First-pass metabolism and prodrugs
Explains why some drugs don't work orally — and why others only work after being metabolized.
Where this fitsConnects to 2 · Unlocks 1
- Connects to
- Absorption and routes of administration — Oral drugs pass through gut and liver before the brain.
- When enzymes change: induction, inhibition and genetics — Inhibiting the first-pass enzyme changes everything.
- Unlocks
- Half-life and redistribution — With delivery understood, turn to how long drugs last.
Orient
Prodrug – chemical is not initially psychoactive, but active metabolite of chemical is. First-pass metabolism – drug passes through GI tract and/or liver before it reaches brain, causing some amount of the drug to be broken down; this effectively lowers bioavailability. More direct routes into the bloodstream (IV, inhalation, intranasal, sublingual) avoid it.
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.
- Prodrug
“Chemical is not initially psychoactive – but active metabolite of chemical is”Slides 04, p. 41
e.g., psilocybin → psilocin; lisdexamfetamine (Vyvanse) → amphetamine.
- First-pass metabolism
“Drug passes through GI tract and/or liver before it reaches brain, causing some amount of the drug to be broken down (metabolized)”Slides 04, p. 42
“This effectively lowers bioavailability of the drug – sometimes massively!”
From your course: Course slides 04, pp. 41–43
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Full lesson: Prodrugs and first-pass metabolism