Pharmacodynamics refers to how a drug affects the body, including its mechanism of action, interactions with receptors, and physiological effects. Pharmacotherapeutics, on the other hand, involves the practical application of drugs to treat medical conditions. The relationship between the two lies in understanding how the pharmacodynamics of a drug influences its therapeutic use and potential benefits for patients. In other words, pharmacodynamics provides the scientific basis for the selection and use of drugs in pharmacotherapeutics.