A LITTLE LIGHTBULB MOMENT
Pharmacokinetics and pharmacodynamics
Bioavailability is the fraction reaching systemic circulation
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How much of the swallowed dose actually makes the bloodstream party
The idea behind the cue
Bioavailability is the fraction of an administered dose that reaches systemic circulation unchanged. It is 100% for IV dosing by definition and is often lower for oral dosing because of incomplete absorption and first-pass metabolism.
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Short & simple
How much of the swallowed dose actually makes the bloodstream party
Acronym
BIO — Bedazzled Impala Overreact.
Story
A suitcase of tablets leaves home, but some get lost at security, some spill in transit, and some are intercepted by liver customs. The portion that actually arrives unchanged in blood is the bioavailable share.
Connect the pieces
- B (Bedazzled) → Bioavailability: The fraction of an administered dose that reaches systemic circulation unchanged.
- I (Impala) → Intravenous: IV dosing is 100% bioavailable by definition because it bypasses absorption and first pass.
- O (Overreact) → Oral: Oral dosing is often less than 100% because absorption may be incomplete and first-pass metabolism can remove drug.
- Bedazzled · Bioavailability: The fraction of an administered dose that reaches systemic circulation unchanged.
- Impala · Intravenous: IV dosing is 100% bioavailable by definition because it bypasses absorption and first pass.
- Overreact · Oral: Oral dosing is often less than 100% because absorption may be incomplete and first-pass metabolism can remove drug.
Know the limits
Bioavailability is route-based; it is not the same as potency, efficacy, or clinical success.
Further reading · OpenStax Pharmacology for Nurses · foundational mechanisms ↗Check your understanding
A formulation study compares the portion of each administered dose recovered in systemic circulation as unchanged drug. Which measurement is the study describing?
A. The maximum effect a drug can produce
B. The fraction of a dose that reaches systemic circulation unchanged
C. The amount of drug bound to plasma proteins
D. The speed at which a drug is eliminated from plasma
Reveal explanation
The fraction of a dose that reaches systemic circulation unchanged
Bioavailability specifically refers to the fraction of dose reaching systemic circulation unchanged.
Further reading · OpenStax Pharmacology for Nurses · foundational mechanisms ↗