first past metabolism in pharmacology?

Question

absorbtion, distribution and excretion

Answer 1

First pass metabolism occurs when a drug is taken orally and is absorbed through the gut (GI tract). Many drugs are absorbed into the portal blood stream and taken through the liver BEFORE they enter the main circulation (most of the blood coming from the GIT has to go through the liver). This way, the liver has a chance to metabolise toxins (and medicines) before it effects our body.

Opiates, for example morphine, are metabolised extensively in the liver. Giving 10mg oral morphine will mean that only about 3mg reaches the main circulation of the body. This corresponds to a 30% bioavailability.

Here are some pharmacology links that you should read so you can understand the terms.

Absorption relates to how the drug is taken up into the body.
Distribution describes which compartments of the body the drug enters and the time frame taken to do this
Excretion is the means by which the drug is eliminated from the body - primarily through the kidneys (into the urine) - or by metabolism in the liver and sometimes excretion into the bile and hence into the faeces.