FACEM Pharmacology Fundamentals 4

Question 1

A patient on warfarin develops bleeding after starting fluconazole. The most likely mechanism is:

Accepted Answer

Fluconazole inhibits CYP2C9, reducing warfarin metabolism

Answer

Fluconazole is a potent CYP2C9 inhibitor; since S-warfarin (the active enantiomer) is metabolized by CYP2C9, fluconazole raises warfarin levels and anticoagulant effect.

Question 2

Which statement about zero-order kinetics is correct in the context of emergency pharmacology?

Accepted Answer

Elimination rate is independent of drug concentration

Answer

In zero-order kinetics, elimination is saturable and proceeds at a constant rate (fixed amount per time) regardless of concentration, as seen with ethanol and phenytoin at toxic levels.

Question 3

The antidote for benzodiazepine overdose, flumazenil, acts by:

Accepted Answer

Competitively antagonizing benzodiazepines at the GABA-A receptor

Answer

Flumazenil competitively antagonizes benzodiazepines at the benzodiazepine-binding site on the GABA-A receptor complex, reversing sedation.

Question 4

Phenytoin exhibits dose-dependent (Michaelis-Menten) kinetics at therapeutic concentrations. The clinical implication is that:

Accepted Answer

Small dose increases can cause disproportionately large plasma level increases

Answer

Because phenytoin saturates its hepatic metabolic enzymes at therapeutic doses, small dose increments can produce large, unpredictable rises in plasma concentration.

Question 5

Which of the following correctly describes the mechanism of action of adenosine in terminating supraventricular tachycardia?

Accepted Answer

Activates A1 adenosine receptors, increasing K+ conductance and slowing AV conduction

Answer

Adenosine activates A1 receptors in the AV node, opening GIRK (IKAch) potassium channels, hyperpolarizing cells and transiently blocking AV conduction.

(FACEM) Fellowship of the Australasian College for Emergency Medicine Practice Test

(FACEM) Fellowship of the Australasian College for Emergency Medicine Practice Test

FACEM Pharmacology Fundamentals 4