Toxicology

Question 1

What is the toxic by-product of paracetamol?
What is it reduced by?
What is it reduced to?

Answer 1

NAPQI
Reduced by glutathione to nontoxic mercaptate and cysteine compounds

Question 2

Which of the following opiod has increased risk of QT prolongation?
Oxycontin
Oxynorm
Methadone
Buprenorphine
Hydromorphone

Answer 2

Methadone

Question 3

What is the mechanism of action of Methylnaltrexone? Why is this good in palliative care?

Answer 3

MOA = peripherally acting mu-opioid receptor antagonist that specifically targets opioid receptors in the gut without crossing the blood-brain barrier
Pall care = does not interfere with morphine’s analgesic effect on the central nervous system.

Question 4

What is the conversion of codeine to morphine?

Answer 4

10:1

Question 5

Which is more likely to cause a dystonic reaction;
Domperidone or Metoclopramide?
Why?
Which one is best to use in Parkinson’s disease?

Answer 5

Dystonic = Metoclopramide
- Crosses through the blood brain barrier
Parkinsons = Domperidone

Question 6

Drug elimination kinetics:
Zero order?
First order?
Non-linear?
Examples

Answer 6

Zero order = set amount metabolised per time, straight line on graph
E.g. = Fluoxetine, Omeprazole
First order = a constant proportion (eg. a percentage) of drug is eliminated per unit time
E.g. = most drugs
Non-linear = drug at low concentration is cleared by first-order kinetics and at high concentrations by zero order kinetics
E.g. phenytoin or ethanol

Question 7

Which one of the following medications is most likely to cause foetal abnormalities if taken in the first trimester of pregnancy?

Warfarin.
Tetracycline
Enalapril.
Ibuprofen.
Heparin

Answer 7

Warfarin

Neither unfractionated heparin nor low-molecular-weight heparin crosses the placenta , and thus there is no possibility of teratogenesis or fetal hemorrhage with these drugs when used for the treatment of VTE.

Question 8

A 24-year-old woman is on doxycycline 100 mg/day for moderately severe acne. She wants to become pregnant. In terms of foetal outcome, at what stage of pregnancy (measured from last menstrual period) is the risk to the foetus greatest from exposure to doxycycline?

12-40 weeks
4-8 weeks
8-12 weeks.
0-4 weeks
Pre-conception.

Answer 8

12-40 weeks

Doxycycline should not be administered during pregnancy because of potential adverse effects to the fetus including dysplasia and inhibition of bone growth and dental discoloration.

Question 9

What are the features of neuroleptic malignant syndrome?
Are first or second generation anti-psychotics more likely to cause neuroleptic malignant syndrome?
Drug example?

Answer 9

Fever, hypertonia, hyporeflexia
First generation
Haloperidol