Identification of vancomycin exposure target in neonates: how much is enough?

OBJECTIVES: Vancomycin is commonly used in neonates with the same pharmacokinetics/pharmacodynamics (PK/PD) target as adults. However, no evidence supports this practice, and the association between trough concentrations and treatment outcomes has been widely questioned. This study aimed to identify the optimal PK/PD predictor and assess the correlation between AUC/MIC, trough concentration and the vancomycin efficacy in neonates. METHODS: This study retrospectively collected neonates who used vancomycin and constructed a population pharmacokinetic (PPK) model to estimate the AUC. Logistic analyses were used to identify the variables related to efficacy. Classification and regression tree analysis was used to explore thresholds. The correlation between trough concentration and AUC/MIC on the first day was analysed using a linear regression model. RESULTS: PPK modelling involved 131 neonates. Postmenstrual age and current weight were included in the covariate analysis. Forty-eight patients were included in the efficacy analysis, 13 of whom were infected with MRSA. The best-performance PK/PD target for efficacy was AUC0-24  h/MIC ≥ 331. The trough concentration was correlated with AUC0-24  h/MIC (r2 = 0.32), but individual differences existed. AUC0-24  h/MIC ranged up to 2.5-fold for a given trough concentration. CONCLUSIONS: AUC0-24  h/MIC ≥ 331 was the optimal target of vancomycin efficacy in neonates. The trough concentration was not a reliable predictor of efficacy and AUC0-24  h/MIC. AUC-guided dosage adjustments are more valuable in clinical applications.

Population Pharmacokinetics of Tenofovir Alafenamide Fumarate and Its Metabolite Tenofovir in Healthy Chinese Volunteers.

Tenofovir alafenamide fumarate (TAF) is a first-line drug for treating hepatitis B virus infection. This study aimed to establish the prodrug-metabolite population pharmacokinetic (PK) model for TAF and its metabolite tenofovir (TFV) in healthy Chinese volunteers and evaluate the factors affecting the PK. Using 1043 TAF and 1198 TFV plasma sample concentrations collected from 67 healthy volunteers, a population PK model was developed using the nonlinear mixed-effects model. The 1-compartment model containing 4 transit compartments and the 2-compartment model accurately described the PK of TAF and TFV, respectively. Covariates such as meal state and sex were found to be statistically significant and potentially clinically relevant. Both internal and external validations demonstrated good stability and predictive performance of the connected model. This study elucidated the PK process by which TAF was absorbed, converted, and finally metabolized and eliminated as TFV, and explored the sources of interindividual variability between TAF and TFV.

Effects of CYP2D6 *10 and *41 Variants in Healthy Chinese Men on the Pharmacokinetics of Dapoxetine.

Dapoxetine is a selective serotonin reuptake inhibitor (SSRI) used to treat premature ejaculation (PE), and is mainly metabolized by CYP2D6, CYP3A4, and flavin-containing monooxygenase 1. The purpose of the study was to evaluate the effect of CYP2D6 polymorphism on the pharmacokinetics of dapoxetine in healthy Chinese men. Thirty-nine subjects who received a single oral dose of 30 mg dapoxetine hydrochloride were classified based on their CYP2D6 genotype: *1/*1 (n = 9), *1/*41 (n = 1), *1/*10 (n = 12), *10/*41 (n = 3), or *10/*10 (n = 14). The difference in pharmacokinetic parameters between different genotype groups was analyzed and then scored according to the activity score system. Compared with the wild-type subjects of CYP2D6 *1/*1, the peak plasma concentration (Cmax ) and the area under the plasma drug concentration-time curve (AUCinf ) of dapoxetine in the *10/*10 and *10/*41 groups were notably increased (P ≤ .05). Significant differences in Cmax , AUC, volume of distribution/bioavailability (V/F) and clearance/bioavailability (CL/F) were observed among dapoxetine activity score groups (P ≤ .05). The AUCinf was increased significantly (154% and 89.73%, P ≤ .05) and the Cmax was increased significantly (73.45% and 42.67%, P ≤ .05) in CYP2D6 *10/*41 subjects, compared with CYP2D6 *1/*1 and *1/*10 subjects. The results obtained indicated that CYP2D6 *10 and *41 polymorphisms have significant effects on the pharmacokinetic properties of dapoxetine.

Population Pharmacokinetic Analysis of Valsartan in Healthy Chinese Subjects.

The study was conducted to establish a population pharmacokinetic (PPK) model of valsartan in Chinese healthy subjects and investigate potential covariate impacts on the pharmacokinetics (PK) parameters. Data from a bioequivalence study with 78 Chinese healthy subjects were retrospectively analyzed to develop a PPK model of valsartan. Phoenix NLME 8.1 was used to build a PPK model and quantify the effects of covariates, such as demographic data and biochemical, on the PK parameters of valsartan. For the healthy Chinese population, valsartan conformed to the two-compartment model with an absorption lag time. In the final PPK model, food affected the absorption rate constant, while aspartate aminotransferase, alanine aminotransferase, and creatinine affected the clearance of the central compartment. The final PPK model was verified to be reproducible, and it can be used to evaluate the PK parameters. This is the first research describing the PPK profile of valsartan in healthy Chinese subjects, and it is expected to provide relevant PK parameters for further study of valsartan.