Pharmacodynamics (sometimes described as what a drug does to the body) is the study of the biochemical, physiologic, and molecular effects of drugs on the body and involves receptor binding (including receptor sensitivity), postreceptor effects, and chemical interactions. Pharmacodynamics, with pharmacokinetics (what the body does to a drug, or the fate of a drug within the body), helps explain the relationship between the dose and response, ie, the drug's effects. The pharmacologic response depends on the drug binding to its target. The concentration of the drug at the receptor site influences the drug’s effect.
A drug’s pharmacodynamics can be affected by physiologic changes due to
Disorders that affect pharmacodynamic responses include genetic mutations, thyrotoxicosis, malnutrition, myasthenia gravis, Parkinson disease, and some forms of insulin-resistant diabetes mellitus. These disorders can change receptor binding, alter the level of binding proteins, or decrease receptor sensitivity.
Aging tends to affect pharmacodynamic responses through alterations in receptor binding or in postreceptor response sensitivity (see table Effect of Aging on Drug Response).
Pharmacodynamic drug–drug interactions result in competition for receptor binding sites or alter postreceptor response.