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Principles of Disease > Drug metabolism > Flashcards

Drug metabolism Flashcards

1
Q

Define drug metabolism

A

A biochemical modification to pharmaceutical substances by living organisms, usually through activity of specialised enzymes.

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2
Q

4 main sites of drug metabolism?

A

Liver
Lungs
Gut linings
Kidneys

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3
Q

What is a prodrug?

A

A precursor to a drug which is converted to its active form by metabolism e.g. Codeine

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4
Q

What are the 3 outcomes of metabolism on a drug?

A
  • activation (prodrugs)
  • deactivation/ loss of activity
  • production of toxic metabolites
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5
Q

What does “wide substrate specificty” of metabolic enzymes mean?

A

Many drugs can be metabolism by more than one enzyme

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6
Q

What are the 3 types of phase 1 metabolism? (HOR)

A

Hydrolysis
or Oxidation
or Reduction

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7
Q

Whats the functions of phase 1 metabolism?

A

To increase polarity of the compound and to provide an active site for phase 2 to occur.

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8
Q

What family of enzymes carry out phase 1 metabolism?

A

P-450 family of enzymes

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9
Q

What is the prefix for the enzymes in phace 1 metabolism?

A

CYP is the prefix followed by no-letter-no

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10
Q

What are the 3 enzymes in phase 1 metabolism?

A

CYP3A4

CYP2D6

CYP1A2

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11
Q

Where is CYP3A4 found?

A

Liver

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12
Q

What does CYP2D6 metabolise?

A
  • antidepressants and antipyschotics

- convert codeine to morphine

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13
Q

How does smoking affect CYP2D6?

A

CYP2D6 is induced by smoking

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14
Q

What does CYP1A2 metabolise?

A

Theophylline

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15
Q

Which phase 1 enzyme isn’t induced by smoking?

A

CYP3A4 isn’t induced by smoking

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16
Q

What phase involves conjugation?

A

Phase 2 metabolism involves conjugation

17
Q

What is conjugation?

A

Combining drugs with other substances to terminate their activity

18
Q

How does conjugation make excretion of the drug easier?

A

Conjugated drugs have an increased water solubility

19
Q

What substances are used to conjugate the metabolites formed in phase 1?

A
  • Glucoronic acid
  • Glutathione
  • Sulphate
  • Acetate
20
Q

Does conjugation deactivate all drug metabolites?

A

Most but not all are inactivated

21
Q

In what two ways do other drugs/herbal meds affect drug metabolism?

A

-Enzyme induction
-Enzyme inhibition
, therefore affecting metabolic rates

22
Q

What is enzyme induction?

A

One substance causes an increased synthesis of the enzyme, leading to a greater metabolic rate

23
Q

What are some common inducers?

A

Other drugs, herbals, smoking and alcohol

24
Q

How long does it take for enzyme induction to become apparent?

A

Weeks -> months

25
Q

Is enzyme inhibition reversible?

A

Some enzyme inhibition is reversible but not all and some are irreversible

26
Q

What are some common substances that inhibit drug metabolising enzymes?

A
  • Erythromycin
  • Clarythromycin
  • Grapefruit
27
Q

What is pharmacogenetics?

A

The wide genetic variability in pharmacokinetics and pharmacodynamic response to drugs between individuals?

28
Q

What are the consequences of “bad” pharmacogenetics?

A
  • Therapeutic failure

- Adverse reactions

29
Q

How can genetic variation lead to drug toxicity?

A

Genetic variation

  • > absence/deficiency in an enzyme.
  • > overly high drug level
30
Q

How can genetic variation lead to therapeutic failure without adverse reactions?

A
  • over production of an enzyme
  • overly high metabolic activity
  • low drug conc. in blood
  • failure of therapy
31
Q

What two aspect of the liver can effect drug metabolism?

A
  • liver disease

- hepatic blood flow

32
Q

What are the two main differences in the drug metabolism of infants to adults?

A

infants have

  • reduced or absent drug metabolising enzymes
  • reduced renal function
33
Q

How is a pubescent Childs metabolism different to an adults?

A

By puberty, a Childs metabolism is faster than an adults.

34
Q

Which parameters affecting drug metabolism are affected in the elderly?

A

the elderly have

  • lower liver weight
  • lower renal function
  • lower plasma protein
  • lower lean body mass
35
Q

How does chronic disease in the elderly affect drug metabolism?

A

-Chronically ill elderly people are on multiple medication which can interact or simply overpower the body

36
Q

How does gender affect drug metabolism?

A

Affects all 4 areas of pharmacokinetics:

  • absorption
  • dsitrubtion
  • metabolism
  • excretion
37
Q

How does pregnancy affect drug metabolism?

A

Hormonal Changes in 2nd/3rd trimester induces some Drug metabolsing enzymes

38
Q

How does ethnicity affect drug metabolism

A

Variation in expression of P-450 genes leading to different levels of drug metabolising enzymes between races

39
Q

What is knowing ADME important for?

A
  • choosing method of administration
  • choosing safe and effective dosages/frequencies
  • making changes based of drugs, illnesses or physiological factrs

Principles of Disease (53 decks)

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