Designing phase I oncology dose escalation using dose-exposure-toxicity models as a complementary approach to model-based dose-toxicity models.

One of the objectives of oncology phase I dose-escalation studies has been to determine the maximum tolerated dose (MTD). Although MTD is no longer set as the dose for further development in contemporary oncology drug development, MTD determination is still important for informing the therapeutic index. Bayesian adaptive model-based designs are becoming mainstream in oncology first-in-human trials. Herein, we illustrate via simulations the use of systemic exposure in Bayesian adaptive dose-toxicity models to estimate MTD. We extend traditional dose-toxicity models to incorporate pharmacokinetic exposure, which provides information on exposure-toxicity relationships. We pursue dose escalation until the maximum tolerated exposure (corresponding to the MTD) is reached. By leveraging pharmacokinetics, dose escalation considers exposure and interindividual variability on a continuous rather than discrete domain, offering additional information for dose-escalation decisions. To demonstrate this, we generated 1000 simulations (starting dose of 1/25th the reference dose and six dose levels) for several different scenarios. Both rule-based and model-based designs were compared using metrics of potential safety, accuracy, and reliability. The mean results over simulations and different toxicity scenarios showed that model-based designs were better than rule-based methods and that exposure-toxicity model-based methods have the potential to valuably complement dose-toxicity model-based methods. Exposure-toxicity model-based methods had decreased underdose risk accompanied by a relatively smaller increase in overdose risk, resulting in improved net reliability. MTD estimation accuracy was compromised when exposure variability was large, emphasizing the importance of appropriate control of pharmacokinetic variability in phase I dose-escalation studies.

Population Pharmacokinetic Analyses and Model Validation of Tolvaptan in Subjects With Autosomal Dominant Polycystic Kidney Disease.

Tolvaptan is the first approved drug treatment to slow kidney function decline in adults at risk of rapidly progressing autosomal dominant polycystic kidney disease (ADPKD). The objective is to develop (1091 subjects, 7335 observations) and validate (678 subjects, 3012 observations) a population pharmacokinetic model to describe tolvaptan pharmacokinetics in ADPKD subjects. The final model was evaluated with a bootstrapping method. The final model was internally and externally evaluated using visual predictive checks (VPC). Pharmacokinetics was best described by a 1-compartmental model with 0-order absorption, nonlinear relative bioavailability (F1), and first-order elimination. Accounting for changes in F1 significantly improved the model: as the dose increased from 15 mg to 120 mg, F1 decreased by 36%. Population estimates for clearance/F (CL/F), volume of distribution/F (Vd/F), duration of absorption (D1), the highest dose at which F1 is lowest, and the amount of dose at which F1 is 50% were 12.6 L·h-1 , 110 L, 0.58 hour, 182 mg, and 166 mg, respectively. The interindividual variability was 64% in CL/F, 70% in Vd/F, and 238% in D1. Residual variability was described by a combined-error model. The VPC (500 data sets simulated) showed that 76% to 92% of the observed data fell within the 90% prediction intervals. The model stability assessed by a 1000-run bootstrap analysis showed that the mean parameter estimates of data were within 10% of those obtained with the final model. The developed model is robust and stable. Internal and external validation confirmed the model ability to describe the data optimally.

AUC-Guided Vancomycin Dosing in Adolescent Patients With Suspected Sepsis.

Vancomycin is a first-line treatment for ß-lactam-resistant Gram-positive bacterial infections. Understanding the pharmacokinetic (PK) and pharmacodynamic (PD) characteristics of vancomycin in an adolescent population is of clinical importance in this often overlooked pediatric population. This retrospective study investigated vancomycin PK-PD in an adolescent cohort (12 to 18 years of age) of 463 patients (57% male, 81% white) admitted to the Intermountain Healthcare System between January 2006 and December 2013. Population PK modeling was performed in NONMEM 7.3. Vancomycin PK was well described with a 1-compartment model that identified both body weight (WT) and creatinine clearance (CRCL) as covariates significantly impacting vancomycin disposition. The model was then utilized to determine dosing strategies that achieved the targeted area under the 24-hour time curve vs minimum inhibitory concentration (AUC0-24 /MIC) ratio of ≥400. Additionally, these data were correlated with minimum steady-state concentrations (Css,min ) to find an acceptable target trough concentration range in adolescents. This analysis demonstrated that Css,min ranging from 10 to 12.5 mg/L were highly predictive of achieving an AUC0-24 /MIC ≥400 when the MIC was ≤1 mg/L. These results suggest that the target trough concentration for adolescents may be lower than that for adults.

Perceived stress and quality of life among doctor of pharmacy students.

OBJECTIVES: To examine stress and health-related quality of life (HRQOL) among third-year doctor of pharmacy (PharmD) students. METHODS: Stress and HRQOL were determined using Perceived Stress and SF-12 HRQOL survey instruments. A questionnaire was administered to determine factors students believed produced and eliminated stress. RESULTS: Eighty percent of third-year students participated (n=109) in this pilot study. Mental HRQOL scores were significantly below US mean score for individuals aged 20-34 years (p<0.0001). As stress increased, mental HRQOL decreased and a significant negative correlation was found between the 2 measures (p<0.001). Family and relationships, examinations and scheduling, outside-of-class assignments, and finances were the most common stress triggers reported by students, while exercising, spending time with friends/family, sleeping, watching TV, and drinking alcohol were the most commonly reported stress-alleviating activities. CONCLUSION: Third-year PharmD students reported relatively high levels of stress and low mental HRQOL. Students employed mostly positive, but some negative, lifestyle choices to alleviate stress. Further investigation into the effectiveness of students' coping strategies is needed.