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PoD topics > Drugs 3: Drug Metabolism > Flashcards

Drugs 3: Drug Metabolism Flashcards

1
Q

What is the definition of drug metabolism?

A

Biochemical modification og pharmaceutical substances by living organisms usually through specialised enzymatic activity

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2
Q

What form do compounds need to be in to be excreted?

A

Water soluble and polar (changed from lipid soluble to water soluble)

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3
Q

What happens to water soluble substances?

A

Undergo excretion

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4
Q

What happens to lipid soluble substances?

A

they are passively reabsorbed from renal or extra renal excretory sites back into blood

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5
Q

Where is the main site where metabolism occurs? What are other sites? (3)

A

Liver

Other sites include: gut, kidneys, lungs

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6
Q

What is the purpose of metabolism?

A
  1. increase water solubility (to aid excretion)

2. deactivate compounds (may take several steps)

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7
Q

What is the name of a group of drugs which are ACTIVATED following metabolism?

A

Prodrugs (deactivated before metabolism and activated after metabolism)

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8
Q

What are 2 examples of prodrugs?

A
  1. codeine

2. enalapril

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9
Q

What are the 4 main effects of metabolism?

A
  1. loss of pharmacological activity
  2. decrease i nactivity with metabolites that show some activity
  3. increase in activity, more active metabolites ( prodrug activation)
  4. production of toxic metabolites
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10
Q

What can toxic metabolites cause? (3)

A
  1. direct toxicity
  2. carcinogenesis
  3. teratogenesis ( in foetus and embryo)
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11
Q

what 3 reactions occur in phase 1 metabolism?

A
  1. reduction
  2. oxidation
  3. hydrolysis
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12
Q

What occurs in phase 1 metabolism?

A

Polar groups are exposed, increasing molecule polarity and provides active site for phase 2.

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13
Q

What is the main superfamily of enzymes involved in phase 1 metabolism?

A

Cytochrome p-450 enzymes (their different isoforms)

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14
Q

Is specificity relative or absolute?

A

Relative

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15
Q

What is the drug substrate for CYP1A2 enzyme and what does it treat?

A

theophylline: used for COPD and asthma patients

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16
Q

What is CYP1A2 production induced by?

A

smoking

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17
Q

What is the drug substrate for CYP2D and what does it treat?

A

Codeine: pain relief

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18
Q

What does CYP2D convert codeine to?

A

morphine

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19
Q

What additional group of drugs does CYP2D metabolise, other than codeine? (2)

A

Metabolism of antidepressants and antipsychotics

20
Q

What is the drug substrate for CYP3A4 and what does it treat?

A

Cyclosporine: immunosuppressant which is used in organ transplantations to decrease chances of organ rejection

21
Q

What other drugs does CYP3A4 metabolise, outside cyclosporine?

A

wide range of drugs; e.g. diazepam, methadone, simvastatin, CCBS

22
Q

What main event occurs in phase 2 metabolism and what does it do?

A

Conjugation; increases water solubility and enhances excretion of metabolised compound

23
Q

What substances attach to metabolites from phase 1 during phase 2?

A

glucuronic acid
glutathione
sulphate
acetate

24
Q

What does conjugation in phase 2 result in?

A

Inactivation

25
Q

What are some factors which often affect metabolism? (~9)

A
  1. other drugs/herbals/natural substances
  2. genetics
  3. hepatic blood flow
  4. liver disease
  5. age
  6. sex
  7. ethnicity
  8. pregnancy
  9. state of disease
26
Q

What are the most common enzyme inducers which induce metabolism?

A

Alcohol and smoking

27
Q

What other drugs and herbals can induce metabolising enzymes?

A
  • phenytoin
  • carbamazepine
  • rifampicin
  • St John’s Wort
28
Q

Is enzyme induction a fast or slow process?

A

Slow

29
Q

Which antibiotics commonly inhibit drug metabolising enzymes?

A
  • cimetidine
    -erythromycin
    -clarithromycin
    -ketoconazole
    ( and CCBs (Ca channel blocker), grapefruit)
30
Q

Is enzyme inhibition a fast or slow proces?

A

Fast

31
Q

Which enzyme does grapefruit juice cause a decrease in its production?

A

CYP3A (drugs have a narrower therapeutic range so altered enzyme means they cannot be metabolised)

32
Q

What is gene polymorphism in terms of enzymes?

A

Drug metabolising enzymes are often expressed in different forms, so inter-individual differences in gene expression are common

33
Q

What can mutations in metabolic enzymes results in? (2)

A
  1. enhanced enzyme activity (fast metaboliser)

2. inhibited enzyme activity (slow metaboliser)

34
Q

What can an abnormally fast metabolism lead to?

A

reduced drug effect as it will be metabolised too quickly or drug resistance

35
Q

What can an abnormally slow metabolism lead to?

A

increased drug toxicity

36
Q

What 3 enzymes commonly have polymorphisms?

A
  • CYP2D 5
  • CYP2C 9
  • CYP2C 19
37
Q

How many phenotype subpopulations of metabolisers does CYP2D 5 polymorphism have?

A

4:
- poor
- intermediate
- extensive
- ultrarapid

38
Q

How many nucleotide polymorphisms does CYP2D 5 have

A

70 nucleotide polymorphisms

39
Q

How many commonly used drugs are metabolised by CYP2D 5?

A

65 drugs

40
Q

How many commonly used drugs are metabolised by CYP2C 9 polymorphisms?

A

16 drugs

41
Q

what two drugs are the main 2 substrates for CYP2C 9?

A
  • warfarin

- phenytoin

42
Q

What are some examples of enzymes exhibiting genetic variation?

A
  1. pseudocholinesterase
  2. N-acetyltransferase
  3. cytochrome P450 2D6
  4. cytochrome P450 2C 19
  5. TMPT
43
Q

What enzyme isoforms are expressed in racial differences between populations?

A

P-450 isoforms

44
Q

Why is ADME important?

A
  • det. how to get drug to site of action
  • det. dose and frequency
  • predicting and avoiding toxicity
  • effective dose
  • making changes base don other drugs/illnesses
45
Q

By what age can children metabolise many more drugs much rapidly?

A

at 2 years old onward ( at puberty metabolism rate is greater than in adults)

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