3) Pharmacokinetics and Pharmacodynamics

Question 1

What is Bioavailability (F) ?

Answer 1

The fraction of drug which reaches circulation unaffected.

IV drug = 100%

Question 2

What factors can affect F

Answer 2

> Absorption
- Formulation 
- Age (Luminal Changes)
- Food 
- Vomiting / Malabsorption 
> 1st Pass Metabolism 
Drug metabolised before reaching systemic circulation

Question 3

What factors can affect protein binding of drugs ?

Answer 3

> Hypoalbuminaemia
Pregnancy
Renal Failure

Question 4

What are factors that can affect therapeutic agents ?

Answer 4

> Blood flow 
> Capillary Structure 
> Lipophilicity / Hydrophilicity
> Protein Binding 
> Volume of Distribution

Question 5

What is Volume of Distribution ?

Answer 5

A measure of how far the drug will distribute in the body.
Small Vd = Drug is confine to plasma and extracellular fluid
Large Vd = Drug is distributed throughout tissue

Vd = Dose / [Drug]plasma

Question 6

What factors can affect Vd ?

Answer 6

> Weight 
- Drugs can travel through fat better, meaning there is less drug in the plasma 
> Blood Flow 
> Drug Interactions 
> Receptor Sites.

Question 7

What does Phase I enzymes do in metabolism ?

Answer 7

They carry out the first step of metabolism in the liver.
Usually carried out by CYP450 enzymes 
> Oxidation 
> Dealkylation 
> Reduction 
> Hydrolysis

Question 8

What does Phase II enzymes do in metabolism

Answer 8

They add components such as:
> Sulfates 
> Glutathione 
> Glucuronide 
> N - Acetyl

Question 9

What factors can affect Metabolism of a drug

Answer 9

> Inhibition of CYP450 enzymes such as grape fruit 
- Drugs last longer 
> Liver Disease 
> Age
> Hepatic Sate 
> Alcohol

Question 10

What are pro drugs ?

Answer 10

Drugs that are activated when they are metabolised

e.g. Codeine -> Morphine

Question 11

What are the different routes for the Elimination of Drugs ?

Answer 11

> Kidney (Major)
> Fluids 
- Sweats
- Tears
- Genital Secretions
- Saliva 
- Breast Milk 
> Solid 
- Faeces 
- Hair 
> Gases

Question 12

What factors affect Elimination of a drug ?

Answer 12

> Renal Disease
-> Reduced GFR
Hepatic Disease
-> Reduced Liver Activity = Less metabolism so less elimination
Cardiac Disease
-> Reduced Organ Perfusion to liver and kidney

Question 13

What 3 processes affect Kidney Elimination ?

Answer 13

1) GFR
2) Tubular Secretion
3) Tubular Re absorption

Question 14

What is a Half Life ?

Answer 14

The amount of time it takes for the concentration of the drug to reduce by half.
t1/2 = 0.693 x Vd / Cl

Question 15

Describe First Order Kinetics

Answer 15

Rate of Elimination is proportional to the Drug Level
Half life can be easily be determined.
(Most Drugs exhibit first order kinetics at therapeutic doses)

Question 16

Describe Zero Order Kinetics

Answer 16

Rate of Elimination of constant
(At high enough concentrations all drugs exhibit at high [])
These drugs are more likely to result in toxicity b/c you are now unable calculate their t 1/2

Question 17

How many half lives is required before a steady state is reached ?

Answer 17

4 / 5

Question 18

What is a steady state (Css)

Answer 18

When the plasma concentration is in the therapeutic window

Question 19

How can we achieve the steady state of a drug without waiting for 4 / 5 half lives ?

Answer 19

Give a loading dose,this is when you give a larger dose than normal for the first few times
Loading dose = Vd x [Drug] Target