DOAC dose reduction, and the patients who still need warfarin

Study cases written by our editors, not BPS items. The real BCPS exam is computer-based multiple choice, answered in order with no going back.

1. Case 01

   An 82-year-old woman (57 kg) with nonvalvular atrial fibrillation, hypertension and diabetes (CHA₂DS₂-VASc 5) had an upper GI bleed while on warfarin 3 weeks ago; the bleeding ulcer was treated endoscopically and she now takes pantoprazole. SCr is 1.2 mg/dL (CrCl 32 mL/min). The team decides to resume anticoagulation. Which regimen is most appropriate?

   1. AOption A: Rivaroxaban 20 mg daily with the evening meal
   2. BOption B: Dabigatran 150 mg twice daily
   3. COption C: Apixaban 2.5 mg twice daily
   4. DOption D: Apixaban 5 mg twice daily

   Pick an option: the verdict and a note on every option open here.

   Best answer: C.

   Apixaban carries the lowest GI-bleeding risk among DOACs, and she meets two dose-reduction criteria (age 80 years or older and weight 60 kg or less), so 2.5 mg twice daily is correct even though her SCr is below 1.5 mg/dL. Apixaban 5 mg twice daily ignores those criteria. Rivaroxaban 20 mg is the dose for CrCl above 50 mL/min (15 mg is required at CrCl 15–50), and dabigatran 150 mg twice daily carries a higher GI-bleeding risk than warfarin and is also used with caution in older adults (Beers 2023).

   A

   Rivaroxaban 20 mg is for CrCl above 50 mL/min, and rivaroxaban carries more GI bleeding than apixaban in a patient who just bled.

   B

   Dabigatran 150 mg twice daily causes more GI bleeding than warfarin and is used with caution in older adults.

   C

   Correct. She meets two apixaban reduction criteria (age 80 or older, weight 60 kg or less), and apixaban has the lowest GI-bleed risk.

   D

   Full-dose apixaban ignores her age and weight, which together trigger the 2.5 mg dose even with an SCr below 1.5.

2. Case 02

   A 60-year-old man (84 kg) with nonvalvular atrial fibrillation had a minor ischemic stroke while taking warfarin; his INR has been labile (time in therapeutic range 45%). He has no mechanical valve or mitral stenosis. SCr is 1.0 mg/dL (CrCl 92 mL/min). The team decides to change his anticoagulation. Which regimen is most appropriate?

   1. AOption A: Apixaban 5 mg twice daily
   2. BOption B: Rivaroxaban 15 mg daily
   3. COption C: Warfarin with a target INR of 3.0–3.5
   4. DOption D: Dabigatran 75 mg twice daily

   Pick an option: the verdict and a note on every option open here.

   Best answer: A.

   DOACs are preferred over warfarin in nonvalvular AF (2023 ACC/AHA), especially with poor INR control, and apixaban at full dose is right because he meets no dose-reduction criteria. Raising the INR target to 3.0–3.5 is tempting after a stroke on warfarin, but it increases bleeding without proven benefit. Dabigatran 75 mg twice daily is the US dose for CrCl 15–30 mL/min and rivaroxaban 15 mg is the CrCl 15–50 mL/min dose, so both would underdose him.

   A

   Correct. A DOAC beats labile warfarin in nonvalvular AF, and with CrCl 92 and no reduction criteria apixaban is given at full dose.

   B

   Rivaroxaban 15 mg is the CrCl 15–50 mL/min dose; at CrCl 92 he would be underdosed.

   C

   A higher INR target after a stroke on warfarin adds bleeding risk without proven benefit, and his TTR is the real problem.

   D

   Dabigatran 75 mg twice daily is the US dose for CrCl 15–30 mL/min and underdoses him.

3. Case 03

   A 66-year-old woman (70 kg) with a mechanical bileaflet mitral valve placed 4 years ago now has atrial fibrillation (CHA₂DS₂-VASc 3). She has taken warfarin since surgery, but her INR has been hard to keep in range. She asks to switch to a DOAC because she has heard they are safer. SCr is 0.9 mg/dL. Which anticoagulant is most appropriate?

   1. AOption A: Apixaban 5 mg twice daily
   2. BOption B: Apixaban 2.5 mg twice daily
   3. COption C: Dabigatran 150 mg twice daily
   4. DOption D: Warfarin with INR monitoring

   Pick an option: the verdict and a note on every option open here.

   Best answer: D.

   The 2023 ACC/AHA/ACCP/HRS atrial fibrillation guideline prefers DOACs over warfarin for most patients with AF. The exceptions are patients with a mechanical heart valve or moderate-to-severe rheumatic mitral stenosis, who were excluded from the DOAC trials. For them, warfarin is recommended and DOACs are not. Dabigatran caused more thromboembolic and bleeding events than warfarin in patients with mechanical valves (RE-ALIGN), and its label lists mechanical prosthetic valves as a contraindication. An unstable INR is a reason to tighten INR monitoring and education, not to switch to a DOAC.

   A

   DOACs were not studied in mechanical valves and are not recommended there; apixaban fared worse than warfarin in a mechanical-valve trial.

   B

   The dose is not the issue: no DOAC dose is appropriate with a mechanical valve, and she meets no apixaban dose-reduction criteria.

   C

   Dabigatran increased both thrombosis and bleeding versus warfarin in mechanical valves and is contraindicated there by its label.

