Introducing Pharmacokinetic and Pharmacodynamic Concepts
All effective drugs have the potential for producing both benefits and risks associated with desired and undesired effects. The particular response to a drug by a patient is driven in one way or another by the concentration of that drug, and sometimes its metabolites, at the effect sites within the body. Accordingly, it is useful to partition the relationship between drug administration and response into two phases, a pharmacokinetic phase, which relates drug administration to concentrations within the body produced over time, and a pharmacodynamic phase, which relates response (desired and undesired) produced to concentration. In so doing, we can better understand why patients vary in their response to drugs, which includes genetics, age, disease, and the presence of other drugs.