First-pass effect

Definition

The first-pass effect is the rapid uptake and metabolism of an orally administered drug by the liver before it reaches systemic circulation. This process significantly reduces the bioavailability of the drug.

5 Must Know Facts For Your Next Test

1. The first-pass effect primarily occurs in the liver, but can also involve the gastrointestinal tract.
2. Drugs with a high first-pass effect require higher oral doses or alternative routes of administration to achieve therapeutic levels.
3. Sublingual and intravenous (IV) routes bypass the first-pass effect, leading to higher bioavailability.
4. Prodrugs are sometimes designed to take advantage of the first-pass effect for activation into their active forms.
5. First-pass metabolism can be influenced by factors such as age, liver function, and concurrent use of other medications.

Review Questions

• What organ is primarily responsible for the first-pass effect?
• How does the first-pass effect influence drug bioavailability?
• Which routes of administration can bypass the first-pass effect?

Related terms

Bioavailability:

The proportion of a drug that enters circulation when introduced into the body and can have an active effect.

Prodrug: A medication or compound that is metabolized into a pharmacologically active drug after administration.

Metabolism:

The chemical processes within a living organism that maintain life, including how drugs are processed in the body.