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Mechanisms of Drug Action > ADME > Flashcards

ADME Flashcards

1
Q

What are the 2 main types of drug administration?

A
  • Enteral
  • Parental
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2
Q

Define enteral

A

via GI tract

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3
Q

Define parenteral

A

Not via GI tract

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4
Q

What is the main disadvantage of sublingual administration?

A

Drug must be lipid soluble (only suitable for small molecules)

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5
Q

Give 3 examples of enteral administration

A
  • oral
  • Sublingual
  • Rectal
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6
Q

What is the main advantage of rectal and sublingual administration?

A

Little 1st Pass effect

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7
Q

What are the advantages of intramuscular administration?

A

The drug sits in the muscle for a long time and is released slowly (ensures more vulnerable patients take the drug)

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8
Q

Give 3 examples of parenteral administration

A
  • Intravenous
  • Intramusclar
  • Subcutaneous
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9
Q

What is the oral bioavaliability of a drug?

A

Fraction of an oral dose that ends up in the systemic circulation

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10
Q

How is oral bioavaliability measured?

A
  • The same dose of a drug is administered 2 different ways and a Cp time graph is generated
  • Alternatively F can be found for 2 or more drugs given orally at different times provided the dose is the same
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11
Q

Why is isolated tissue used in oral bioavaliability studies?

A

It allows the drug to be easily washed off and addition of another drug made

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12
Q

Does bioavaliability affect the EC50 of a drug?

A

Yes

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13
Q

What factors affect the oral bioavaliability of a drug?

A
  • Poor absorption from the gut
  • Breakdown of drug in gut
  • First Pass effect
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14
Q

What is the 1st pass effect?

A
  • When drugs enter the bloodstream they first pass through the liver before entering the systemic circulation
  • The Liver contains many enzymes and so some drugs are heavily metabolised in the liver
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15
Q

What factors affect drug absorption at a membrane?

A
  • Lipid solubility
  • Ability to cross via passive diffusion
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16
Q

What factors affect absorbance of a drug?

A
  • pKa of drug and pH of absorbing surface
  • drug preparation
  • area of absorbing surface
  • rate of blood flow to absorbing surface ([gradient])
  • Food in stomach
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17
Q

Why can only the unionized form of a drug cross mucosal membranes?

A

Otherwise they are not lipid soluble enough

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18
Q

What is drug distribution?

A

Penetration of the drug into tissues and organs from the blood

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19
Q

What does the extent of distribution depend on?

A
  • Lipid solubility
  • Tightness/extent of plasma protein binding
  • Rate of blood flow to tissues
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20
Q

What is the usual affect of high lipid solubility on distribution?

A

Tends to increase extent of distribution

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21
Q

What is apparent volume of distribution?

A

Volume of water in which drug would have to be distributed to give its plasma concentration

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22
Q

What are the units of apparent volume of distribution?

A

Volume or volume/mass

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23
Q

Can apparent volume of distribution be larger than total body water?

A

Yes

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24
Q

What is useful about calculating volume distribution?

A
  • Partly determines plasma half life in blood
  • Used in pharmacokinetics calculations to design dosing schedules
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25
Q

Does apparent volume of distribution change?

A

Not usually

26
Q

Why might apparent volume distribution change?

A
  • Age (due to decreased intracellular water and increased fat)
  • Obesity (lipid soluble drugs)
27
Q

What is elimination?

A

Overall removal of drug from the body

28
Q

Where does metabolism occur in the body?

A
  • Liver (most important)
  • Lungs
  • Kidneys
  • Plasma
29
Q

What is half life of a drug?

A

The time taken for the plasma concentration of a drug to fall to half its initial value

30
Q

What is clearance?

A

The amount of plasma which is cleared of its drug content in unit time

31
Q

What are the features of 1st order drug elimination?

A
  • half life is constant
  • most common kinetics
  • rate of elimination depends on how much drug is present
32
Q

What are the features of 0 order drug elimination?

A
  • half life increases
  • saturation of elimination process
  • rate of process is independent of [drug]
33
Q

What is a pseudo 0 order elimination?

A

At [high] elimination process is saturated and so appears 0 order but as time increases the elimination becomes 1st order

34
Q

What is the Css?

A

The steady state concentration where rate of elimination=rate of infusion

35
Q

Approximately how many half lives are required for the Css to be reached (for 1st order kinetics)?

A

5

36
Q

How does infusion rate affect the Css?

A

The actual value of Css depends on the infusion rate but the time to reach it will not vary

37
Q

Generally how are drugs and metabolites which are not lipid soluble excreted?

A

Via the kidneys

38
Q

How can urinary excretion of a weak acid be increased?

A

Make the urine more alkaline

39
Q

How can urinary excretion of a weak base be increased?

A

Make urine more acidic

40
Q

Why is a prodrug sometimes used?

A

If the drug has low bioavaliability so otherwise would not get to the site

41
Q

What are the 3 types of metabolites drugs can form?

A
  • inactive
  • active
  • toxic
42
Q

Give an example of a drug which is metabolised to produce an active metabolite

A

Codeine (metabolised to morphine)

43
Q

What occurs in phase 1 of hepatic drug metabolism?

A

A drug derivative formed by introducing a reactive site into or exposing a reactive site on the drug molecule

44
Q

Why do phase 1 metabolism reactions make the drug derivative more reactive?

A

So it is more likely to undergo phase 2 reactions

45
Q

What occurs in phase 2 metabolic reactions?

A

The joining together of species formed in phase 1 with polar molecules making metabolites less lipid soluble and so easier to excrete in urine

46
Q

Is phase 2 catabolic or anabolic?

A

Anabolic

47
Q

Is phase 1 anabolic or catabolic?

A

Catabolic

48
Q

Do drugs have to undergo phase 1 metabolism?

A

No

49
Q

Where do phase 1 reactions usually occur?

A

On the endoplasmic reticulum of liver cells

50
Q

Where do phase 2 reactions usually occur?

A

In the cytosol of liver cells

51
Q

What is enzyme induction?

A

The process by which over some time some drugs can induce increased expression of cytochrome p450 enzymes

52
Q

What is the problem with enzyme induction?

A

Can cause the failure of some drugs to produce a clinical effect

53
Q

What factors affect drug metabolism?

A
  • Enzyme induction
  • Enzyme inhibition
  • Genetic polymorphism
  • Disease
  • Age
54
Q

What is the effect of enzyme induction on clearance?

A

It is increases clearance

55
Q

What is the effect of enzyme induction on Css?

A

Decreases it

56
Q

What is enzyme inhibition?

A

The process by which some drugs directly inhibit P450 enzymes, this occurs immediately after the drug is taken (no delay like induction)

57
Q

What is problem with enzyme inhibition?

A

It takes much longer for a drug to be broken down so can cause toxicity

58
Q

Disease of which organs affects drug metabolism most?

A
  • Liver
  • Kidneys
  • Thyroid (affects metabolising enzymes)
  • Heart (affects rate of delivery of drug to liver/kidney)
59
Q

How does age affect drug metabolism?

A

Generally the rate of drug metabolism is lower in the very young and old

60
Q

What affects the rate of elimination of a drug which is eliminated by a process of 1st order kinetics?

A

The concentration of drug

Mechanisms of Drug Action (8 decks)

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