Drug Distribution

Question 1

What is definition of drug distribution?

Answer 1

Dispersion of drug among fluids + tissue of body

Question 2

Is there an absorption phase in I.V dose?

Answer 2

No

Question 3

Higher [drug] in blood = ………

Answer 3

Higher [drug] at sites of action

Question 4

What are the feature of 1st order kinetic of drugs?

Answer 4

Constant half life
Constant clearance
Constant fraction of drug is removed

Question 5

What are features of zero order kinetics of drugs?

Answer 5

Saturation kinetics
Clearance and half life fluctuate with [drug]
Constant amount of drug is removed

Question 6

Give examples of drugs that display zero order kinetics

Answer 6

Alcohol and phenytoin

Question 7

What is definition of half life?

Answer 7

Time taken for the [drug] to reduce by 1/2

Question 8

What does volume of distribution for drug indicate?

Answer 8

It indicates the extent of distribution for a drug

Question 9

What does elimination describe?

Answer 9

Describes activity of metabolising enzymes/excretion mechanisms
It Increases proportionally as doubling the [drug] doubles rate of elimination

Question 10

What does plasma clearance mean?

Answer 10

Volume of plasma cleared of drug per time (mlmin^-1)

Question 11

What is equation for clearance?

Answer 11

CL= rate of elimination/ [drug plasma]

Question 12

How are clearance and half life linked ?

Answer 12

The higher the clearance, the lower the half life

Question 13

What is bioavailability (F)?

Answer 13

It measures extent of absorption
It is fraction of drug in circulation compared to dose
It can be any value to one
1 being 100%
Higher the bioavailability, the higher the extent of absorption

Question 14

What is low bioavailability caused by?

Answer 14

Poor absorption
Chemical reactions at site of delivery
First pass metabolism

Question 15

What is choice of route of drug guided by?

Answer 15

Bioavailability 
Chemical properties of drug
Convenience
Need to control specificity of action 
Desired onset/duration/offset of action

Question 16

Multiple dosing leads to …….

Answer 16

‘Steady state’ where amount of drug absorbed equates the amount of drug eliminated

Question 17

For drugs with long half lives achievement of steady state can be accelerated by a …….

Answer 17

Loading dose (largest 1st dose) with maintenance dose (which replenishes what is lost in that time)

Question 18

What are general rules for achieving steady state?

Answer 18

Repeated dose of drug eventually produce a steady state concentration
Time to plateau is 4-5 x drug half life
Steady state levels are not actually flat
Fluctuation size is inversely proportional to number of daily doses
Fluctuations create potential for sub therapeutic treatment or toxicity
For drugs with long half lives achievement of steady state can be accelerated by loading dose