Drug Distribution Flashcards
Where does a drug have to go to be active?
Inter or Intracellular spaces.
What is drug distribution?
Reversible transfer of a drug between the blood and extravascular fluids and tissues.
What are the 6 tissue distributions?
Plasma protein binding Tissue perfusion Membrane characteristics Transport mechanisms Disease Elimination
Only bound/unbound drug is biologically active.
Unbound
Is binding reversible?
Yes
What are 5 factors which can affect amount of bound drug?
Renal failure Hypoalbuminaemia Pregnancy Other drugs Saturability
Define apparent volume of distribution (Vd)
Volume in which the amount of drug would be uniformly distributed to produce the observed blood concentration.
The greater the Vd, the ______ the ability of the drug to diffuse into and through membranes.
Greater
In theory, what should the Vd be?
42L
Define clearance.
Theoretical volume of fluid from which a drug is completely removed over a period of time.
In renal clearance, what is clearance dependent on?
Concentration
Urine flow rate
In hepatic clearance, what is clearance dependent on?
Metabolism
Biliary excretion
Define half life.
Time taken for the drug concentration in the blood to decline to half of the current value.
What does half life depend on?
Volume of distribution
Rate of clearance
Prolongation of the half life will ______ the toxicity of a drug.
Increase
To have a therapeutic benefit most drugs need to be given ______.
Chronically.
Define drug elimination.
Removal of active drug and metabolites from the body.
What are the primary organs for drug excretion?
Kidney
What are the 3 principal mechanisms of excretion?
Glomerular Filtration
Passive tubular reabsorption
Active tubular secretion
How many litres of fluid does the glomerulus filter per day?
190
Where are some drugs actively secreted?
Into the proximal tubule.
As filtrate moves down the renal tubule any drug present is ______.
Concentrated
Passive diffusion occurs in the ______ tubule.
Distal
The liver secrets _ litre of bile a day.
1
Biliary secretion accounts for -% of drug elimination.
5-95
Define entero-hepatic circulation.
Many drugs are reabsorbed from the bile into the circulation.
Metabolism in the liver often leads to ______ of the drug.
Conjugation
