Drug Metabolism And Hepatic Circulation Flashcards
What are the blood supplies of the liver?
It receives blood from the left and right hepatic artery
Blood is brought back to the liver via the portal vein which comes from the intestine.
Where are drugs metabolised?
By liver hepatocytes
What is the order of drug exposure?
- Portal vein
- Liver sinusoids
- Hepatic vein
- Hepatic artery
- Common bile duct
What part of the gut isn’t drained by the portal vein?
Mouth to the lower third of oesophageal is drained straight into the systemic system.
What two drug administration routes avoids liver metabolism
Buccal and sublingual
Go straight into the systemic veins
(Possibly rectal)
How does first pass metabolism affect drug availability?
Drugs can be lost in the GI tract walls.
Drugs can be absorbed via the portal vein into the liver where is undergoes metabolism or biliary excretion.
What is bioavailability?
The fraction of a dose that reaches the systemic circulation unchanged.
What is the affect of first pass metabolism on bioavailability?
First pass metabolism reduces bioavailability.
What is the benefit of enterohepatic circulation of bile?
Enterohepatic recycling can delay elimination, Prolonging drug half life.
This can maintain clinical effect
Or increase the risk of side effects
What is phase 1 metabolism of drugs?
Cytochrome P450 enzymes =oxidation/ hydrolysis and hydration.
Phase 2 metabolism of drugs?
Conjugation, makes drugs more water soluble for elimination
How much of bile is reabsorbed into the bloodstream?
95%
