Pharmacokinectics 1

Question 1

What factors affect drug response in patients?

Answer 1

 Pharmacokinetic factors ( e.g. differences in
absorption, distribution, metabolism & excretion)
 Pharmacodynamic factors ( e.g. differences in
receptor sensitivity, altered homeostatic
mechanisms )
 Interactions with other drugs
 Personality, beliefs

Question 2

What do you do once you have diagnosed a patient?

Answer 2

Choose the appropriate drug for the
required effect
Decide on the appropriate dose and
dosage interval

Question 3

What is the goal of drug therapy?

Answer 3

 Getting the chosen drug:
• into the appropriate tissue
• at the appropriate concentration
• for the appropriate length of time

So…
Good chance of achieving the desired
therapeutic effect

Question 4

How do you overcome the variable relationship between dose and effect?

Answer 4

Measuring the drug conc in the body can
help towards a more rational dose
• At steady state, plasma conc gives a relatively good index of conc at the receptor site
• Much less variation between conc & effect than between dose & effect

Question 5

What does drug disposition in the body allow you to do?

Answer 5

Allows you to understand the relationship between concentration and effect. It helps remove the variability regarding the different excretion methods.

Question 6

What is the definition of pharmacokinetics?What parameters does it connect?

Answer 6

dose rate and concentration in plasma

Question 7

What parameters does pharmacodynamics connect?

Answer 7

concentration and effect

Question 8

What are the concentration parameters in plasma?

Answer 8

There must be a minimum effective 
concentration (MEC)
There must be a maximum 
concentration
Equally there is a toxic concentration for 
many drugs

Question 9

What does Concentration-Response relationship for hypothetical drug do?

Answer 9

Allows you to define range of beneficial drug

Question 10

Define therapeutic range?

Answer 10

The concentration range which has
the highest probability of giving the
desired response with the minimum
of side effects

Question 11

Why pharmacokinetics ?

Answer 11

A knowledge of PKs allows more
rational dosing
Helps overcome the interpatient
variability in drug disposition

Question 12

How do you know what the rational drug dose rate should be?

Answer 12

measure the distribution and rate of elimination. The r=target concentration in the body should be the distribution volume.

Question 13

Define distribution

Answer 13

Distribution is the reversible movement of drug

between body compartments

Question 14

What is the apparent volume of distribution?

Answer 14

The apparent volume of distribution is that
volume that the drug must be dissolved in, to
give a conc equivalent to that found in
plasma.
For most drugs, it is not a physiological
volume, but gives some indication of
distribution out of plasma and tissue uptake.

Question 15

how much water is in the body?

Answer 15

Total Body Water (60% of body weight) ~ 42 L

Question 16

how much water is in the different body compartments?

Answer 16

• 2/3 of TBW in intracellular fluid space ~ 28 L
• 1/3 of TBW in extracellular fluid space ~ 14 L
Adult blood volume: ~ 5L
Adult plasma volume: ~ 3L

Question 17

What is the equation for loading dose?

Answer 17

Target conc ( mg / L ) x V ( L ) (volume of distribution)

Question 18

What is steady state concentration determined by?

Answer 18

clearance of drug and drug input