APC APC Drug Interactions and Contraindications 2

Question 1

Which combination poses the greatest risk of clinically significant QT prolongation?

Accepted Answer

Azithromycin and haloperidol

Answer

Both azithromycin and haloperidol independently prolong the cardiac QT interval, and their combination greatly increases the risk of torsades de pointes.

Question 2

Lithium toxicity risk is significantly increased when a patient is also prescribed which drug?

Accepted Answer

Hydrochlorothiazide

Answer

Thiazide diuretics reduce renal sodium excretion, causing compensatory lithium reabsorption in the proximal tubule and elevated lithium plasma concentrations.

Question 3

Which drug interaction requires the pharmacist to counsel the patient to avoid grapefruit juice?

Accepted Answer

Atorvastatin therapy

Answer

Grapefruit juice inhibits intestinal CYP3A4, increasing atorvastatin bioavailability and raising the risk of myopathy and rhabdomyolysis.

Question 4

A patient on warfarin starts a course of broad-spectrum antibiotics. The pharmacist should counsel them to watch for signs of:

Accepted Answer

Enhanced anticoagulation and increased bleeding risk

Answer

Broad-spectrum antibiotics reduce gut flora that produce vitamin K, leading to decreased vitamin K levels and enhanced warfarin anticoagulation effect.

Question 5

Clopidogrel's antiplatelet efficacy is significantly reduced when combined with which drug class?

Accepted Answer

Proton pump inhibitors (PPIs)

Answer

Many PPIs, especially omeprazole, inhibit CYP2C19 which is required to convert clopidogrel to its active metabolite, reducing its antiplatelet effect.

(APC) Australian Pharmacy Council Practice Test

(APC) Australian Pharmacy Council Practice Test

APC APC Drug Interactions and Contraindications 2