Bio pharmaceutics is a major branch of pharmaceutical sciences which relates between the physiochemical properties of drugs in dosage form and pharmacology, toxicology, or clinical responses observed after administration. Clinical pharmacokinetics is the discipline that describes the absorption, distribution, metabolism, elimination of drugs in the patients requiring drug therapy. Clearance is the important pharmacokinetic parameter because it determines the steady state concentration for a given dose rate. The volume of distribution is a proportional constant that relates the amount of drug in the body to serum concentration. Pharmacodynamics is the quantitative study of the relation between drug exposure and pharmacologic or toxicologic responses. Pharmacodynamics interactions are where the actions of one drug are changed in presence of other Toxicokinetics is an crucial step in clinical toxicology. The methodology is based on pharmacokinetic parameters by the exact knowledge of toxicokinetics. It is possible to determine for each toxicon the relevant parameters which will be of use in clinical practice. The dose–response relationship, describes the change in effect on an organism caused by differing levels of exposure to an after a certain exposure time.