Effective and safe drug therapy is predicated on pharmacodynamic and pharmacokinetic variable. Pharmacodynamics relates to drugs-receptor interactions and provides quantitative information that is the basis for determining efficacy, potency, and toxicity of drugs. Pharmacokinetics underlies the faith of drugs within the body, i.e., provides the basis for understanding the mechanisms responsible for a drug’s ability to reach its receptor and factors essential to maintain therapeutic concentration for optimum efficacy and safety.