Tag: Pharmacokinetics

The elimination rate constant is the rate at which drug is cleared from the body assuming first-order elimination. Various abbreviations are used to represent the elimination rate constant including ke, kel, λ, and λz. The calculation of the elimination rate constant can be done using pharmacokinetic parameters or it can be done directly from a […]

The field of bioanalytical chemistry, or bioanalysis, is an important area of research that has a direct impact on the work of pharmacokineticists. Essentially, bioanalysis converts a blood sample (or any other matrix) into a drug concentration by the use of analytical equipment. Over the next few weeks, I would like to cover a variety […]

Dose normalization is a common calculation performed with pharmacokinetic parameters. The general process is to divide the PK parameters by the administered dose. This is performed for each individual or treatment group in a study, and then comparisons of dose-normalized parameters can be performed. But, why would we want to dose normalize PK parameters? What […]

Area under the curve or AUC is a pharmacokinetic statistic used to describe the total exposure to a drug. More specifically, it is the time-averaged concentration of drug circulating in the body fluid analyzed (normally plasma, blood or serum). Standard calculation of AUC involves using non-compartmental techniques to calculate the AUC from time 0 to […]

    Deconvolution is used to evaluate the absorption kinetics of a drug. Unfortunately the term can be confusing and explanations are generally even more confusing. While deconvolution is not a simple topic, I believe it can be understood so that more scientists can apply the principles to their work. Before I define deconvolution, let […]

Linear regression is a common tool that the pharmacokineticist uses to calculate elimination rate constants. Standard linear regression provides estimates for the slope, intercept, and r2, a statistic that helps define goodness of fit. Statistical texts define r2 as the coefficient of determination and it is calculated using the following equation: where SS = the sum of […]

In this post, I am reviewing the Phoenix Connect package from Certara. Over the past several years, Certara has made a significant effort to modernize the pharmacokinetic analysis software tools to aid in the drug development process. While many longtime users of the PCNonlin and WinNonlin software solutions are disappointed with the need to learn […]

When I first began learning about pharmacokinetics, I was often confused by the mean residence time (MRT) parameter. I wasn’t really sure what it meant, how to interpret the value, and why it would ever be important. After many years of working with pharmacokinetic analysis, I still do not use MRT very often, but I […]

The superposition principle has nothing to do with a super-hero; however, you might be perceived as a hero if you can explain the principle to others. The superposition principle is a mathematical concept that helps us analyze concentration-time data. While it may seem complicated, it is actually nothing more than addition! The superposition principle states […]

Drug absorption is the process by which a drug molecule moves from the site of administration to the systemic circulation. Following intravenous administration, there is no absorption process since the drug is directly introduced into the blood stream. However, for oral, intramuscular, subcutaneous, sublingual, buccal, transdermal, (and many other routes), there will be an absorption […]

You may come across a phrase like the following and wonder what it means: “… this drug exhibits nonlinear pharmacokinetics …”. An example of a drug that has nonlinear pharmacokinetics (PK) is erythropoietin or EPO. You may have heard about EPO in the context of sports because it is a performance enhancing drug (PED). EPO […]

The maximum observed concentration (Cmax) and the time of Cmax (tmax) are both obtained directly from the concentration-time data. In this post, I will review how to determine both of these parameters, and how to interpret information from the values. These two parameters are simple, but they pack some important information if you know how […]

One of the most common tasks when working with data in Phoenix WinNonlin is to change the column titles or units. In many software packages that consists of clicking on the data spreadsheet and re-typing the new information; however, with Phoenix, you have to take a few additional steps. Here’s some quick tips on how […]

Phoenix WinNonlin is Certara’s new implementation of the popular pharmacokinetic software that has been the mainstay of non-compartmental analysis for over 15 years. But, this newest version is the biggest change in the software since the original PC Nonlin was converted to the Windows-based “WinNonlin” (i.e. Windows Nonlin). In Phoenix WinNonlin, there are a powerful […]

Pharmacokinetic analysis normally focuses on systemic exposure to a drug; however, much can be learned from urinary pharmacokinetic parameters. Urinary PK parameters tell you about how much drug was absorbed (at a minimum), and how much drug is eliminated through the kidney. Often it provides easy access to metabolites that are also eliminated in the […]

A reader, Michael, asked me to discuss the concept of accumulation. This term is used frequently in both the nonclinical and clinical setting. Some people use the word with fear, while others explain it in complicated terms. Accumulation represents the relationship between the dosing interval and the rate of elimination for the drug. When the […]

The term bioavailability is used very frequently in pharmacokinetic discussions. Often it is misused and complicated by those who don’t understand its meaning. Bioavailability simply means the fraction of administered drug that reached the systemic circulation (blood). It can range from 0% (no drug) to 100% (all of the administered drug). Absolute vs Relative The […]

I apologize to all my readers for such a long lapse between posts. After a very busy summer and fall, I am back to posting regularly to my blog about PK/PD topics. When analyzing PK/PD data, one of the most important plots used to visualize the data is to plot time-matched PK/PD data on a […]