MJDF Pharmacology & Pain Control

Question 1

What is the mechanism of action of lidocaine as a local anaesthetic?

Accepted Answer

Blocks voltage-gated sodium channels, preventing action potential propagation in nerve fibres

Answer

Lidocaine blocks voltage-gated Na⁺ channels in the non-ionised form, preventing membrane depolarisation and propagation of action potentials along sensory and motor nerve fibres.

Question 2

Why does local anaesthesia work less effectively in infected tissue?

Accepted Answer

Acidic pH in infected tissue increases ionisation of LA, reducing membrane penetration

Answer

Infected tissue has a low pH; LA molecules (weak bases) are mostly in the ionised form at low pH, unable to cross the lipid nerve membrane, reducing effectiveness.

Question 3

What is the maximum safe dose of articaine with adrenaline for a 70 kg adult?

Accepted Answer

7 mg/kg (approximately 490 mg — about 5–6 cartridges of 4% articaine)

Answer

Articaine with adrenaline has a maximum dose of 7 mg/kg; at 70 kg, this is approximately 490 mg — equivalent to approximately 5–6 cartridges of 4% articaine (40 mg/ml, 1.7 ml per cartridge).

Question 4

What is the pharmacological reason for adding adrenaline to a local anaesthetic?

Accepted Answer

Causes local vasoconstriction, reducing systemic absorption, prolonging duration, and improving depth of anaesthesia

Answer

Adrenaline causes local vasoconstriction at the injection site, slowing systemic absorption, increasing LA concentration at the nerve, prolonging duration by 50–100%, and reducing systemic toxicity risk.

Question 5

Which group of patients requires special caution when administering adrenaline-containing local anaesthetic?

Accepted Answer

Patients taking non-selective beta-blockers (risk of hypertensive crisis)

Answer

Non-selective beta-blockers (e.g., propranolol) block β₂-mediated vasodilation, leaving α₁ vasoconstriction unopposed when adrenaline is given, potentially causing a hypertensive crisis with reflex bradycardia.

MJDF Part 1 Practice Test

MJDF Part 1 Practice Test

MJDF Pharmacology & Pain Control