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Principles of Disease HQ > Pharmacokinetics - ADME > Flashcards

Pharmacokinetics - ADME Flashcards

1
Q

What is the pharmacokinetic process?

A

Getting the drug to the site of action

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2
Q

What is the pharmacodynamic process?

A

Producing the correct pharmacological effect

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3
Q

What four events happen as part of the pharmacokinetic process?

A

Absorption
Distribution
Metabolism
Excretion

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4
Q

What is drug absorption?

A

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

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5
Q

What is Tmax?

A

time taken for a drug to reach peak concentration in the body

comes earlier if absorption if the drug is more rapid

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6
Q

What is Cmax?

A

peak concentration of the drug in the body

affected by increases in dosage

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7
Q

What is AUC?

A

the amount of the drug that reaches the systemic circulation

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8
Q

What is bioavailability?

A

the amount of a drug that reaches systemic circulation and is available for action

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9
Q

What is the therapeutic range of a drug?

A

the area where drug concentration if safe and active

above = toxicity
below = ineffective
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10
Q

What are the factors that effect the bioavailability of oral absorption if drugs?

A
  • formulation
  • physiological barriers
  • gastrointestinal effects
  • first pass metabolism
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11
Q

What type of drugs are absorbed through diffusion?

A

Non-ionised drugs (weak acids/bases, changes in pH change ability to diffuse)

Lipophilic drugs (must be lipid-soluble to diffuse through lipid membranes)

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12
Q

What must drugs resemble in order to be absorbed by active transport?

A

Naturally-occurring compounds

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13
Q

What is the main gastrointestinal factor that influences drug absorption?

A

Motility;

  • speed of gastric absorption
  • affected by food/drink/illnesses
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14
Q

What illnesses can affect GI motility?

A
  • Coeliac disease (gives rise to malabsorption)

- Migraine (reduces the rate of stomach emptying)

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15
Q

What is the first pass metabolism?

A

the metabolism of a drug before it can reach the systemic circulation

i.e. a drug could be fully metabolised before reaching the blood, e.g. insulin (reason for IV administration)

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16
Q

Why are other routes of drug absorption used?

A
  • absorption rate can be changed with different formulation
  • drugs with small volumes
  • blood flow differences
  • avoiding the first pass metabolism
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17
Q

Name four sites of drug administration, other than oral

A

Sublingual/Buccal
Rectal
Nasal
Transdermal

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18
Q

What is drug distribution?

A

the reversible transfer of a drug between blood and extravascular fluids/tissues in order for it to become active

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19
Q

What factors can influence drug distribution?

A 
Plasma protein binding
Tissue perfusion
Membrane characteristics
Transport mechanisms
Diseases
Other drugs
Elimination
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20
Q

What is plasma protein binding?

A

when drugs bind to plasma proteins such as albumin, nullifying their effects

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21
Q

What can affect the amount of a drug that is bound to plasma proteins?

A
  • renal failure
  • hypoalbuminaemia
  • pregnancy
  • other drugs (by displacement)
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22
Q

Name three parameters of the therapeutic range

A

Apparent volume of distribution (Vd)

Clearance (Cl)

Half-life (T1/2)

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23
Q

What is apparent volume of distribution?

A

theoretical volume needed to contain the total amount of a drug in the blood plasma if the drug was present in the same concentration throughout the body (L/Kg)

24
Q

What is caused by a greater Vd?

A

greater ability of a drug to diffuse to/through membranes

25
Q

What is clearance?

A

volume of fluid from which a drug is completely removed over a period of time (ml/min)

26
Q

What does renal clearance depend on?

A
  • concentration

- urine flow rate

27
Q

What does hepatic clearance depend on?

A
  • metabolism

- biliary excretion

28
Q

What is the half-life of a drug?

A

time taken for the drug concentration to decline by half its current value

29
Q

What does T1/2 depend on?

A
  • clearance

- apparent volume of distribution

30
Q

What is drug elimination?

A

removal of active drug/metabolites

31
Q

What processes can drug elimination be divided in to?

A

Metabolism (liver)

Excretion (kidneys/biliary system/gut)

32
Q

What four processes make up drug excretion?

A
  • glomerular filtration
  • active tubular secretion
  • passive tubular reabsorption
  • biliary secretion
33
Q

What sort of drugs are excreted by glomerular filtration?

A

unbound drugs, provided their size/shape/charge is relatively small

34
Q

Where does active tubular secretion occur?

A

in the proximal tubule

35
Q

What sort of drugs are excreted by active tubular secretion?

A
  • acidic/basic drugs

- protein bound cationic/anionic drugs

36
Q

Where does passive tubular reabsorption occur?

A

in the distal tubule and collecting duct

37
Q

What sort of drugs are excreted by passive tubular reabsorption?

A

unionised/highly concentrated drugs (diffusion across the concentration gradient)

38
Q

What occurs during biliary secretion?

A

drugs are passively/actively secreted into bile

39
Q

What is entero-hepatic circulation?

A

Drug reabsorption to circulation from bile

40
Q

What is drug metabolism?

A

biochemical modification of pharmaceutical substances by living organisms (usually by specialised enzymatic activity)

41
Q

How does drug metabolism work?

A

Lipophilic and non-polar substances are converted to hydrophilic and polar substances to allow them to undergo excretion instead of being passively reabsorbed

42
Q

What are prodrugs?

A

drugs with active metabolites which only become active after metabolism e.g. codeine (converted to morphine during metabolism)

43
Q

How can toxic drug metabolites affect the body?

A
  • direct toxicity
  • carcinogenesis
  • teratogenesis
44
Q

Describe pharmacokinetic enzymes in terms of specificity and presence in the body

A
  • have a wide substrate specificity

- constitutively expressed or induced by presence of substrate

45
Q

What processes occur during Phase 1 of drug metabolism?

A

Oxidation
Reduction
Hydrolysis

  • increases polarity
  • gives an active site for Phase 2 to occur
46
Q

What enzyme family is active during Phase 1 of drug metabolism?

A

Cytochrome P-450

47
Q

Name three subfamilies of the cytochrome P-450 enzyme active during Phase 1 of drug metabolism

A
  • CYP3A4
  • CYP2D6
  • CYP1A2
48
Q

What is the function of CYP3A4?

A
  • drug metabolism in the liver
  • pre-systemic metabolism in the gut
  • e.g. diazepam/methadone
49
Q

What is the function of CYP2D6?

A
  • antidepressant/antipsychotic metabolism
  • conversion of codeine to morphine
  • can be reduce/absent in some people (genetic polymorphisms)
50
Q

What is the function of CYP1A2?

A
  • induced by smoking
  • metabolism of theophylline
  • therefore smokers need a higher dosage of theophylline than non-smokers
51
Q

What processes occur during Phase 2 of drug metabolism?

A

Conjugation

  • attachment of substances to Phase 1 metabolites e.g. glucuronic acid/glutathione/sulphate/acetate
52
Q

What factors can affect drug metabolism?

A
  • other drugs
  • liver disease
  • hepatic blood flow
  • age
  • sex
  • ethnicity
  • pregnancy
  • genetics
53
Q

What can cause enzyme induction?

A
  • smoking
  • alcohol
  • St John’s Wort

(may take weeks)

54
Q

What can cause enzyme inhibition?

A
  • erythromycin
  • clarithromycin
  • grapefruit
55
Q

What are the four possible phenotypes of CYP2D6 polymorphism?

A
  • poor metabolizers (PM)
  • intermediate metabolizers (IM)
  • extensive metabolizers (EM)
  • ultrarapid metabolizers (UM)

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