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Pharmacology: Pharmacokinetics: absorption and distribution · Routes of Administration and Absorption

How the route, the formulation and a drug's chemistry decide how quickly and how much of it reaches the blood.

For learning, not medical advice: for your own health, ask a doctor or another qualified professional.

Pharmacology · 26 questions

Try 3 questions

1. Which route of administration gives a drug 100% bioavailability by definition?

  1. Sublingual tablet
  2. Intravenous injection
  3. Intramuscular injection
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Answer: Intravenous injection

Bioavailability is the fraction reaching systemic circulation, and an IV dose is placed there directly, so nothing is lost to absorption.

2. How do most oral drugs cross the cells lining the gut?

  1. Uptake by intestinal immune cells
  2. Passive diffusion of the uncharged form
  3. Active pumping of the charged form
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Answer: Passive diffusion of the uncharged form

Most drugs are small lipophilic molecules that diffuse down their concentration gradient through cell membranes, and only the un-ionized form crosses the lipid bilayer easily.

3. Aspirin, a weak acid, is mostly un-ionized in the stomach, yet most of it is absorbed in the small intestine. Why?

  1. Stomach acid destroys aspirin first
  2. Only the intestine has drug transporters
  3. The intestine's far larger surface area
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Answer: The intestine's far larger surface area

The small intestine's villi and microvilli give it an enormous surface area and long contact time, which outweighs the less favorable ionization there.

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