PSA Cardiovascular Prescribing 3 — Questions and Answers
Question 1: A 75-year-old woman with non-valvular AF and a CHA₂DS₂-VASc score of 4 requires anticoagulation. Which agent is most appropriate as first-line therapy?
- Aspirin 75mg daily
- Clopidogrel 75mg daily
- Apixaban 5mg twice daily (Correct answer)
- Warfarin with target INR 2–3
Correct answer: Apixaban 5mg twice daily
DOACs such as apixaban are recommended over warfarin for non-valvular AF due to superior efficacy and safety; antiplatelet therapy is not an acceptable alternative.
Question 2: A 68-year-old man with AF and CKD (eGFR 25 mL/min) needs anticoagulation. Which DOAC is most problematic at this level of renal impairment?
- Rivaroxaban
- Apixaban
- Dabigatran (Correct answer)
- Edoxaban
Correct answer: Dabigatran
Dabigatran is approximately 80% renally eliminated and is contraindicated when eGFR < 30 mL/min, making it the most problematic DOAC in severe CKD.
Question 3: A patient on warfarin for AF presents with an INR of 8.5 and no active bleeding. What is the most appropriate initial management?
- Administer vitamin K 10mg IV immediately
- Withhold warfarin, give oral vitamin K 1–2.5mg, and recheck INR in 24 hours (Correct answer)
- Continue warfarin at the same dose and recheck INR in 48 hours
- Administer fresh frozen plasma immediately
Correct answer: Withhold warfarin, give oral vitamin K 1–2.5mg, and recheck INR in 24 hours
For markedly elevated INR (>8) without active bleeding, withholding warfarin and administering low-dose oral vitamin K 1–2.5mg is the appropriate management.
Question 4: A 78-year-old man on apixaban 5mg twice daily for AF has his medication reviewed. His weight is 58kg and serum creatinine is 140 µmol/L. What dose adjustment is required?
- No adjustment needed; continue 5mg twice daily
- Reduce to 2.5mg twice daily based on two criteria being met (Correct answer)
- Stop apixaban and switch to warfarin
- Increase to 10mg twice daily due to high stroke risk
Correct answer: Reduce to 2.5mg twice daily based on two criteria being met
Apixaban dose should be reduced to 2.5mg twice daily when at least 2 of 3 criteria are met: age ≥80, weight ≤60kg, or creatinine ≥133 µmol/L; this patient meets weight and creatinine criteria.
Question 5: A patient with AF on rivaroxaban 20mg daily requires an elective colonoscopy with low bleeding risk. When should rivaroxaban be withheld?
- 6 hours before the procedure
- 12 hours before the procedure
- 24 hours before the procedure (Correct answer)
- 48 hours before the procedure
Correct answer: 24 hours before the procedure
For procedures with low bleeding risk, rivaroxaban should be withheld for 24 hours (one dose missed) prior to the procedure given its half-life of 5–9 hours.
Question 6: An 80-year-old woman with AF on warfarin has had time in therapeutic range (TTR) of 38% over the past 6 months despite good adherence. What is the most appropriate next step?
- Increase the target INR range to 3–4
- Switch to low molecular weight heparin long-term
- Consider switching to a DOAC (Correct answer)
- Add aspirin 75mg to improve stroke prevention
Correct answer: Consider switching to a DOAC
Consistently poor TTR (<65–70%) on warfarin despite adherence is an indication to switch to a DOAC in eligible patients with non-valvular AF.
Question 7: A 66-year-old man with AF on apixaban 5mg twice daily is prescribed clarithromycin for a respiratory tract infection. What is the primary concern?
- Clarithromycin reduces apixaban levels, increasing stroke risk
- Clarithromycin inhibits CYP3A4 and P-glycoprotein, substantially increasing apixaban exposure and bleeding risk (Correct answer)
- The combination causes QT prolongation and torsades de pointes
- Clarithromycin induces CYP3A4, accelerating apixaban clearance
Correct answer: Clarithromycin inhibits CYP3A4 and P-glycoprotein, substantially increasing apixaban exposure and bleeding risk
Clarithromycin is a potent dual inhibitor of CYP3A4 and P-glycoprotein, both major elimination pathways for apixaban, leading to significantly elevated drug levels and bleeding risk.
PSA Cardiovascular Prescribing 3
A 75-year-old woman with non-valvular AF and a CHA₂DS₂-VASc score of 4 requires anticoagulation.
Which agent is most appropriate as first-line therapy?