Drugs and the liver

Question 1

For the drug paracetamol, state its:

• Phases
• Type of step in the phases
• Brief description of the phases

Answer 1

Phases:

• Phase I
• Phase II

Type of step in the phases

• Phase I: oxidation
• Phase II: sulphation

Brief description:
Phase I:
* paracetamol is oxidised, i.e, an oxygen atom is added to it

Phase II:

• When paracetamol enters sulphation, it releases a toxic substance called NAPQI
• Another substance called glutathione offsets the effects of NAPQI
• In paracetamol overdose, there is an excess of NAPQI and the body cannot make enough glutathione
• So, to treat overdose, a precursor to to glutathione is given called N- acetylcysteine.

Question 2

For the drug codeine, state its:

• Phases
• Type of step in the phases
• Brief description of the phases

Answer 2

Phase:
* Phase I

Type of step in the phase:
* Oxidation

Brief description of the phase:
* An oxygen atom is added to codeine

Question 3

For the drug morphine, state its:

• Phases
• Type of step in the phases
• Brief description of the phases

Answer 3

Phase:
* Phase II

Type of step in the phase:
* Glucuronidation

Brief description of the phase:

• Morphine is the only drug that is converted into a more active form in phase II
• All other drugs are inactivated

Question 4

For the drug warfarin, state its:

• Phases
• Type of step in the phases
• Brief description of the phases

Answer 4

Phase
* Phase I

Type of step in the phase
* Reduction

Brief description of the phase
* Warfarin is reduced to a more inactive form

Question 5

For the drug prilocaine, state its:

• Phases
• Type of step in the phases
• Brief description of the phases

Answer 5

Phase:
* Phase I

Type of step in the phase:
* Hydrolysis

Brief description of the phase:

• Hydrolysis is NOT catalysed by the CP450 system
• Uses plasma cholinesterases
• Can be extra- hepatic
• Context sensitive half- life

Question 6

For the drug prednisone, state its:

• Phases
• Type of step in the phases
• Brief description of the phases

Answer 6

Phase
* Phase I

Type of step in the phase
* Reduction

Brief description of the phase

• Occurs only in anaerobic conditions
• Prednisone is reduced to a more active drug