationship with target ER engagement via FES-PET analysis.

Citation Format: Andrew P Beelen, Chao Li, Praneeth Jarugula, Mathangi Gopalakrishnan, Jessica A Sorrentino, Curt D Wolfgang, Sarika Jain, Wenli Tao. Population pharmacokinetic and exposure-response modeling of the oral selective estrogen receptor degrader, rintodestrant (G1T48), in patients with ER+/HER2- advanced breast cancer [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS17-08.

450. Evaluation of Linezolid Pharmacokinetics in Obese Patients with Severe Skin and Soft-Tissue Infections

Background

Linezolid is an oxazolidinone antibiotic with broad activity against Gram-positive bacteria and serves as an option for treating severe skin and soft-tissue infections (SSTIs). Adult FDA-labeled dosing is fixed at 600 mg IV/PO twice daily. Although conflicting, current literature is suggestive that critically ill, obese patients require increased doses. Based on this literature, our institutional guidelines recommend linezolid 600 mg every 8 hours for patients ≥150 kg. This study aimed to determine whether obese patients receiving linezolid for severe SSTI attain pharmacokinetic/pharmacodynamic (PK/PD) targets.

Methods

Adult patients with a body mass index (BMI) ≥30 who were hospitalized and receiving IV linezolid were eligible for consent in this prospective cohort study. A severe SSTI was defined by one of the following: necrotizing fasciitis, myonecrosis, or SSTI with sepsis based on qSOFA score or SIRs criteria. Four blood samples were collected at steady state, after at least 3 linezolid doses, at 2, 4, and 6 hours after the dose and as a trough before the next dose. Linezolid serum concentrations were determined by HPLC. Non-compartmental methods in Phoenix-WinNonlin (Version 6.4) were used to estimate individual PK parameters. The PK parameters were used to determine the concentration-time profile assuming one-compartment kinetics. Target attainment was defined as achieving a 24-hour area under the curve (AUC_0–24)/minimum inhibitory concentration (MIC) ≥100 or time above the MIC ≥ 85%.

Results

Eleven patients were included in the study. The median BMI was 45.7 (34.6–72.7) and median total body weight was 141.3 kg (99.9–188). Necrotizing fasciitis was the most common SSTI type at 45.5%. Four patients received linezolid 600 mg every 8 hours, 3 patients of which were ≥150 kg. Two patients received renal replacement therapy at the time levels were drawn. Based on non-compartmental analysis, the mean AUC_0–24 was 208.1 hr*mg/L (± 85.3). All but one patient, who grew E. faecalis with a MIC of 2, met PK/PD targets based on AUC/MIC ≥100. All patients achieved concentrations above MIC for 100% of the dosing interval.

Conclusion

All patients met defined PK/PD targets with linezolid doses received. This study validates current institutional dosing guidelines for patients with severe SSTIs.

Disclosures

All authors: No reported disclosures.