The one compartment model Flashcards
In pharmacokinetics, what is the body considered as? What are the constituents of it?
A single compartment
Volume: volume of distribution
All of the drug is dumped into this volume- IV bolus
What are the 2 assumptions of the one-compartment model?
1) Any drug within the compartment is distributed evenly and instantaneously (well-stirred)
- Not realistic due to there being some time for the blood to go around the whole body
2) The volume remains constant during the period under study
- Not realistic because there is a constant fluid shift in the body (dehydration)
What are pharmacokinetic factors make up elimination?
Elimination = metabolism + excretion
What order is the rate of elimination?
First order
It is directly proportional to the amount of drug in the body
What equation shows the difference in the amount of drug in the body and the direct proportionality of elimination?
dAb/dt = -ke × Ab Ab= amount in body
What is ke and why is it negative?
The constant of elimination
It is negative because the drug is being excreted. Drug is taken out of the one compartment model
How is eliminaton rate expressed using clearance?
C= C0 x e^(-ke x t) t= time ke= elimination constant C0= initial concentration
How are the 2 steps to estimating the parameters?
- Administer IV
- Concentration is measured multiple times
How can clearance be shown in log form? Why can this be presented as a graph?
ln C= ln (C0 ) - (ke x t)
This is in the form y= mx+ c where ke is the gradient of the line
How does amount of drug in the body relate to the area under the graph?
dAb/dt = -Cl x C
dAb = -Cl x C x dt
C x dt is the are under the graph as this is the integral of C over the time dt
What is the final equation linking dose and area under the curve?
Dose= Cl × AUC_0^∞
Why does total elimination equal to the dose
We can’t eliminate more than what is given
