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Pharmacology > Drug Absorption into blood > Flashcards

Drug Absorption into blood Flashcards

1
Q

What 2 ways do drugs move around the body

A

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

2- diffusion: across barriers such as cellular membranes

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2
Q

Which type of drug can freely move across barriers

A

Unionised/lipid soluble (from high to low conc)

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3
Q

How do water soluble drugs cross barriers/membrane

A

Aqueous channels

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4
Q

How can drugs move across via carrier proteins

A

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

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5
Q

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

A

Percutaneous

Drug goes straight to plasma

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6
Q

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

A

Intravenous (into vein)

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7
Q

What route do oral or rectal administration take

A

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

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8
Q

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

A

Kidney and then excreted as urine or faeces

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9
Q

What is administration into muscle called

A

Intramuscular

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10
Q

What is intrathecal administration

A

Into cerebrospinal fluid

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11
Q

Is inhalation a way of administration?

A

Yes , Gas or powder

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12
Q

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

A

Into cell = influx

Out of cell = efflux

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13
Q

Which route is best for steady state absorption

A

Percutaneous/dermal (skin)

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14
Q

When are 4 times injections used

A

When drugs are poorly absorbed

Fast metabolism of drug in gut

For fast action

Dose control required

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15
Q

What is a single injection and constant injection called

A

Single = bolus

Constant = infusion

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16
Q

What are 3 types of injection

A

Intravenous (fast response)

Intramuscular (slow diffusion)

Subcutaneous (skin injection)

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17
Q

How are intramuscular injections taken

A

Through depot injection which is oil based for slow diffusion

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18
Q

With oral administration it goes to the gastrointestinal tract

Which part of the tract isn’t site of absorption

A

Stomach - ph is too acidic it would ionise drug

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19
Q

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

A

1- microvilli = increase SA

2- vascularised- good blood supply

3- enterocytes which contain transporters for drugs

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20
Q

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

A

Passive channels

Atp binding cassettes for efflux against conc gradient

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21
Q

What is bad about enterocytes

A

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

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22
Q

Where do drugs influx to from the enterocytes in small intestine

A

Into blood stream then to liver via portal system

23
Q

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

A

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

24
Q

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

A

Because it is site of metabolism like enterocytes are

Can affect drug absorption

25
Q

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

A

Bioavailable drugs

Go to the systemic circulation

26
Q

What is enterohepatic recirculation

A

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

27
Q

Name some first pass metabolised drugs

A

Aspirin , propanolol, lidocaine

28
Q

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

A

1- sublingual (spray under tongue into circulation)

2- rectal suppositories

29
Q

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

A

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

30
Q

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

A

Inhalation (powder or gas)

Cornea

Nasal (spray)

Vaginal

Transdermal (skin patch)

31
Q

Why is vaginal administration not always good for absorption

A

Ph can change for example in menstruation

Changes the ionisation of the drug

32
Q

Give an example of transdermal parentral administration

A

Stick on patches for hormone therapy

33
Q

What are 6 factors affecting drug absorption

A 
Size of drug 
Membrane permeability 
Skin hydration - better if hydrated
Pka of drug
Metabolism of drug 
Lipid solubility of drug (better if so)
34
Q

Why is ph affecting crossing of the membrane

A

Because if ionised then they can’t be lipid soluble

35
Q

When are acidic drugs ionised so can’t pass membrane

A

When in alkali conditions

36
Q

When are alkaline drugs ionised

A

When in acidic conditions

37
Q

What is it called exploiting ph of drug to cause excretion

A

Ion trapping

38
Q

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

A

They can pass through aqueous channels at the enterocytes

39
Q

What are the 4 classes of drug

A

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

40
Q

Why is class 2 excreted before entering GI tract

A

Because they can’t be solulised in the GI tract

41
Q

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

A

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

42
Q

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

A

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

43
Q

Why would too fast gastric motility cause lack of absorption

A

It would be excreted before being absorbed into the gut wall

44
Q

Why would taking drugs with food increase absorption/ rapid response

A

Because it will increase flow of digestive system

45
Q

What on drugs affect it’s ability to be absorbed

A

The capsule

46
Q

What is Cmax and Tmax

A

Cmax = max concentration of drug in plasma

Tmax = time of max conc in plasma

47
Q

How would you calculate total drug exposure

A

Split area under curve into trapeziums then do

average plasma conc x time interval of the area

Add all together

48
Q

How would you calculate bioavailability of the drug

A

(Exposure orally / exposure intravenous(100%))

X

(Dose of intravenous / dose of oral)

49
Q

What is Ka

A

Rate of absorption

50
Q

What does a lower Tmax mean for Ka

A

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

51
Q

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

A

Steady state

52
Q

What is C0

A

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

53
Q

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

A

Dose / Vd

Pharmacology (24 decks)

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