Route of administration

A route of administration is the path by which a drug or other substance enters the body. It affects how quickly and completely the substance is absorbed and where it acts.

Drug absorption: The movement of a drug from its administration site into the bloodstream or another part of the body. Different routes expose drugs to distinct barriers before they reach circulation.
Oral administration: The delivery of a substance through the mouth for absorption in the gastrointestinal tract. It is a common route, but digestion and first-pass metabolism can alter drug exposure.
Enteral administration: Drug delivery through the gastrointestinal tract, including oral, rectal, and feeding-tube routes. It contrasts with parenteral delivery, which bypasses the gastrointestinal tract.
Onset of action: The time between administering a drug and the beginning of its observable effect. Routes that deliver a drug rapidly to its site of action can shorten this interval.
Bioavailability: The fraction of an administered dose that reaches systemic circulation in an active form. Route determines how much of a dose becomes available beyond its entry site.
Intravenous therapy: The delivery of fluids or drugs directly into a vein. It bypasses absorption barriers and provides immediate access to systemic circulation.
Parenteral administration: Drug delivery by routes that bypass the gastrointestinal tract, commonly through injection or infusion. Its injections and infusions avoid gastrointestinal absorption and digestion.
Therapeutic index: A measure comparing a drug’s toxic dose with its effective dose. Route-dependent exposure can change how closely therapeutic and harmful doses approach.
First-pass effect: The metabolism of a substance in the gut wall or liver before it reaches systemic circulation. Oral drugs may lose a substantial fraction of their dose before reaching circulation.
Intramuscular injection: The injection of a substance into skeletal muscle. Muscle tissue can absorb drugs gradually and serve as a depot for some formulations.

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