Introduction to pharmacodynamics

In this second article in the series of ‘bite-sized’ pharmacology we will look at the principles of pharmacodynamics. It is important that prescribers are aware of the actions that drugs have on the body following administration. Prescribers should know the site of action (where the drug works), the mode of action (how the drug works) and the time to onset and duration of action (when the drug starts to work and how long for). This helps prescribers decide on drug choice, drug dose and the dose schedule as well as the length of time the drug needs to be prescribed for. This knowledge can also assist the prescriber in prediction and prevention (or minimising) of adverse drug reactions and to help educate their patients on possible side effects. In this article, we will look at sites of action: receptors, ion channels, enzymes, and transport systems. We will also introduce the concepts of agonism and antagonism and their relationship to mode of action