Drug Distribution Flashcards
What must happen for a trug to be considered active?
The drug must leave the bloodstream to the site of action
What factors affect drug distribution?
Tissue perfusion Elimination plasma protein binding Membrane characteristics disease
What membrane characteristics affect drug distribution?
Whether a drug is lipid soluble
Whether there is a active pathway for the drug
Whether there is a special barrier eg blood brain barrier
Is a drug active when it is bound or unbound?
Unbound
Is drug - protein binding reversible?
Yes
What factors affect protein drug binding?
Renal failure Drug-drug interactions Hypoalbuminaemia saturation Pregnancy
Define the apparent volume of distribution
The volume of drug that distributes around the body
What does a high volume of distribution mean?
A greater ability for a drug to diffuse through membranes
What is the theoretical volume of distribution?
40L
What would the volume of distribution be in a drug that does not penetrate cells?
12L
If a drug has a high rate of protein binding what would its volume of distribution?
3L
Define clearance?
Clearance is the theoretical volume which a drug is removed over a period of time
What is clearance a measure of?
Elimination
What is renal clearance dependent on?
Concentration of drug and urine flow rate
What is hepatic clearance dependent on?
Metabolism
Biliary excretion
Define drug half life
The time taken for the drug concentration in the blood in the blood to half
What factors affect half life?
Volume of distribution
Rate of clearance
What effect does prolongation of the half life for a drug have?
Increases drug toxicity
Why is it important to know a drugs half life?
To determine time between doses
How many doses of a drug are generally needed to achieve a steady state?
4-5
Define elimination
Removal of active drug in the body
What does drug elimination determine?
Length of action of the drug
What two factors affect elimination?
Metabolism
Excretion
What are the three principle mechanism used by the kidneys in drug excretion?
Glomerular filtration
Passive tubular reabsorbtion
Active tubular secretion
