What is Pharmacodynamics?

Starting with definitions is always helpful… so after defining pharmacokinetics, a definition for pharmacodynamics is in order. The definition of pharmacodynamics (PD) is much less controversial than the definition for pharmacokinetics.

The word pharmacodynamics is from two Greek words (see wikipedia for more):

pharmakon: Drug
dynamikós : force or power

Thus, pharmacodynamics is the study of the effects of drugs.

Whether we are talking about pharmaceutical therapeutics or recreational drugs, people take drugs to achieve a desired pharmacological effect. And two key questions often asked prior to taking the drug are: “How long before I feel the effect?” and “How long will the effect last?” Both of these questions can be answered by using pharmacodynamic analyses.

Most drugs are developed based on the theory that the drug interacts with a biological structure (eg, receptor, enzyme, transporter, etc.), and that interaction leads to a specific effect on the body. The strength and length of this interaction determines how quickly the drug initiates the effect, and how long the effect lasts.


Penicillin is recognized as one of the first drugs to enter mass production, leading to a significant reduction of bacterial infections across the world. Penicillin is an antibiotic, which means it kills bacteria. The penicillin molecule binds to a bacterial enzyme (DD-transpeptidase) that creates “cross-links” in the bacterial cell wall, preventing the cross-linking action. Thus penicillin prevents bacteria from creating strong cell walls, in effect killing the bacteria. The interaction between penicillin and the DD-transpeptidase enzyme depends on the amount of penicillin present. When large amounts of penicillin are available, the enzyme is completely blocked. When small amounts of penicillin are available, the enzyme resumes normal function. Thus the bacterial-killing activity of penicillin changes as drug levels in the body change. This is considered the “pharmacodynamics” of penicillin. Using this information, physicians can properly prescribe the penicillin dosing frequency to ensure high drug levels over the course of treatment.

Today’s pharmacokineticists and PK/PD modelers are under more pressure than ever to quickly and accurately characterize the safety and efficacy profiles of investigational drugs. They need the right tools to perform non-compartmental analysis (NCA), build pharmacometric models, and generate reports that communicate their findings.

Phoenix 7.0’s new features and enhancements are the direct result of user feedback we received to make the world’s most advanced PK/PD software package even better.

Watch this webinar to learn how Phoenix 7.0 helps you handle bigger datasets, perform lightning-fast NCA, and make gorgeous plots.