Tutorial: Statistical analysis and reporting of clinical pharmacokinetic studies.

Pharmacokinetics is the cornerstone of understanding drug absorption, distribution, metabolism, and elimination. It is also the key to describing variability in drug response caused by drug-drug interactions (DDIs), pharmacogenetics, impaired kidney and liver function, etc. This tutorial aims to provide a guideline and step-by-step tutorial on essential considerations when designing clinical pharmacokinetic studies and reporting results. This includes a comprehensive guide on how to conduct the statistical analysis and a complete code for the statistical software R. As an example, we created a mock dataset simulating a clinical pharmacokinetic DDI study with 12 subjects who were administered 2 mg oral midazolam with and without an inducer of cytochrome P450 3A. We provide a step-by-step guide to the statistical analysis of this clinical pharmacokinetic study, including sample size/power calculation, descriptive statistics, noncompartmental analyses, and hypothesis testing. The different analyses and parameters are described in detail, and we provide a complete R code ready to use in supplementary files. Finally, we discuss important considerations when designing and reporting clinical pharmacokinetic studies. The scope of this tutorial is not limited to DDI studies, and with minor adjustments, it applies to all types of clinical pharmacokinetic studies. This work was done by early career researchers for early career researchers. We hope this tutorial may help early career researchers when getting started on their own pharmacokinetic studies. We encourage you to use this as an inspiration and starting point and continuously evolve your statistical skills.

Therapeutic Drug Monitoring of Venlafaxine in an Everyday Clinical Setting: Analysis of Age, Sex and Dose Concentration Relationships.

Venlafaxine is a commonly used antidepressant agent. We aimed to provide detailed information on the associations between venlafaxine dose and concentrations of venlafaxine, by patient age and sex. From a therapeutic drug monitoring (TDM) database located at Odense University Hospital, Denmark, we identified all adults for whom the treating physician had requested clinical advice on the TDM result for venlafaxine between 2002 and 2012. We identified 1077 TDM samples of venlafaxine from 334 males and 743 females (median age 45 years), and the median daily dose was 225 mg. Median plasma concentration of venlafaxine and o-desmethylvenlafaxine (ODV) was 306 nmol/L and 861 nmol/L, respectively. The median dose-corrected serum level for venlafaxine was 1.49 nmol/L/mg., while the dose-corrected serum level of men and women were 1.21 nmol/L/mg and 1.60 nmol/L/mg, respectively. The dose-corrected sum of venlafaxine and ODV was 8.91 nmol/L/mg (IQR 6.56-12.26) versus 5.52 nmol/L/mg (IQR 4.16-7.52) for patients above 64 years and below the age of 65 years, respectively. Dose-corrected plasma concentrations of venlafaxine and ODV are increased to a clinically significant degree in patients above the age of 64, and initiation of venlafaxine therapy in the elderly should be made cautiously and supported by drug measurements.