Routes of Administration

Pharmacology Basics

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The route of administration determines how fast and how much drug reaches systemic circulation. Choice depends on the drug, desired onset, and patient condition.

Oral

Onset

30–60 min

Bioavailability

Variable (first-pass loss)

Examples: Most chronic medications

Pros

+Easy, safe, cost-effective
+Patient self-administer

Cons

−First-pass metabolism
−Slow onset
−Requires functional GI

Nursing

Check NPO status, swallowing ability, LOC
Never crush enteric-coated or extended-release tablets
Give with or without food per drug instructions

Sublingual / Buccal

SL / Buccal

Onset

1–5 min

Bioavailability

High (bypasses first-pass)

Examples: Nitroglycerin, ondansetron ODT

Pros

+Rapid onset
+Bypasses liver

Cons

−Limited drug selection
−Patient cooperation needed

Nursing

Instruct patient NOT to swallow or chew
Let dissolve completely under tongue or in cheek
No food/drink until dissolved

Intravenous

Onset

Immediate

Bioavailability

100%

Examples: Emergency drugs, antibiotics, fluids

Pros

+Fastest onset
+Precise titration
+Bypasses absorption

Cons

−Infection risk
−Infiltration / extravasation
−Rapid toxicity if error

Nursing

Verify IV site patency before each dose
Check drug compatibility with running fluids
Monitor site for redness, swelling, pain
Use correct infusion rate — pump for high-alert drugs

Intramuscular

Onset

10–20 min

Bioavailability

High

Examples: Vaccines, depot antipsychotics, ceftriaxone

Pros

+Faster than oral
+Depot formulations available

Cons

−Painful
−Risk of nerve injury
−Avoid in bleeding disorders

Nursing

Ventrogluteal preferred for adults (>1 mL)
Deltoid for vaccines (≤1 mL)
Vastus lateralis for infants
Use Z-track for irritating drugs (iron, haloperidol)

Subcutaneous

SC / SubQ

Onset

15–30 min

Bioavailability

High

Examples: Insulin, heparin, enoxaparin

Pros

+Patient can self-administer
+Slower, sustained absorption

Cons

−Limited volume (<1.5 mL)
−Lipodystrophy with repeated use

Nursing

Rotate sites (abdomen, thigh, upper arm)
Insulin: 90° angle (45° if thin)
Heparin: do NOT aspirate or massage
Pinch up skin in thin patients

Inhalation

INH

Onset

Seconds to minutes

Bioavailability

Local (lungs) + some systemic

Examples: Albuterol, fluticasone, ipratropium

Pros

+Direct to target organ
+Lower systemic dose

Cons

−Technique-dependent
−Oral candidiasis with ICS

Nursing

Teach proper inhaler technique; use spacer when ordered
Bronchodilator BEFORE corticosteroid
Rinse mouth after inhaled corticosteroids
Monitor peak flow if asthma

Transdermal

Patch

Onset

Hours to days

Bioavailability

Steady, sustained

Examples: Fentanyl, nicotine, nitroglycerin, estrogen

Pros

+Long duration
+Bypasses first-pass
+Steady levels

Cons

−Slow onset
−Skin irritation

Nursing

ROTATE sites; remove old patch before applying new
Document patch location and time
Apply to clean, dry, hairless skin
Wear gloves when handling fentanyl patches

Rectal

Onset

15–60 min

Bioavailability

Partial first-pass bypass

Examples: Acetaminophen, antiemetics, laxatives

Pros

+Useful when NPO or vomiting
+Local or systemic effect

Cons

−Variable absorption
−Patient acceptance

Nursing

Avoid in neutropenic or thrombocytopenic patients
Insert past internal sphincter (~1 inch in adults)
Position on left side

Key Pearls

IV = fastest onset, 100% bioavailability — no absorption phase
Sublingual bypasses first-pass metabolism (rapid systemic effect)
Transdermal gives steady, long-acting levels — great for chronic pain
Always match the route to the patient's clinical status (NPO, LOC, GI function)

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Disclaimer: PharmPal Nurse is for education only and is not medical advice. Do not use it to diagnose, treat, prescribe, or make patient-care decisions; always verify with current drug references, your instructor, facility policy, and a licensed provider. In emergencies, call local emergency services.