Drug Absorption into blood

Question 1

What 2 ways do drugs move around the body

Answer 1

1- bulk flow: move in blood often bound to proteins like albumin

2- diffusion: across barriers such as cellular membranes

Question 2

Which type of drug can freely move across barriers

Answer 2

Unionised/lipid soluble (from high to low conc)

Question 3

How do water soluble drugs cross barriers/membrane

Answer 3

Aqueous channels

Question 4

How can drugs move across via carrier proteins

Answer 4

Either passively down electrochemical gradient OR using ATP binding cassettes from low to high conc

Question 5

What is drug administration into the skin called and where does it go

Answer 5

Percutaneous

Drug goes straight to plasma

Question 6

Which way of administration causes 100% of the drug to enter the plasma

Answer 6

Intravenous (into vein)

Question 7

What route do oral or rectal administration take

Answer 7

To the gut where they can enter blood or liver via portal vein

Question 8

Where does drug go after the gut if not to the plasma to be excreted

Answer 8

Kidney and then excreted as urine or faeces

Question 9

What is administration into muscle called

Answer 9

Intramuscular

Question 10

What is intrathecal administration

Answer 10

Into cerebrospinal fluid

Question 11

Is inhalation a way of administration?

Answer 11

Yes , Gas or powder

Question 12

What is the word given to drug moving into cell and out of cell

Answer 12

Into cell = influx

Out of cell = efflux

Question 13

Which route is best for steady state absorption

Answer 13

Percutaneous/dermal (skin)

Question 14

When are 4 times injections used

Answer 14

When drugs are poorly absorbed

Fast metabolism of drug in gut

For fast action

Dose control required

Question 15

What is a single injection and constant injection called

Answer 15

Single = bolus

Constant = infusion

Question 16

What are 3 types of injection

Answer 16

Intravenous (fast response)

Intramuscular (slow diffusion)

Subcutaneous (skin injection)

Question 17

How are intramuscular injections taken

Answer 17

Through depot injection which is oil based for slow diffusion

Question 18

With oral administration it goes to the gastrointestinal tract

Which part of the tract isn’t site of absorption

Answer 18

Stomach - ph is too acidic it would ionise drug

Question 19

What are 3 adaptations of the small intestine good for absorption by oral intake

Answer 19

1- microvilli = increase SA

2- vascularised- good blood supply

3- enterocytes which contain transporters for drugs

Question 20

Which carriers do enterocytes have to the gut lumen or to the blood

Answer 20

Passive channels

Atp binding cassettes for efflux against conc gradient

Question 21

What is bad about enterocytes

Answer 21

They contain metabolic enzymes which can degrade drug before it’s passed into the blood

Question 22

Where do drugs influx to from the enterocytes in small intestine

Answer 22

Into blood stream then to liver via portal system

Question 23

Why do drugs sometimes efflux out of gut wall into the gut lumen again

Answer 23

To stop body from harmful substances by the drug so it can be excreted to the kidney

Question 24

why is the liver a bad place for drugs to go from the gut wall

Answer 24

Because it is site of metabolism like enterocytes are

Can affect drug absorption

Question 25

What is the drugs called which don’t get metabolised by the liver by first pass metabolism and where do they go

Answer 25

Bioavailable drugs Go to the systemic circulation

Question 26

What is enterohepatic recirculation

Answer 26

Where drugs from the liver to back to the gut and to the gut wall to restart the cycle

Question 27

Name some first pass metabolised drugs

Answer 27

Aspirin , propanolol, lidocaine

Question 28

What are 2 gastrointestinal routes other than oral which stop first pass metabolism

Answer 28

1- sublingual (spray under tongue into circulation) 2- rectal suppositories

Question 29

Why does rectal administration only stop 2/3 of first pass metabolism

Answer 29

The superior vein in the rectum goes to the portal vein and then to the liver for first pass metabolism

Question 30

What are 5 ways of administration which aren’t gastrointestinal (don’t get metabolised first pass) = PARENTRAL

Answer 30

Inhalation (powder or gas) Cornea Nasal (spray) Vaginal Transdermal (skin patch)

Question 31

Why is vaginal administration not always good for absorption

Answer 31

Ph can change for example in menstruation Changes the ionisation of the drug

Question 32

Give an example of transdermal parentral administration

Answer 32

Stick on patches for hormone therapy

Question 33

What are 6 factors affecting drug absorption

Answer 33

``` Size of drug Membrane permeability Skin hydration - better if hydrated Pka of drug Metabolism of drug Lipid solubility of drug (better if so) ```

Question 34

Why is ph affecting crossing of the membrane

Answer 34

Because if ionised then they can’t be lipid soluble

Question 35

When are acidic drugs ionised so can’t pass membrane

Answer 35

When in alkali conditions

Question 36

When are alkaline drugs ionised

Answer 36

When in acidic conditions

Question 37

What is it called exploiting ph of drug to cause excretion

Answer 37

Ion trapping

Question 38

Why does solubility of drug in water cause increased levels of absorption in GI tract

Answer 38

They can pass through aqueous channels at the enterocytes

Question 39

What are the 4 classes of drug

Answer 39

Class 1- high water solubility and high permeability (unionised) Class 2- low water solubility but high permeability (unionised) Class 3- high water solubility but low membrane permeability Class 4- low solubility and permeability

Question 40

Why is class 2 excreted before entering GI tract

Answer 40

Because they can’t be solulised in the GI tract

Question 41

Why is class 3 high in conc at the GI tract but low absorption

Answer 41

Because it has high solubility increasing its conc in Gi tract but can’t pass the membrane due to being ionised

Question 42

How does gastric motility affect absorption if a drug is taken orally

Answer 42

If they have slow gastric motility the affect of the drug will also be slow

Question 43

Why would too fast gastric motility cause lack of absorption

Answer 43

It would be excreted before being absorbed into the gut wall

Question 44

Why would taking drugs with food increase absorption/ rapid response

Answer 44

Because it will increase flow of digestive system

Question 45

What on drugs affect it’s ability to be absorbed

Answer 45

The capsule

Question 46

What is Cmax and Tmax

Answer 46

Cmax = max concentration of drug in plasma Tmax = time of max conc in plasma

Question 47

How would you calculate total drug exposure

Answer 47

Split area under curve into trapeziums then do average plasma conc x time interval of the area Add all together

Question 48

How would you calculate bioavailability of the drug

Answer 48

(Exposure orally / exposure intravenous(100%)) X (Dose of intravenous / dose of oral)

Question 49

What is Ka

Answer 49

Rate of absorption

Question 50

What does a lower Tmax mean for Ka

Answer 50

Lower Tmax(time of max conc) = higher Ka (rate of absorption)

Question 51

What are you trying to achieve when taking repeated doses orally compared to fast IV

Answer 51

Steady state

Question 52

What is C0

Answer 52

Concentration in circulation at time O due to immediate distribution (one compartment model)

Question 53

How do you work out C0 (conc at time 0)

Answer 53

Dose / Vd