   D

   Correct. With a mechanical heart valve, warfarin remains the anticoagulant; a labile INR calls for closer INR management, not a DOAC.

4. Case 04

   A 79-year-old man (72 kg) with nonvalvular atrial fibrillation (CHA₂DS₂-VASc 4) is starting anticoagulation. SCr is 2.0 mg/dL (CrCl 29 mL/min) and has been stable for 6 months. He has no bleeding history and takes no interacting drugs. Which regimen is most appropriate?

   1. AOption A: Apixaban 5 mg twice daily
   2. BOption B: Dabigatran 150 mg twice daily
   3. COption C: Apixaban 2.5 mg twice daily
   4. DOption D: Edoxaban 60 mg daily

   Pick an option: the verdict and a note on every option open here.

   Best answer: A.

   Apixaban is reduced to 2.5 mg twice daily only when at least two of these are present: age 80 or older, weight 60 kg or less, SCr 1.5 mg/dL or higher; he meets only the SCr criterion, so 5 mg twice daily is correct. Apixaban 2.5 mg is the common underdosing error, which raises stroke risk. Dabigatran 150 mg is too high at CrCl 29 mL/min (75 mg twice daily in the US at CrCl 15–30), and edoxaban must be reduced to 30 mg daily at CrCl 15–50 mL/min.

   A

   Correct. Only one apixaban reduction criterion is present (SCr 2.0); age 79 and 72 kg do not count, so 5 mg twice daily stands.

   B

   At CrCl 29 mL/min the US dabigatran dose drops to 75 mg twice daily; 150 mg would accumulate.

   C

   Cutting to 2.5 mg with only one criterion is the classic apixaban underdosing error, which raises stroke risk.

   D

   Edoxaban must be reduced to 30 mg daily at CrCl 15–50 mL/min.

5. Case 05

   An 82-year-old man (weight 70 kg) with nonvalvular atrial fibrillation and stage 3b CKD will start rivaroxaban. His serum creatinine is 1.6 mg/dL. Using the Cockcroft-Gault equation with actual body weight, which regimen is most appropriate?

   1. AOption A: Rivaroxaban 10 mg once daily with or without food
   2. BOption B: Rivaroxaban 15 mg once daily with the evening meal
   3. COption C: Rivaroxaban 15 mg twice daily with food for 21 days
   4. DOption D: Rivaroxaban 20 mg once daily with the evening meal

   Pick an option: the verdict and a note on every option open here.

   Best answer: B.

   CrCl = (140 − 82) × 70 ÷ (72 × 1.6) ≈ 35 mL/min, and the AF label dose for CrCl 15–50 mL/min is 15 mg once daily with the evening meal (food is needed for full absorption). The 20 mg dose is for CrCl above 50 mL/min. The 10 mg dose is used for VTE prophylaxis or extended VTE prevention, and 15 mg twice daily for 21 days is the initial VTE treatment regimen, not AF stroke prevention.

   A

   Rivaroxaban 10 mg is a VTE prophylaxis or extended-prevention dose, not stroke prevention in AF.

   B

   Correct. Cockcroft-Gault gives about 35 mL/min, and the AF label dose for CrCl 15–50 is 15 mg once daily with the evening meal.

   C

   15 mg twice daily for 21 days is the initial VTE treatment phase, not an AF regimen.

   D

   20 mg with the evening meal is the AF dose for CrCl above 50 mL/min; his is about 35.

6. Case 06

   A 52-year-old man (88 kg) has newly diagnosed nonvalvular atrial fibrillation with hypertension and type 2 diabetes (CHA₂DS₂-VASc 2). He has no valve disease, no bleeding history and no interacting drugs. SCr is 0.8 mg/dL (CrCl about 130 mL/min). He asks for a once-daily DOAC. Which regimen is most appropriate?

   1. AOption A: Edoxaban 60 mg once daily, the usual full dose
   2. BOption B: Rivaroxaban 20 mg once daily with the evening meal
   3. COption C: Edoxaban 30 mg once daily to offset fast clearance
   4. DOption D: Warfarin with an INR goal of 2.0–3.0, checked monthly

   Pick an option: the verdict and a note on every option open here.

   Best answer: B.

   The 2023 ACC/AHA/ACCP/HRS atrial fibrillation guideline prefers a DOAC over warfarin unless the patient has a mechanical valve or moderate-to-severe mitral stenosis. The DOAC must still fit the kidney function. The edoxaban (Savaysa) label carries a boxed warning: in the ENGAGE AF-TIMI 48 trial, patients with CrCl above 95 mL/min had more ischemic strokes on edoxaban 60 mg daily than on warfarin, so it should not be used in them. A dose cut does not solve this. Rivaroxaban (Xarelto) is labeled at 20 mg once daily with the evening meal when CrCl is above 50 mL/min, so it fits a once-daily request at his CrCl of about 130 mL/min.

   A

   The edoxaban label has a boxed warning: do not use it in atrial fibrillation with CrCl above 95 mL/min, since stroke rates rose with 60 mg daily.

   B

   Correct. With CrCl above 50 mL/min, the label dose is 20 mg once daily taken with the evening meal, which meets his once-daily wish.

   C

   A lower dose does not fix the problem. The label says not to use edoxaban at all above CrCl 95 mL/min; 30 mg is for reduced kidney function.

   D

   The 2023 AF guideline prefers a DOAC over warfarin for eligible patients like him. He has no mechanical valve or moderate-to-severe mitral stenosis.