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MD3002 Pharmacology > Drug Metabolism and Elimination > Flashcards

Drug Metabolism and Elimination Flashcards

1
Q

What are the sites of metabolism in the body?

A
  • Gut lumen
  • Gut wall
  • Plasma
  • Lungs
  • Kidneys
  • Nerves
  • Liver
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2
Q

What can the result of metabolism be?

A
  • Pharmacological deactivaation
  • Pharmacological activation
  • Type of pharmacological response
  • No change in pharmacological activity
  • Change in drug uptake
  • Change in drug distribution
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3
Q

What does phase 1 metabolism usually involve?

A
  • Oxidation, reduction or hydrolysis- “functionalisation”

- Product often more reactive

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4
Q

WHat does phase 2 metabolism involve?

A
  • Synthetic conjugative reactions

- Hydrophilic, inactive compounds generated (usually)

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5
Q

Where does the majority of phase 1 metabolism occur?

A

The liver

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6
Q

What are 3 types of phase 1 oxidation reactions?

A
  • Mixed-function oxidase system (cytochrome P450)
  • Alcohol dehydrogenase
  • Xanthine oxidase
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7
Q

What are 3 types of phase 1 reduction reactions?

A
  • Ketone reduction

- Anaerobic cytochrome P450 metabolism

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8
Q

What are 3 types of phase 1 hydrolysis reactions?

A
  • Ester hydrolysis (e.g. cholinesterases)

- Amide hydrolysis

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9
Q

What enzymes are responsible for the majority of phase 1 metabolisms?

A

CYP450

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10
Q

Where are cytochrome P450s found?

A
  • Liver (mostly)
  • Kidney
  • Lung
  • Intestine
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11
Q

What does Cytochrome P450 require ?

A
  • NAPDH-CYP450 reductase
  • Lipid
  • Molecular oxygen
  • NADPH
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12
Q

Where can drugs be excreted after phase 2 metabolism?

A

bIle or urine (water-soluble)

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13
Q

What type of reaction turns aspirin to salicylic acid?

A

Hydrolysis

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14
Q

What happens to salicylic acid?

A
  • 13% excreted in urine
  • 4% oxidised (phase1)
  • 34% glucuronidation (phase 2), can be excreted in feces
  • 49% glycination (phase2)
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15
Q

What kind of drugs are eliminated more readily?

A

Hydrophilic over lipophilic

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16
Q

What organ is most responsible for the elimination of drugs and its metabolites?

A

Kidneys

17
Q

How are drugs transfered from plasma to bile?

A
  • Organic cation transporters (OCTs)
  • Organic anion transport (OATs)
  • P-glycoproteins (P-GP)
18
Q

What can hydrolysis of drug conjugate result in?

A

Reabsorption of the liberated drug via the enterohepatic circulation

19
Q

What transporters are thought to be responsible for multi-drug resistance (e.g chemotherapy)?

A
  • P-glycoproteins (P-GP)
20
Q

How can certain antibiotics interfere with certain drugs?

A

Gut microbiota facilitates the enterohepatic circulation has been destroyed (e.g oral contraceptives)

21
Q

What drugs will not be filtered by the glomerulus?

A
  • Drugs above 20 kDa in molecular weight

- Bound to plasma albumin

22
Q

What percentage of drug will diffuse across the renal tubule if it is freely permeable?

A

99%

23
Q

What happens to salicylate clearence as urinary pH increases?

A

Clearence increases (as it is a weak acid)

24
Q

What does zero order kinetics mean?

A

Constant rate or a constant proportion of drug removed per unit time

25
Q

What is 1st order kinetics?

A
  • Drug is being removed at a constant rate or a constant proportion per unit time (meaningful half-life)
  • More drug, faster metabolism
26
Q

What rule does salicylic acid follow in terms of kinetics?

A
  • Non-linear
  • High doses saturate
  • Follows first order but can follow zero order at high doses
27
Q

Clearence and Vd

A

LEARN again

28
Q

What is the half life equation?

A

(ln2 x Vd) / (CL)

29
Q

What is cleared more quickly aspirin or salicyclic acid?

A

Salicyclic acid (so lower clearence), higher half-life

30
Q

What is the most important pharmacokinetic parameter to consider?

A

Clearence

MD3002 Pharmacology (7 decks)

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