Pharmacodynamics is the study of what a drug does to the body. In most cases, it is a study of a drug’s interaction with an intended receptor, the target in the body that binds the drug to a person’s physiological systems. There are several areas of interest in this field of research, including drug targeting to a specific site in the body, drug efficiency across age groups and unintended side effects of a drug. Pharmacodynamics' counterpart is pharmacokinetics, the study of what a body does to a drug.
In order for most drugs to work, they must be targeted to a receptor in the body or to a microorganism within the body, such as a bacterial infection. A receptor is a specific type of protein that sticks out from a cell’s body. Drugs are given a different protein, called a ligand, which can connect with the receptor. The two proteins snap together like pieces of a puzzle, and the binding acts like a trigger, setting a course of chemical reactions into motion, such as a drug beginning the process of combating a disease. Knowing which sort of ligand to attach to a drug is an important part of pharmacodynamics.
One of the most significant areas of study in pharmacodynamics is ensuring that drugs are efficient across a wide range of ages and stages of disease. As people age, the receptors in their bodies change. Many drugs need receptors to which to bind, so drugs might need to be created with multiple ligands that can bind to multiple receptors to cover an age range. The same is true for diseases that are long-term and degenerative, such as Alzheimer’s disease, which goes through many stages and causes the person’s brain cells to deteriorate as the disease progresses. Therefore, a drug that targets late-stage Alzheimer’s would need a different structure than one that targets an early stage of the disease.
Another facet of pharmacodynamics is learning and understanding all of the effects that a drug might have in the body once it has bound to its intended receptor. Drugs are, of course, supposed to change what is happening in the body. They can alter how a virus is replicating, inhibit tumor growth or bolster the immune system. In the early stages of drug development, however, pharmacodynamics is used to study all of the unintended consequences of drug binding. The side effects might include causing damage to the body’s cells, inducing cell mutation that might lead to cancerous growths or, in a worse-case-scenario, actually increasing a disease’s potency.