**4. Routes of drug administration and systemic availability**

This depends on the actual biochemical characteristics of the drug and the interaction of drug molecules with body fluids and tissues. The main routes of drug administration are the topical application, parenteral, and enteral routes.

The route of drug application determines how quickly the drug reaches its site of action. The choice of the route of administration of a drug, therefore, depends on the therapeutic objectives of the treatment. For instance, intravenous injection or inhalation may be selected to produce intense, but rather short-lived effects, whereas oral dosing may be better and more convenient for long lasting effects and even intensity. The various types of drug administration include;
