Anticoagulation for the PEBC® Exam: Canadian Guidelines and Practice Questions

Anticoagulation questions on the PEBC® Pharmacist Qualifying Examination Part I are rarely about memorizing a mechanism. They ask you to decide who needs an anticoagulant, choose and dose it for kidney function, age and weight, manage it around a procedure, and catch an interaction. With Clinical Care at about half of the exam under Blueprint Ver. 03-2026, these are high-yield marks. See the exam guide for the blueprint breakdown.

This page follows the Canadian Cardiovascular Society and Canadian Heart Rhythm Society (CCS/CHRS) atrial fibrillation guidelines and Thrombosis Canada clinical guides. Canada uses the simple CHADS-65 algorithm rather than the CHA2DS2-VASc score emphasized in US and European material, and Canadian DOAC labelling differs from US labelling in places.

Last reviewed October 18, 2026 · Based on the Pharmacist Qualifying Examination Blueprint, Ver. 03-2026

Who needs anticoagulation in AF: the CCS CHADS-65 algorithm

The algorithm applies to nonvalvular AF (including atrial flutter). Work through it in order and stop at the first yes.

When an OAC is indicated, a DOAC is preferred over warfarin for most patients.
Use warfarin, not a DOAC, with a mechanical heart valve or moderate to severe mitral stenosis.
A high bleeding risk score is a prompt to fix modifiable risks (uncontrolled BP, NSAIDs, alcohol, labile INR), not a reason on its own to withhold anticoagulation. Female sex is not a separate criterion in CHADS-65.

Age 65 or older? Oral anticoagulant (OAC).
Under 65 with any CHADS2 risk factor: prior stroke or TIA, hypertension, heart failure or diabetes? OAC.
None of those, but coronary artery disease or peripheral arterial disease? Antiplatelet therapy (ASA 81 mg daily), driven by the vascular disease rather than the AF.
None of the above? No antithrombotic therapy for stroke prevention.

DOAC dosing for AF

Estimate kidney function with Cockcroft-Gault using actual body weight, as the DOAC trials did. In SI units: CrCl (mL/min) = (140 minus age) × weight (kg) × 1.23 for males, or × 1.04 for females, divided by serum creatinine (µmol/L). Do not substitute eGFR. Recheck kidney function at least yearly, and more often in older or unstable patients.

Apixaban dose reduction uses serum creatinine, not CrCl. A low CrCl alone does not trigger the 2.5 mg dose.
Inappropriate dose reduction is common in practice and is linked to more strokes. Use the full dose unless criteria are met.
Avoid DOACs with strong inducers of both CYP3A4 and P-gp (rifampin, carbamazepine, phenytoin, St John's wort). Dabigatran capsules must not be opened.

Stroke prevention doses in AF (Canadian product monographs; confirm details in the current monograph)
Drug (brand)	Usual dose	Reduced dose when
Apixaban (Eliquis)	5 mg twice daily	2.5 mg twice daily if at least 2 of: age 80 or older, weight 60 kg or less, serum creatinine 133 µmol/L or higher
Rivaroxaban (Xarelto)	20 mg once daily with food	15 mg once daily with food if CrCl 30 to 49 mL/min
Edoxaban (Lixiana)	60 mg once daily	30 mg once daily if any of: CrCl 15 to 50 mL/min, weight 60 kg or less, or certain P-gp inhibitors (for example cyclosporine, dronedarone, erythromycin, ketoconazole)
Dabigatran (Pradaxa)	150 mg twice daily	110 mg twice daily if age 80 or older or at higher bleeding risk; contraindicated if CrCl below 30 mL/min

Perioperative management of DOACs

Thrombosis Canada's approach for elective procedures is based on the PAUSE study: a fixed interruption schedule by drug, kidney function and procedural bleeding risk, with no heparin bridging and no routine preoperative DOAC levels. Day 0 is the day of the procedure.

