PHARM - Pharmacokinetics - Drug Absorption and Distribution - Week 1 Flashcards
Define pharmacokinetics.
The process of getting drugs to and from their sites of action.
What are 4 key questions that are asked for clinical drug use?
What form is the drug in?
Where do you put it?
How much do you use?
How often do you use it?
Define administration.
Giving the drug to a recipient.
Define absoprtion.
The drug entering circulation.
Define distribution.
The drug spreading throughout the body.
Define elimination.
The removal of the drug from the body.
Name 4 factors that can influence the choice of route of administration.
Patient convenience - oral/rectal/injection
Cost
Bioavailability
Local vs systemic effect
Define local and systemic administration (4).
Local
-drug exerts effect at or near administration site
-access to limited tissue
Systemic
-drug enters the bloodstream
-will access many tissue
What limits drug access to tissue with local administration?
Absorption
What determines drug access to tissue with systemic administration?
Distribution
How can the side effects of a locally administered drug be reduced?
By choosing a concentration so that if a drug is absorbed, it is too low to cause systemic effects.
What kind of administration route does not require the drug to be absorbed?
Intravenous injection only. All others require absorption.
What is drug distribution driven by?
Circulation
Is drug distribution uniform?
No, its rarely uniform.
How does drug molecular size affect drug distribution?
Smaller molecules cross the vascular endothelium easier
How does a drug’s ability to bind plasma proteins affect drug distribution?
Unbound drugs will cross the vascular endothelium easier.
How does a drug’s lipid solubility affect drug distribution?
More lipid solubility will allow wasier easier crossing through cell membranes.
What happens when a drug’s lipid solubility is very high?
It will be sequestred in lipids (like adipose tissue).
Define volume of distribution.
Volume of body water in which a drug appears to be dissolved in after it has distributed throughout the body.
Describe the formula for volume of distribution.
Vd = X / C
X = amount in the body
C = concentration in the plasma
Vd is an apparent volume
Describe what happens to drugs with a small Vd vs a high Vd, and what concentration in the plasma would be like.
Small Vd - drug binds to plasma proteins, and plasma concentration is higher.
High Vd - drug binds to tissue/taken up by cells, and concentration in plasma is lower.
What does volume of distribution tell you?
How much drug will give a particular concentration of drug in the plasma.
Use the formula for volume of distribution to demonstrate how it can be used to calculate a dose of a drug to result in a desired concentration within the body.
X = Vd * C
Therefore, X is the dose of the drug administered via IV to give a desired plasma concentration C.
