is one of the most important branches of Pharmacology which decides whether the drugs would reach the destined organs. It basically deals with the study of the fate of substances administered inside a living being. The substances can be any chemical like such as: , , , etc. It focusses on the chemical and to discover the fate of a chemical from the moment that it is introduced in our body up to the point at which it is completely . Pharmacokinetics deals with how an organism affects a drug, whereas (PD) deals with how the drug affects the organism. Both of them altogether influences , benefit, and , as seen in PK/PD models.