Which route bypasses the gastrointestinal tract entirely and provides 100% bioavailability?
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Clinical Pharmacology · Introduction to Pharmacology
Routes of Administration
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The route of administration is the path a drug takes to enter the body — oral, injected, applied to skin, inhaled, and more. Route determines how fast a drug acts, how much of it actually reaches the bloodstream (bioavailability), and whether it must survive the liver's "first-pass" metabolism before working. Nurses choose or verify routes based on how quickly a drug must work, the patient's condition, and drug properties like stability in stomach acid. Getting the route wrong can mean a drug that never works, works too slowly, or overdoses the patient.
The college version
Route of administration refers to the pathway by which a medication is introduced into the body to produce its effect. Routes are grouped into three broad categories: enteral (via the gastrointestinal tract), parenteral (bypassing the GI tract, typically by injection), and other routes such as topical, transdermal, and inhalation.
Enteral Routes
Enteral routes use the digestive tract. Oral (PO) administration is the most common: convenient, inexpensive, and generally safe, but subject to variable absorption, gastric pH, food interactions, and the first-pass effect — hepatic metabolism that can markedly reduce the amount of active drug reaching systemic circulation after absorption from the gut and transport via the portal vein. Sublingual (under the tongue) and buccal (between cheek and gum) routes place the drug against highly vascular mucosa, allowing rapid absorption directly into systemic circulation while bypassing first-pass metabolism — nitroglycerin for chest pain is a classic example. Rectal administration is useful when a patient cannot swallow or is vomiting; it partially bypasses first-pass metabolism, though absorption can be irregular.
Parenteral Routes
Parenteral routes bypass the digestive system entirely, usually via needle. Intravenous (IV) delivery places drug directly into the bloodstream, producing the fastest onset and 100% bioavailability — essential in emergencies but also carrying the highest risk, since there is no way to "take it back" once infused. Intramuscular (IM) injections deposit drug into muscle tissue, which is well-vascularized, allowing moderately fast absorption; this route is used for vaccines and depot (extended-release) formulations. Subcutaneous (subcut) injections go into the fatty layer beneath the skin, where slower, steadier absorption suits drugs like insulin and heparin. Intradermal injections deposit a small volume just beneath the epidermis, where absorption is intentionally slow; this route is used for tuberculin skin testing and allergy testing because it allows a localized, observable reaction.
Topical, Transdermal, and Inhaled Routes
Topical application delivers a drug to a local body surface (skin, eye, ear) for a local effect, such as a corticosteroid cream. Transdermal systems (patches) are designed for sustained systemic absorption through the skin over hours to days, providing steady blood levels — fentanyl and nicotine patches are examples. Inhalation delivers drug directly to the lungs' enormous absorptive surface, producing rapid onset for local respiratory effects (bronchodilators) or fast systemic effects, since pulmonary capillaries feed directly into systemic circulation without first-pass metabolism.
Why Route Matters
Route choice is a clinical decision balancing speed, reliability, and safety. Onset generally follows the order IV > inhalation > IM/subcut > oral/rectal, though this varies by drug formulation. Bioavailability — the fraction of an administered dose that reaches systemic circulation unchanged — is 100% by definition for IV drugs but can be much lower and more variable for oral drugs due to incomplete absorption and first-pass metabolism. Nurses must know each route's expected onset, proper technique, appropriate sites, and complications (infiltration, abscess, tissue damage) to administer safely and to recognize when a prescribed route is inappropriate for a patient's condition, such as ordering an oral medication for a patient who is NPO or unconscious.
Eli explains
The same idea, in plain words
Explain it like I’m 10
Imagine you want to send a message to a friend across town. You could mail a letter (slow, has to go through the post office first — like an oral pill going through your gut and liver), text them directly (instant — like an IV medicine going straight into your blood), or slide a note under their door (medium speed, local — like a shot into muscle). Each way of sending the message gets there differently, and some ways are faster or more reliable than others. A drug's "route" is just which way it travels to reach the place in your body where it needs to work. Doctors and nurses pick the fastest, safest way to send the message depending on how urgently the body needs it.
Check yourself
2 review questions from the chapter. Try each one, then open the answer.
A patient is vomiting repeatedly and cannot keep anything down, but needs pain medication soon. Which non-oral route might a nurse consider, and why?
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A rectal, IV, or IM route could be considered.
Since the patient can't swallow or keep oral medicine down, the nurse needs a route that doesn't rely on the stomach — rectal suppositories, an IV line, or an intramuscular injection can all deliver the drug without needing the patient to swallow or absorb it through the gut.
An intradermal injection is used for a tuberculin skin test rather than a subcutaneous or IM injection. What property of the intradermal route makes it suitable for this purpose?
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Intradermal injections are absorbed very slowly because the drug stays trapped in the dense dermis with little blood flow to carry it away.
This slow, localized absorption keeps the small test dose sitting right at the injection site long enough for a visible reaction (like swelling or redness) to develop and be measured, which is exactly what a skin test needs.
Quick check
3 questions here. Answers stay hidden until you check.
Why do sublingual and buccal medications avoid the first-pass effect?
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Which route is best suited for a drug that needs slow, steady absorption over several days?
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