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Flashcards in Drug Distribution Deck (46)
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1

What must a drug do to be active

Leave the blood stream and enter the inter or intracellular spaces

2

What is drug distribution

The Reversible Transfer of a Drug between the Blood and the Extra Vascular Fluids and Tissues of the body (e.g. fat, muscle, and brain tissue)

3

What factors determine tissue distrubution

Plasma protein binding
Tissue perfusion
Membrane characteristics
Transport mechanisms
Diseases and other drugs (esp renal failure, liver disease, obesity)
Elimination

4

What type of membrane characteristics are there

Blood-brain barrier
Blood-testes/ovary barrier

5

Give examples of drugs which bind to proteins in plasma

Many drugs do this
Albumin
Alpha 1-glycoprotein (e.g. phenytoin)

6

In what sate are drugs biologically active

Unbound

7

Is plasma protein binding reversible

Yes

8

How can the amount of bound drug be changed

By:
Renal failure
Hypoalbuminaemia
Pregnancy
Other drugs
Saturability of binding

9

What parameters need to be characterised when considering therapeutic range

Volume of distribution
Clearance
Half-life

10

What is Vd

Apparent volume of distribution

11

What is volume of distribution

The volume of plasma that would be necessary to account for the total amount of drug in a patient's body, if that drug were present throughout the body at the same concentration as found in the plasma (L/kg)

12

What does it mean if the Vd is high

A high ability of the drug to diffuse into and through membranes

13

What is Cl

Clearance
The theoretical volume from which a drug is completely removed over a period of time

14

How is clearance measured

Measure of elimination in units of time (ml/min)

15

What is renal clearance dependent on

Concentration and urine flow rate

16

What is hepatic clearance dependent on

Metabolism and biliary excretion

17

What is half life (t1/2)

The time taken for the drug concentration in the blood to decline to half of the current value

18

Give an example of drug half life

If it takes 4 hours for the concentration of a drug in the blood stream to drop from 10mg/L to 5 mg/L then the half life is 4 hours

19

What does half life depend on

The volume of distribution and rate of clearance

20

What does the prolongation of the half life of a drug do

Increase toxicity of a drug because of a:
Reduction in clearance
Large volume of distribution (e.g. amiodarone)

21

What does the formula, t1/2 = 0.693Vd/Cl link together

The chemical properties of the drug, i.e. lipophilicity, and the ability of the body to metabolise and excrete the drug

22

How does knowledge of the half life of a drug help us clinically

Helps us to work out how often a drug needs to be administered

23

How should drugs be administered to have a therapeutic benefit

Depends on the half life
Long half life = less doses required
Short half life = more doses required

24

What can chronic administration cause

The plasma levels of a drug to take many doses before they stabilise, usually 4-5 half-lives
This may necessitate a loading dose

25

What is drug elimination

The removal of active drug and matabolites from the body
It determines the length of action of the drug

26

What is drug elimination made up of

Drug Metabolism
Drug Excretion

27

Where does drug metabolism normally take place

Liver

28

Where does drug excretion normally take place

Mainly kidney but also biliary system/gut, lung and breast milk

29

What mechanisms are used for drug excretion

Glomerular filtration
Passive tubular reabsorption
Active tubular secretion

30

About how many liters of fluid does the glomerulus filter a day

190