CPT1: Distribution Flashcards
What is distribution defined as?
The reversible transfer from the drug in the blood stream to other areas of the body
What is the rate and extent of distribution determined by?
- How well perfused organs/ tissues are
- binding of drugs to plasma proteins and tissue compartments
- permebaility of the tissue to the drug
- ion trapping
- p-GP
- pKa
What are pateint factors which effect drug distribution?
- odema - weight loss
- gender
- ethnicity
- pregnancy
- age
- health status
Where is the most blood distibuted too?
- liver
- kidneys
What is protein binding?
When a drug binds to a protein in the blood so can’t penetrate tissues OR if a drug binds to a protein in the tissue and can’t leave
What is ion trapping?
The pH of the stomach is acidic and the pH of blood is neutral.
e.g. an acidic drug can move easily across into blood as it is unionized. However will become more ionized in the blood therefore little can move back into the stomach.
Acidic drugs accumulate in basic enviroment, where as basic drugs accumulate in acidic enviroments
In reference to the parmacokinetics model, what is a compartment?
The sum of all tissues into which a drug distributes into at approx the same rate
Describe single compartment
- All tissues penetrated rapidly or none at all
- Combine blood and all tissues as a single compartment
- Drug assumed to spread instantly throughout all space
Describe two compartment model
- Drug penetrates some tissues rapidly and others slowly
- Combine blood and tissues (T1&2) as first compartment. Drug spreads instantly into this compartment
- Compine tissues3&4 as second compartment
What are the units of:
- Concentration
- elimination rate
- clearance rate
- mg/L
- mg/h
- L/h
What is volume of distibution?
The amount of drug required to keep the drug in the body at the same concentration as the drug in the plasma
What compartments may drug distribute into?
- Plasma (4L)
- Interstitial fluid (10L)
- intracellular fluid (28L)
NOT Q: Information about Vd
Vd describes how well a durg is removed from the plasma and distributed to tissue. It doesn’t provide specific info on where drug is or whether it has concentrated in a particular organ.
Theoretical volume
What does a large and small Vd mean?
Large - wide distribution of drug or extensive protein binding
Small - protein binding or trapped in plasma
What equation is used to calculated Vd?
Vd = D/C
D= dose
C= conc
