Aging-Related CYP3A Functional Changes in Chinese Older Patients: New Findings from Model-Based Assessment of Amlodipine.

Aging-related alterations in hepatic enzyme activity, particularly of the CYP3A, significantly impact drug efficacy and safety in older adults, making it essential to understand how aging affects CYP function for optimal drug therapy. The exogenous probe substrate method, a minimally invasive approach to assess liver metabolic enzyme activity in vivo, is effective in studying these changes. Amlodipine being extensively metabolized (> 90%) in the liver, primarily via cytochrome P450 enzyme CYP3A was selected as a probe to investigate and quantify the factors affecting the aging-related changes of CYP3A in the Chinese older population. Amlodipine concentration data were collected from an ongoing noninterventional clinical study conducted at Peking University Third Hospital. A physiologically-based pharmacokinetic modeling approach, grounded in population pharmacokinetic (PPK) analysis, was employed to physiologically quantify the aging-related changes in CYP3A function. A total of 132 amlodipine concentrations from 69 patients were obtained from the clinical study. PPK analysis shows that frailty phenotype but not age is a significant influence and frail patients have 37% greater plasma amlodipine exposure than nonfrail patients. This difference in CYP3A function may be attributed to a 63.2% lower CYP3A relative abundance in the frail patients, compared with that in the nonfrail patients. In the context of dose selection for older adults, focusing on frailty rather than chronological age should be recognized as a more relevant approach, because frailty might more accurately reflect the individual's biological age. Our study suggested a need to shift the research focus from chronological age to biological age.

Development of a physiologically based pharmacokinetic (PBPK) population model for Chinese elderly subjects.

AIMS: This study aims to develop and verify a physiologically based pharmacokinetic (PBPK) population model for the Chinese geriatric population in Simcyp. METHODS: Firstly, physiological information for the Chinese geriatric population was collected and later employed to develop the Chinese geriatric population model by recalibration of corresponding physiological parameters in the Chinese adult population model available in Simcyp (i.e., Chinese healthy volunteer model). Secondly, drug-dependent parameters were collected for six drugs with different elimination pathways (i.e., metabolized by CYP1A2, CYP3A4 or renal excretion). The drug models were then developed and verified by clinical data from Chinese adults, Caucasian adults and Caucasian elderly subjects to ensure that drug-dependent parameters are correctly inputted. Finally, the tested drug models in combination with the newly developed Chinese geriatric population model were applied to simulate drug concentration in Chinese elderly subjects. The predicted results were then compared with the observations to evaluate model prediction performance. RESULTS: Ninety-eight per cent of predicted AUC, 95% of predicted Cmax , and 100% of predicted CL values were within two-fold of the observed values, indicating all drug models were properly developed. The drug models, combined with the newly developed population model, were then used to predict pharmacokinetics in Chinese elderly subjects aged 60-93. The predicted AUC, Cmax , and CL values were all within two-fold of the observed values. CONCLUSION: The population model for the Chinese elderly subjects appears to adequately predict the concentration of the drug that was metabolized by CYP1A2, CYP3A4 or eliminated by renal clearance.

Dose selection of chloroquine phosphate for treatment of COVID-19 based on a physiologically based pharmacokinetic model

Chloroquine (CQ) phosphate has been suggested to be clinically effective in the treatment of coronavirus disease 2019 (COVID-19). To develop a physiologically-based pharmacokinetic (PBPK) model for predicting tissue distribution of CQ and apply it to optimize dosage regimens, a PBPK model, with parameterization of drug distribution extrapolated from animal data, was developed to predict human tissue distribution of CQ. The physiological characteristics of time-dependent accumulation was mimicked through an active transport mechanism. Several dosing regimens were proposed based on PBPK simulation combined with known clinical exposure-response relationships. The model was also validated by clinical data from Chinese patients with COVID-19. The novel PBPK model allows in-depth description of the pharmacokinetics of CQ in several key organs (lung, heart, liver, and kidney), and was applied to design dosing strategies in patients with acute COVID-19 (Day 1: 750 mg BID, Days 2-5: 500 mg BID, CQ phosphate), patients with moderate COVID-19 (Day 1: 750 mg and 500 mg, Days 2-3: 500 mg BID, Days 4-5: 250 mg BID, CQ phosphate), and other vulnerable populations (.., renal and hepatic impairment and elderly patients, Days 1-5: 250 mg BID, CQ phosphate). A PBPK model of CQ was successfully developed to optimize dosage regimens for patients with COVID-19.