Absorption and routes of administration

Explains why route changes speed, peak and risk — the same drug can be gentle or dangerous depending on how it enters.

Where this fitsConnects to 1 · Unlocks 2

Connects to: The course lens: biopsychosocial, and no 'chemical imbalance' — Coca leaves vs cocaine vs crack is a route story.
Unlocks: First-pass metabolism and prodrugs — Oral routes pass the liver first — first-pass metabolism.
Half-life and redistribution — Route shapes the rise; half-life shapes the fall.

Orient

Enteral routes – gastrointestinal tract (GI) involvement: oral and rectal. Parenteral routes – no GI tract involvement: injection, inhalation, transdermal, and absorption through mucous membranes (sublingual, intranasal). Bioavailability depends on the drug and route: surface area, the drug’s acidity (pKa) versus local pH, and lipid solubility.

Course terms

Your professor's wording, word for word from the slides. Learn the term and this definition — the explanation underneath is only there to help it make sense.

Enteral routes: “Enteral routes – gastrointestinal tract (GI) involvement”Slides 04, p. 7
Oral and rectal.
Parenteral routes: “Parenteral routes - no GI tract involvement”Slides 04, p. 7
Injection, inhalation, transdermal, mucous membranes.
pKa and pH: “Based on similarity between strength of the drugs’ acidity (pKa) and local pH of absorption area”Slides 04, p. 5
e.g., a drug with pKa 8 absorbs better in the intestines (pH 7) than the stomach (pH 1).
Rectal: “Can sometimes increase bioavailability of drug vs. oral”Slides 04, p. 9
Because it bypasses gastric enzymes.
Inhalation: “Fastest route to the brain (even faster than injection!)”Slides 04, p. 10
Large lung surface area; pulmonary capillaries carry drug straight to the heart and brain.
Insufflation: “If specifically “snorting” a powder – insufflation”Slides 04, p. 12
Intranasal = absorbed through membranes of nasal passages.
Sublingual / buccal: “Absorbed through membranes of mouth, under tongue (sublingual) or gum/cheek tissues (buccal)”Slides 04, p. 14
e.g., nicotine gum, sublingual buprenorphine + naloxone (Suboxone).
Transdermal: “Absorbed through the skin (specifically the dermis) into plasma”Slides 04, p. 15
Patches: continuous, controlled release — “low and slow”.
Intravenous (IV): “Most dangerous route when not administered by medical professional”Slides 04, p. 17
100% bioavailability, fast onset, no dosage feedback until too late.
Intramuscular (IM): “Drugs injected into skeletal muscle”Slides 04, p. 18
Type 1: aqueous solution, rapid onset/short duration. Type 2: oily solution, slow onset/prolonged duration.
Depot injection: “Depot injections for extended release”Slides 04, p. 18
The oily (Type 2) IM injection.
Subcutaneous: “Injected in fatty tissues under skin and above muscle”Slides 04, p. 19
Implants can last a month or more.

From your course: Course slides 04, pp. 5–19

Tip: the ← and → keys move through the lesson.

Full lesson: Absorption and bioavailability · Oral and rectal administration · Inhaled and mucosal routes · Skin delivery and injection routes