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Pharmacology FoM > Pharmacokinetics- Metabolism > Flashcards

Pharmacokinetics- Metabolism Flashcards

1
Q

What is metabolism?

A

From the blood into metabolites

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2
Q

What is the purpose of metabolism?

A
  • To inactivate environmental toxins and make them more water-soluble so they can be excreted by the kidneys
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3
Q

What is conjugation?

A

Allows the metabolite to be excrete in the urine

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4
Q

What is the main organ of metabolism?

A
  • Liver

- Some metabolites are excreted in bile but most are returned to the general circulation

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5
Q

What is the clinical importance of metabolism of drugs?

A

Major source of inter-patient variability

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6
Q

What type of metabolism do oral drugs undergo?

A
  • Some first pass metabolism in liver before reaching systemic circulation
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7
Q

What type of metabolism do all drugs undergo?

A
  • Pass repeatedly through the liver

- A fraction may be metabolised on each pass (2nd/3rd pass metabolism)

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8
Q

Describe hepatic metabolism

A
  • Phase 1: oxidation, reduction, hydrolysis (inactivation)

- Phase 2: conjugation with glucuronide to make more water soluble (solubilisation)

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9
Q

What is cytochrome P450?

A
  • Family of membrane bound enzymes with different substrate specificities
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10
Q

What are haemoproteins?

A

Contain Fe, bind drug + oxygen or carbon dioxide

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11
Q

What do cytochrome P450s do?

A
  • Catalyse drug oxidation, reduction, hydrolysis in Phase 1

- Cooperate with other enzymes for conjugation in Phase 2

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12
Q

What are the main subfamilies for Cytochrome P450s?

A
  • CYP1A
  • CYP2A, CYP2C, CYP2D, CYP2E
  • CYP3A
  • Drug interactions may occur between 2 substrates for same CYP isozyme
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13
Q

What is the site of phase 1 metabolism in hepatocytes?

A

Cytochrome P450 isozymes mainly in SER of hepatocytes

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14
Q

What is the site of phase 2 metabolism in hepatocytes?

A

Performed by secondary enzymes, in cytoplasm

- Only lipid soluble drugs can dissolve and reach active site of CP450 embedded in lipid bilayer

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15
Q

What are the phase 2 conjugation reactions?

A
  • Glucurodination
  • Sulphation
  • Acetylation
  • Methylation
  • Amino-acid
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16
Q

What are the consequences of metabolism?

A
  • Converts most drugs to less active metabolites, but generates active metabolites from some drugs
  • May convert inactive drug to active drug
  • May generate toxic metabolites
  • May be affects by pharmacogenetics differences
17
Q

What does pharmacogenetics involve?

A
  • Metoprolol and CYP2D6
  • Alcohol flush- redness
  • Ethanol to acetaldehyde to acetate
  • Pharmacogenetics differences may require dosage adjustment or substitution

Pharmacology FoM (12 decks)

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