MFDS Pharmacology 2 — Questions and Answers
Question 1: Which property of local anaesthetics determines their potency?
- Protein binding
- pKa
- Lipid solubility (Correct answer)
- Molecular weight
Correct answer: Lipid solubility
Lipid solubility determines the potency of local anaesthetics because a more lipophilic drug penetrates the lipid nerve membrane more readily.
Question 2: The onset of action of a local anaesthetic is primarily determined by its:
- Lipid solubility
- pKa (Correct answer)
- Protein binding
- Molecular weight
Correct answer: pKa
pKa determines onset: drugs with pKa closer to tissue pH (7.4) have a greater proportion in the uncharged (lipid-soluble) form that penetrates nerve membranes, giving faster onset.
Question 3: Adrenaline (epinephrine) is added to local anaesthetic solutions primarily to:
- Increase patient alertness
- Cause vasoconstriction and prolong anaesthesia (Correct answer)
- Alkalinise the solution
- Reduce systemic toxicity alone
Correct answer: Cause vasoconstriction and prolong anaesthesia
Adrenaline causes local vasoconstriction, reducing vascular uptake and thus prolonging the duration and depth of anaesthesia while reducing systemic absorption.
Question 4: Warfarin anticoagulation should be assessed before dental extractions using:
- APTT
- INR (Correct answer)
- Platelet count
- Bleeding time
Correct answer: INR
The INR (International Normalised Ratio) standardises measurement of the prothrombin time and is used to monitor warfarin therapy; dental extractions are generally safe below INR 4.0.
Question 5: Tetracyclines are contraindicated in children under 12 years because they:
- Cause nephrotoxicity
- Bind to calcium in developing teeth causing staining (Correct answer)
- Suppress bone marrow
- Cross the blood-brain barrier
Correct answer: Bind to calcium in developing teeth causing staining
Tetracyclines chelate calcium and are deposited in developing mineralised tissues, causing permanent yellow-brown staining and hypoplasia of teeth and bones.
Question 6: Which drug interaction is most clinically significant when prescribing metronidazole?
- Paracetamol
- Alcohol (disulfiram-like reaction) (Correct answer)
- Ibuprofen
- Amoxicillin
Correct answer: Alcohol (disulfiram-like reaction)
Metronidazole inhibits aldehyde dehydrogenase, causing accumulation of acetaldehyde when alcohol is consumed, producing a severe disulfiram-like reaction.
MFDS Pharmacology 2
Which property of local anaesthetics determines their potency?