The Certara Blog

Author: Nathan Teuscher

Dr. Nathan Teuscher is the Vice President of Pharmacometric Solutions at Certara. He is an expert in clinical pharmacology, pharmacometrics, pharmacokinetics and pharmacodynamics and was trained by David Smith at the University of Michigan. Dr. Teuscher has held leadership positions in biotechnology, pharmaceutical and contract research companies. In 2008 he established the Learn PKPD.com website to share his knowledge with the community. Prior to coming to Certara, he was the Founder and President of PK/PD Associates.

Recent Posts

Feedback from the Phoenix Community: Our Visits with the FDA

We recently completed a week-long set of meetings with the FDA, where we met with over 300 FDA reviewers from 7 of the 11 FDA centers that use Phoenix. Here are a few topics that took center-stage during our visits: Q: How can we create Phoenix workflow templates that are reusable across different studies with […]

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Every Ending has a New Beginning

I created the Learn PK/PD site in May 2010 in response to a communication issue that I was facing in my daily work in the world of clinical pharmacology and pharmacokinetics. In my first post, I stated the reason for creating my blog and the website: My blog is dedicated to providing clear, concise, accurate, and […]

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9 Frequently Misunderstood Concepts in PK/PD Modeling

In teaching pharmacometrics, I’ve noticed that scientists have difficulty with certain PK/PD modeling concepts. Maybe you’ve read about some of these terms in journal articles, but didn’t know what they meant? Or you’ve heard these terms bandied about by colleagues, but felt too shy to ask them what they meant? I’ll clarify some important concepts […]

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9 Things Your Boss Wishes You Knew About PK/PD Modeling

Over the course of my career, I have taught the theory and practical applications of PK/PD modeling to hundreds of scientists. In this blog post, I’ll share some of my most popular tips for solving common difficulties encountered by pharmacometricians. The tools of the trade While I have worked with a number of pharmacometrics tools, I […]

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Derivation for Logarithmic Trapezoidal AUC Calculation

Calculating area under the curve requires the use of two separate equations: one is follows the “linear trapezoidal rule” and the other follows the “logarithmic trapezoidal rule.” These equations are normally presented in textbooks without derivations so all you have to do is insert the concentrations and times and you can calculate the area under […]

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Calculating the Elimination Rate Constant

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 […]

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Adding a Placebo Component to Your PK/PD Model in Phoenix

PK/PD modeling is an exciting are of research in clinical pharmacology. Most often we try to model the effect of a drug by drawing relationships between the concentration and effect. This usually entails subsetting the data to exclude information from subject that received placebo during the trial. But statistical comparisons in clinical studies are most […]

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Bioanalytical Calibration Curves

At the request of a reader, I have decided to extend my series on bioanalysis to include another topic: calibration curves. The calibration curve is they keystone of bioanalysis. It is what links the instrument response to a specific concentration of drug. It is like the magic decoder ring that helps you decipher the hidden […]

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Bioanalytical Method Validation

In this final post regarding bioanalysis, I will review a few of the main ideas related to bioanalytical method validation. The purpose of a method validation is to demonstrate that a specific bioanalytical method can reliably determine the concentration of drug in a study sample with a high degree of confidence. Validation does not mean […]

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Radiometric Analysis

One of the oldest methods used for the quantitation of drug molecules is radiometric analysis. This generally involves quantitation of radiation from beta-emitting radioactive isotopes such as 14C, 3H or 32P. Radiometric analysis is one of the most precise, sensitive, and efficient detection methods; however, there are many technical and social challenges with using this […]

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Ligand Binding Assays

Our discussions of various bioanalytical methodologies over the past few weeks has focused on chromatography and small molecule analysis. Today we are going to discuss a collection of methods that is commonly used for large molecules, such as peptides, peptides and macro-molecules. These molecules are often called “biologics” because they are generally derived from endogenous […]

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Understanding LC/MS/MS

The most common bioanalytical method in use today is LC/MS/MS, or liquid chromatography (LC) tandem mass spectrometry (MS). This is a very versatile, robust, and sensitive methodology that is used for nearly all small molecules. In addition, this technology is amenable to automation and unattended analysis. The LC/MS/MS methodology is very similar to HPLC/UV, which […]

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What is HPLC/UV?

In my series about bioanalysis for the pharmacokineticist, I thought I would start with the bioanalysis methodology that was in use when I began my career in pharmaceutical development: HPLC/UV. The first part of this method (HPLC) is the separation technology. The second part (UV) is the detection technology. In the remainder of this post, […]

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Bioanalysis from a PK Perspective

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 […]

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What Can We Learn from Dose Normalization?

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 […]

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Creating Templates in Phoenix WinNonlin

One of the most useful features of the new Phoenix WinNonlin software is the ability to re-use objects for new projects. In particular, it takes quite a bit of time to adjust all of the settings for figures in Phoenix. You need to adjust the font on both axes, change the legend labels, choose the […]

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Extrapolating AUC to Infinity

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 […]

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Simplifying Deconvolution

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 me define […]

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Cassette Dosing: Advantages and Challenges

Cassette dosing is a technique primarily used in drug discovery efforts in non-clinical studies to collect pharmacokinetic data from multiple drug candidates in a single experiment. A typical cassette dosing pharmacokinetic study involves simultaneous administration of 5-10 compounds to a set of animals. Serial blood samples are obtained and LC/MS/MS techniques are used to measure […]

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What is GLP (Good Laboratory Practice)?

Good laboratory practice or GLP is a set of principles intended to assure the quality and integrity of non-clinical laboratory studies that are intended to support research or marketing permits for products regulated by government agencies. The term GLP is most commonly associated with the pharmaceutical industry and the required non-clinical animal testing that must […]

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