Drug Absorption

Question 1

Define Pharmaceutical process

Answer 1

Get the drug into the patient

Question 2

Define Pharmacokinetic process

Answer 2

Get the drug to the site of action

Question 3

Define Pharmacodynamic process

Answer 3

Produce the correct pharmacological effect

Question 4

Define Therapeutic process

Answer 4

Produce the correct therapeutic effect

Question 5

What determines drug pharmacokinetics

Answer 5

Absorption
Distribution
Metabolism
Elimination

Question 6

What are the methods of administration?

Answer 6

Oral
Intravenous
Subcutaneous
Intramuscular
Other GI - Sublingual, rectal
Inhalation
Nasal
Transdermal

Question 7

What is absorption?

Answer 7

the process of movement of unchanged drug from the site of administration to the systemic circulation.

Question 8

What does ADME allow?

Answer 8

understanding of:
Dosage
Drug administration
Drug handling
Patient variability
Potential for harm.

Question 9

What is sublingual?

Answer 9

Under the tongue

Question 10

What is Tmax? Oral absorption

Answer 10

The time to peak concentration, important in relieving pain

Question 11

What is Cmax? Oral absorption

Answer 11

The peak concentration, important in determining a toxic dose

Question 12

What is the (AUC)? Oral absorption

Answer 12

The area under the drug concentration-time curve

Question 13

Does the dose effect the tmax?

Answer 13

No, alters cmax

Question 14

What does the The area under the drug concentration-time curve represent?

Answer 14

The amount of drug which reaches the systemic circulation

Question 15

What is the Theraputic range?

Answer 15

The range of concentrations at which a drug is active.

Question 16

What happens above or below the theraputic range

Answer 16

Toxicity

Insufficient pharmalogical action

Question 17

What does The AUC allows us to estimate?

Answer 17

The amount of drug which reaches the circulation and which is available for action
BIOAVAILABILITY - Used to compare routes of administration

Question 18

What is the bioavailability of an intravenous drug?

Answer 18

100%

Question 19

What are the factors affecting Bioavailability? (oral absorption)

Answer 19

Formulation -
Slow release preparations

Ability of drug to pass physiological barriers
-Particle size
-Lipid solubility
-pH and ionisation

Gastrointestinal effects
-Gut motility
-Food
-Illness

First pass metabolism (whereby the concentration of a drug is greatly reduced before it reaches the systemic circulation.)

Question 20

What is dissolution?

Answer 20

The rate a drug breaks up

Question 21

What is an example of a physiological barrier?

Answer 21

Transport across membranes

Question 22

What are the methods of transport across membranes?

Answer 22

Passive diffusion
Filtration
Bulk flow
Active transport
Facilitated diffusion
Ion-pair transport
Endocytosis

Question 23

What does the degree of the ionisation of the drug depend on?

Answer 23

As most drugs are weak acids or bases the degree of ionisation depends on the pH of the environment

Question 24

What form of the drug crosses the membrane?

Answer 24

The unionised form

Question 25

What is the distribution of the un-ionised form of a drug?

Answer 25

Should distribute across the membrane until equilibrium is reached - equal concentration on each side.

Question 26

Where will an acidic drug be most concentrated?

Answer 26

In the compartment with high pH

Question 27

What does the Henderson-Hasselbalch equation describe?

Answer 27

The relationship between the local pH and the degree of ionisation

Question 28

What is The ability of a drug to diffuse across a lipid barrier is expressed as?

Answer 28

lipid-water partition coefficient

Question 29

What is the lipid-water partition coefficient?

Answer 29

The ratio of the amount of drug which dissolves in the lipid and water phase when they are in contact.

Question 30

Describe passive diffusion

Answer 30

Very common. Occurs along concentration gradient. Non selective Not saturable Requires no energy No carrier is needed Depends on lipid solubility and degree of ionsation

Question 31

Describe Active Absorption

Answer 31

Relatively unusual. Occurs against concentration gradient. Requires carrier and energy. Specific Saturable. Iron ,K , Na , Ca Uptake of levodopa by brain Energy dependant

Question 32

What is the structure of drugs that undergo active transport?

Answer 32

They must resemble naturally occurring compounds

Question 33

Describe facilitated diffusion

Answer 33

Occurs along the concentration gradient Require carriers Saturable Structure specific No energy required Mixed order kinetics monosaccharides, amino acids, vitamins

Question 34

Where does filtration occur?

Answer 34

Through channels in the cell membrane.

Question 35

What is the milecular size of the drug in Filtration / Bulk Flow/ Pore Transport?

Answer 35

Low molecular size

Question 36

What is the driving force in Filtration / Bulk Flow/ Pore Transport?

Answer 36

Hydrostatic or the osmotic pressure difference across the membrane.

Question 37

What does the speed of gastric absorption affect?

Answer 37

speed at which drug reaches site of absorption

Question 38

What is the effect of food on absorption?

Answer 38

Can enhance or impair rate of absorption

Question 39

How does illness affect absorption?

Answer 39

Malabsorption (eg Coeliac disease) can increase or decrease rate of absorption Migraine reduces rate of stomach emptying and therefore rate of absorption of analgesic drugs.

Question 40

Decribe the Subcutaneous / Intra-muscular route of administration?

Answer 40

Needs small volume Avoids first pas metabolism

Question 41

Describe Sublingual, Buccal administration

Answer 41

Sublingual absorption from the buccal mucosa bypasses first pass metabolism which will inactivate the drug. Drugs given this way enter the circulation directly i.e. GTN for angina

Question 42

Describe rectal administraion

Answer 42

Bypass first pass metabolism. Absorption tends to be slow. The rectum is often used for drugs which cause irritation of the stomach.

Question 43

Describe the benefits of inhalation/nasal administration

Answer 43

Relatively rapid action Avoids problems with oral absorption Although only 5-10% absorbed

Question 44

Describe Transdermal absorption

Answer 44

Avoids first pass metabolism. Can provide controlled release. Few substances well absorbed. Need to be non-irritant.