Pharmacology

Question 1

Define Volume of Distribution

Answer 1

A proportionality factor that relates the amount of drug in the body to the concentration of drug measured in the plasma. Vd = Amount of drug in body/Concentration of drug in plasma

Question 2

What is Pharmacokinetics?

Answer 2

The mathematics of the time course of absorption, distribution, metabolism and excretion of drugs in the body. This determines the plasma concentration of a drug.

Question 3

Why do we calculate PK parameters?

Answer 3

Factors such as age, drug interactions, disease state and pharmacogenomic profile affect the rates of metabolism and excretion. The study of PK enables clinicians to individualise a dosing regiment for a patient

Question 4

what is Kel

Answer 4

The fraction of drug eliminated per unit of time

Question 5

What is a first order kinetics concentration-time curve like?

Answer 5

Rate of metabolism is proportional to the plasma drug concentration
Half life is constant

Question 6

Importance of zero-order kinetics

Answer 6

Rate of metabolism is independent of plasma drug concentration.
rate of metabolism is constant but half life is not
drugs can build up in the body and cause toxic side affects

Question 7

Why is Volume of distribution important?

Answer 7

It is used to calculate drug dose
Plasma concentration is affected by the Vd of a drug
High Vd means drug accumulates in peripheral tissue and there is low plasma concentration
Low Vd means a high plasma concentration of drug

Question 8

What is C0?

Answer 8

The initial concentration of drug in the plasma at time=0 when the dose is administered as an IV injection

Question 9

equation linking Vd, dose and C0?

Answer 9

Vd= Dose/C0

Question 10

How to calculate C0 from a concentration time graph?

Answer 10

Extrapolate the line and read the value for when T=0 (crosses the Y axis)

Question 11

What is the half life of a drug?

Answer 11

The time taken for the plasma concentration of the drug to half

Question 12

What is the clearance of a drug?

Answer 12

The volume of plasma cleared of a drug per unit time
The clearance of drugs is the PK parameter which most significantly limits the time course of action of a drug

Question 13

Equation for clearance

Answer 13

Cl= (0.693/half life) X Vd

Question 14

What is repeated dosing and steady state?

Answer 14

Often multiple doses are needed to provide a relative constant plasma concentration of drug
Steady-state is the equilibrium point where the amount of drug administered exactly replaces the amount of drug excreted.

Question 15

What is an optimal therapeutic dosing regimen?

Answer 15

One which seeks to maintain steady-state plasma drug concentration within the therapeutic window for that drug

Question 16

Equation for steady-state (Css)

Answer 16

Css= (Bioavailability X dose)/(interval dosing X clearance)

Question 17

Link between half life and steady-state

Answer 17

The shorter the half-life the more rapidly steady state is reached

Question 18

steady-state of drugs with a long-half life

Answer 18

For drugs with a long half life the drug will accumulate and chronic dosing is designed to achieve the therapeutic range at steady state

Question 19

What is Chronic dosing ?

Answer 19

Long interval over long time period

Question 20

What is loading dose?

Answer 20

Vd X desired Css (steady state plasma concentration)

Question 21

What is polymorphic expression and how does to influence response to a drug?

Answer 21

A slight genetic difference between individuals which alter how well the drug metabolising enzymes functions
this can result in increased/decreased enzymes activity and levels of metabolism

Question 22

What are fast metabolisers?

Answer 22

possess wild type enzyme which has normal activity
there are lower plasma concentration of parent drug and higher concentrations of metabolite
usually a normal therapeutic response

Question 23

What are slow metabolisers?

Answer 23

possess a defective enzyme which has reduced/no activity
high plasma concentration of parent drug and low concentrations of the metabolite
can lead to exaggerated therapeutic response and so a reduction in drug dose may be necessary

Question 24

what occurs in a person who has a liver disease?

Answer 24

capacity to uptake and metabolism lipid soluble drugs is reduced
first pass metabolism is reduced and so the bioavailability may be much greater
therefore the drug dose may need to be reduced

Question 24

what occurs in a person who has a liver disease?

Answer 24

capacity to uptake and metabolism lipid soluble drugs is reduced
first pass metabolism is reduced and so the bioavailability may be much greater
therefore the drug dose may need to be reduced

Question 25

what occurs in a person who has a cardiac disease?

Answer 25

in cardiac failure there is reduced blood flow and so reduced clearance and so there are supratheraputic drug levels
the drug dose may need to be decreased

Question 26

what occurs when there is a reduced glomerular flow rate in newborns, elderly, kidney/heart disease?

Answer 26

less drug is filtered
longer lasting drug action in the body
decrease the drug dose or increase dose interval

Question 27

What factors does pharmacodynamics depend on?

Answer 27

concentration of drug at the receptor
response at the receptor
postsynaptic response within cells

Question 28

what is the blood brain barrier

Answer 28

A network of blood vessels and tissue that is made up of closely spaced cells and helps keep harmful substances from reaching the brain

Question 29

How does age alter pharmacodynamics?

Answer 29

drugs acting on CNS produce an exaggerated response - blood brain barrier is less effective
response to B-adrenoreceptor drugs may diminish
baroreceptor sensitivity reduces

Question 29

How does age alter pharmacodynamics?

Answer 29

drugs acting on CNS produce an exaggerated response - blood brain barrier is less effective
response to B-adrenoreceptor drugs may diminish
baroreceptor sensitivity reduces

Question 30

What is tolerance?

Answer 30

the reduction in response to a drug after repeated administration