Pharmacokinetics is currently defined as the study of the time course of drug absorption, distribution, metabolism, and excretion. Primary goals of pharmacokinetics include enhancing efficacy and decreasing toxicity of drug therapy. These parameters have enabled clinicians to apply pharmacokinetic principles to actual patient situations. Pharmacodynamics refers to the relationship between drug concentration at the site of action and the resulting effect, including the time course and intensity of therapeutic and adverse effects. Pharmacodynamics places a particular emphasis on dose–response relationships, it provides an important parameter for the clinical application of drugs.