**3. Role of pharmacodynamics IN DRUG'S effect and response**

In basic, PD can be denoted as the determination of the effect of pharmacology and toxicology of the drug that appears as a result of the interaction occurred between the drug and receptor [11]. An individual drug's response to the target could be knocked off by the activities such as activation, inhibition of the targets' disease mechanisms at the active site described quantitatively with the support of PD. Depending on the activity of target and its biochemical pathway, the PD effects can be classified as direct, indirect, immediate, and delayed effects. The direct effect takes place in biochemical interaction pathway and the indirect effect occurs far from the end of the biochemical pathway.

With the knowledge of the drug concentration at the active site of the receptor, we can quantify the intense of the drug's effect and the magnitude of the response that is differing for the drug with the same concentration due to the disease and/or preadministered drug. The response could be interrupted by many criteria such as the density of receptor on cell surface, signal transmission, and some regulatory factors.

The apparent effects such as physiological, cellular, molecular, biochemical and toxicological effects are the products of the drug-receptor interaction that is significant to make decision about dosage/concentration of the drug. Respective to the response of the drug action, the distribution and dosage of the drug increases simultaneously [8].

#### **3.1 Physiological effects**

Physiological factors like body type, quantitative amount of drug action, time course of drug action to the target, produces the effect that could interrupt the actual
