Final answer:
The oral route is preferred for medication administration due to its convenience, with absorption occurring through the gastrointestinal tract. Poorly absorbed drugs may be given by parenteral routes. Drug absorption can be transcellular, paracellular, or active, depending on the drug's characteristics.
Step-by-step explanation:
The oral route is a common method for medication administration due to its convenience for patient use at home. Medications intended for systemic effects must be absorbed from the gastrointestinal (GI) tract into the bloodstream. Medicines such as niclosamide for tapeworms or colistin for bowel decontamination may be intentionally designed for poor absorption to treat the intestinal tract directly. Topical preparations like bacitracin or antifungal agents are used for superficial skin infections due to their poor systemic absorption.
When oral administration is not feasible or the medication does not absorb well in the GI tract, healthcare providers may resort to parenteral routes including intravenous or intramuscular injections. The dosage and route of administration are critical and vary depending on factors such as the individual's age, body mass, and liver or kidney function.
Absorption for water-soluble nutrients typically requires active transport fueled by ATP, while lipid-soluble nutrients can diffuse through cell membranes and be transported via lymphatic vessels. The efficacy of a drug depends on its absorption characteristics, which may be passive, through transcellular diffusion or paracellular pathways, or active, involving transport proteins.
It's noteworthy that chemical digestion and some absorption can occur in the mouth and stomach, as seen with substances like alcohol and aspirin.