Drug administration involves delivering drugs to the body through various routes, such as enteral, parenteral, and topical.

Enteral administration refers to drugs absorbed through the gastrointestinal tract. They can be swallowed (perorally), placed under the tongue (sublingually), or on the inner lining of the cheeks (buccally). Perorally administered drugs take time to be absorbed and have a slower onset of action. The rectal route is another form of enteral administration, which allows for faster absorption through the rectal mucosa.

Parenteral administration involves delivering drugs directly into the bloodstream. This can be done through intravenous (IV), intramuscular (IM), or subcutaneous (under the skin) injections. IV drugs have high bioavailability and provide a rapid onset of action, making them suitable for emergencies.

Topical administration involves using ointments or sprays to apply drugs directly to the skin or mucous membranes.

Absorption is the process of a drug moving from the administration site into the bloodstream. It is crucial for all routes of administration except for intravenous injection, where absorption is immediate. In most cases, the drug must enter the bloodstream before reaching its site of action.

Other routes of administration include application to epithelial surfaces, inhalation, transnasal, vaginal, intrathecal, intraosseous,and intravitreal injections.

The choice of administration route is primarily determined by the drug's properties, such as solubility and ionization, as well as therapeutic objectives and target location. Enteral administration is commonly used for its safety, convenience, and cost-effectiveness. Parenteral routes are preferred for drugs with poor GI absorption, unstable in the GI tract, or requiring rapid action. Topical administration is suitable for localized treatment.