Routes of Drug Administration

Drugs are administered by different routes of administration to treat local or systemic conditions. Systemically acting drugs must be absorbed into the systemic circulation, where they are distributed to all parts of the body, including their site of action. In contrast, locally acting drugs usually produce their effects at or in locations adjacent to their site of administration. Whether used for their local or systemic effects, drugs are exposed to various physiological conditions and must overcome biological barriers before they can reach their site of effect. The physiological characteristics and biological barriers vary based on the different routes of drug administration. The choice of the route of drug administration is usually based on drug physicochemical properties, drug product formulation, physiological conditions at the different sites of drug administration, and nature of the condition under treatment. The drug product must be designed to suit the biological environment at each route of drug administration and to optimize the drug availability at the intended site of action.