Drugs 1: Drug Absorption

Question 1

What 4 basic factors determine pharmacokinetics?

Answer 1

Absorption, Distribution, Metabolism, Elimination

= ADME

Question 2

What are the main reasons for studying pharmacokinetics? (3)

Answer 2

1. individualise patient therapy
2. monitor medication with a narrow therapeutic index
3. decrease the risk of adverse drug reactions while maximising pharmacological response to medication

Question 3

What are the 8 main ways of administering drugs to enter the bloodstream?

Answer 3

1. oral
2. intravenous
3. transdermal
4. subcutaneous (injection under skin)
5. nasal
6. inhalation
7. other GI (sublingual/under tongue or rectal)
8. Intramuscular

Question 4

What is a common condition treated by sublingual drugs? (under the tongue)

Answer 4

Angina

Question 5

What is the definition of absorption?

Answer 5

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

Question 6

What is in correlation with a plasma concentration of a drug?

Answer 6

Therapeutic response

Question 7

What are the 2 most important issues to consider when giving an oral drug?

Answer 7

1. amount of drug which enters the systemic circulation

2. speed at which it happens

Question 8

What is Tmax?

Answer 8

Time taken to peak concentration

Question 9

What is Cmax?

Answer 9

Peak concentration

Question 10

How does a quicker rate of absorption affect Tmax?

Answer 10

the earlier the drug concentration peak (Tmax will be reached quicker)

Question 11

What effect does increasing dosage of a drug have on the Tmax?

Answer 11

No effect (it affects the Cmax; concentration of the drug)

Question 12

What does the area under the curve represent? (the AUC)

Answer 12

How much of the drug reaches the systemic circulation over a period of time

Question 13

What is the therapeutic range?

Answer 13

Wide range over which a drug is active in

Question 14

What will happen if a drug is below and above a therapeutic range?

Answer 14

below: NO sufficient or pharmacological action
above: toxicity occurs

Question 15

What is a therapeutic index?

Answer 15

Measure of the range at which the drug is safe and active (works best in the middle region)

Question 16

What does the AUC allow us to estimate?

Answer 16

Allows us to estimate the amount of drug which reaches the circulation and which is available for action(bioavailability)

Question 17

What is the term which describes what amount of the drug reaches circulation and is available for action?

Answer 17

Bioavailability

Question 18

Why do intravenous drugs have very high peak levels?

Answer 18

There is 100% guarantee all of the drug will enter the body unlike rectal or oral

Question 19

What 4 factors affect bioavailability? (not including disease state)

Answer 19

1. formulation (drugs)
2. ability of drug to pass physiological barriers (particle size, lipid solubility, pH and ionisation)
3. gastrointestinal effects (gut motility, food, illness)
4. First pass metabolism (how fast the drug is metabolised, if fast then may not reach bloodstream in time)

Question 20

What does dissolution mean?

Answer 20

Breakdown of tablet in the stomach

Question 21

What is the main membrane drugs cross in terms of physiological barriers?

Answer 21

Small intestine/ bowel

Question 22

What are the 4 possible mechanisms involved in transport across physiological barriers?

Answer 22

1. passive diffusion
2. bulk flow
3. filtration
4. active transport (facilitated diffusion, ion-pair transport, endocytosis)

Question 23

Why do most drugs not completely ionise in water?

Answer 23

As they are weak acids and bases

Question 24

Are both ionised and un-ionised forms of drugs present?

Answer 24

Yes

Question 25

Do ionised drugs cross cell membranes?

Answer 25

NO, ionised drugs do not cross cell membranes

Question 26

Do un-ionised drugs cross cell membranes?

Answer 26

Yes- they unionised drugs distribute across the membrane until equilibrium is reached (equal concentration of drug on both sides)

Question 27

Henderson-Hasselbalch equation describes a relationship between which two factors?

Answer 27

local pH and degree of ionisation

Question 28

What does Henderson-Hasselbalch equation demonstrate?

Answer 28

Small changes in pH may significantly influence the ionisation of a drug (therefore rate of absorption and diffusion)

Question 29

To pass across a lipid layer, what must a drug be? (2)

Answer 29

- in solution | - lipid soluble (have high lipid solubility)

Question 30

What is the term which describes the ratio of the amount of drug which dissolves in the lipid and water phase when they are in contact?

Answer 30

Lipid-water partition coefficient

Question 31

What are main properties of passive diffusion in terms of: 1. conc. gradient 2. selectivity 3. saturation 4. carrier needed

Answer 31

1. moves along concentration gradient (no energy needed) 2. non-selective 3. not saturable 4. no carrier needed

Question 32

What are main properties of active transport in terms of: 1. conc. gradient 2. selectivity 3. saturation 4. carrier needed

Answer 32

1. moves against concentration gradient ( energy needed) 2. selective/ specific 3. saturable 4. carrier needed (reversible bound)

Question 33

What are main properties of facilitated diffusion in terms of: 1. conc. gradient 2. selectivity 3. saturation 4. carrier needed

Answer 33

1. moves along the concentration gradient (no energy needed) 2. selective/ specific 3. saturable 4. carriers needed

Question 34

What 2 forces drive filtration/ bulk flow/ pore transport?

Answer 34

- Hydrostatic force | - osmotic pressure difference across the membrane

Question 35

What 3 factors affect gastrointestinal absorption of drugs?

Answer 35

1. gut motility 2. food 3. illness (malabsorption)

Question 36

What is first pass metabolism?

Answer 36

metabolism of drug prior to reaching the systemic circulation ( affected by enzymes and acid in Gi tract and liver enzymes)

Question 37

Which drug administration method uses first pass metabolism?

Answer 37

Oral route

Question 38

what are the main consideration for mode of drug administration? (4)

Answer 38

- purpose and site of drug action - patient's ability to take medicine - speed of action needed - reliability of absorption

Question 39

What main 3 chemical properties determine absorption at different sites?

Answer 39

- pH - lipid solubility - ionisation

Question 40

Which administration methods avoid first pass metabolism? (7)

Answer 40

1. subcutaneous 2. intramuscular 3. GI administration (sublingual and rectal) 4. Inhalation 5. Nasal 6. Transdermal 7. intravenous

Question 41

Which administration methods provide instant absorption/ action? (4)

Answer 41

1. intravenous 2. intramuscular 3. subcutaneous 4. Other GI: sublingual

Question 42

Which administration methods might have slow absorption? (5)

Answer 42

1. oral 2. transdermal 3. inhalation 4. nasal 5. Other GI: rectal