Elimination and clearance

7 important questions on Elimination and clearance

What is the volume of distribution?

You measure the concentration in your fluid and from this you could calculate the amount of fluid.
For example you do not know the volume of the fluid, you can calculate the volume by knowing how many drug goes in and what the concentration is.

Lets say your body has a volume of 90 kg. When the volume of distribution is 90, the drug is more or less divided over the whole body. If the Vd in the plasma is 1000, you know it is not even spreaded.

What can be a negative side of a long half-life?

For example, diazepam is a sleeping drug with a half-life of 48 hours. This means that you  stay sleepy for the whole day because it breaks down really slowly. That is why oxazepam is more and more used. This is an acitvated state of diazepam with a half-life of 4 to 15 hours. Which makes it better as a sleeping drug.

What is the role of tissue protein binding on drug distribution?

Some drugs are highly bound to tissue proteins.
When a lot of drug bind to proteins in a tissue, there might be needed a larger dose to get the same effect. It also takes longer to break down the drug or remove it form the body.
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What is the role of plasma protein binding on drug distribution?

Some drugs are highly bound to plasma proteins. Acid drugs bind to albumin and basic drugs bind to alpha-acid glycoprotein. When drugs bind to plasma proteins the distribution out of the vascular compartment is limited and therefore more drug might be needed. Also it takes more time to remove the drug from the body

Which organs are mainly involved in the elimination of a drug?

Liver and kidney

Also skin, intestines and lungs can play a role.

What is extraction ratio?

Extraction ratio is the unit what is comming out. Never higher than 1

How is clearance connected to half-life?

First order:
The formula of Cl has a value that is dependent on the half-life.
This formula for Cl only applies when there is first order!

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