Restart about 24 hours after a low to moderate bleeding risk procedure and 48 to 72 hours after a high bleeding risk procedure, once hemostasis is secure.
Warfarin is different: it is usually stopped about 5 days before surgery, and bridging is reserved for selected very high thrombotic risk patients such as those with mechanical mitral valves.
Many dental, cataract and minor skin procedures can proceed without interrupting anticoagulation.

Elective interruption of DOACs (illustrative schedule; confirm with the current Thrombosis Canada guide)
Drug	Low to moderate bleeding risk: last dose	High bleeding risk: last dose
Apixaban, edoxaban, rivaroxaban	Day minus 2 (skip 1 day)	Day minus 3 (skip 2 days)
Dabigatran, CrCl 50 mL/min or more	Day minus 2 (skip 1 day)	Day minus 3 (skip 2 days)
Dabigatran, CrCl 30 to 49 mL/min	Day minus 3 (skip 2 days)	Day minus 5 (skip 4 days)

Warfarin: targets, monitoring and interactions

For AF and most VTE, the INR target is 2.0 to 3.0 (target 2.5). Check the INR frequently at initiation, then extend the interval once stable. Counsel on consistent vitamin K intake, alcohol, and checking with the pharmacist before any new drug or natural health product.

When an interacting drug cannot be avoided, check the INR within about 3 to 5 days and adjust. Prefer a non-interacting alternative when one exists.
Reversal: vitamin K plus prothrombin complex concentrate (Octaplex, Beriplex) for warfarin with major bleeding; idarucizumab (Praxbind) for dabigatran.

High-yield warfarin interactions
Effect	Examples
INR up (bleeding risk)	Amiodarone, fluconazole and other azoles, metronidazole, trimethoprim-sulfamethoxazole, some fluoroquinolones and macrolides, regular high dose acetaminophen, acute alcohol excess
INR down (clot risk)	Rifampin, carbamazepine, St John's wort, sudden increase in vitamin K intake, missed doses
Bleeding risk without INR change	NSAIDs, ASA and other antiplatelets, SSRIs and SNRIs

Special populations

Older adults: age is a reason to anticoagulate, not to avoid it. Falls risk rarely outweighs stroke benefit. Check dose reduction criteria carefully.
Kidney disease: dabigatran is the most kidney dependent (contraindicated below 30 mL/min). With severe kidney failure or dialysis, warfarin is the usual choice; check product monographs for limits.
Pregnancy: warfarin is teratogenic and DOACs are not recommended; low molecular weight heparin is preferred.
AF with stable coronary disease (more than a year after an event or stent): an OAC alone is generally enough; do not add ASA routinely.
Comorbidities: hypertension and diabetes are CHADS-65 risk factors. See the hypertension and diabetes reviews.

Red flags and when to refer

Signs of major bleeding: black or bloody stools, vomiting blood, blood in urine, severe headache, unusual bruising, dizziness or fainting.
Stroke symptoms (face drooping, arm weakness, speech difficulty): call 911 immediately.
INR well above range, any head injury while anticoagulated, or a sudden fall in kidney function on a DOAC.

Common exam traps

Applying CHA2DS2-VASc and treating female sex as a risk point. CHADS-65 starts with age 65.
Giving ASA for stroke prevention in AF. ASA is only for the CAD or arterial disease branch of the algorithm.
Reducing apixaban for age alone or for a low CrCl. It needs two of three criteria.
Using eGFR, or ideal body weight without reason, instead of Cockcroft-Gault with actual weight for DOAC dosing.
Forgetting that rivaroxaban 15 and 20 mg doses must be taken with food.
Bridging a DOAC with enoxaparin before surgery.
Choosing a DOAC for a patient with a mechanical valve.

Practice questions

Original questions written for this page. Answer each one before you open the explanation.

Question 1Atrial fibrillation

Providing Care: Clinical Care

A 61-year-old woman is newly diagnosed with nonvalvular atrial fibrillation. Her history includes hypertension treated with an ARB. She has no diabetes, heart failure, prior stroke or coronary disease. CrCl is 85 mL/min.

According to the CCS CHADS-65 algorithm, which is the most appropriate stroke prevention therapy?

A.No antithrombotic therapy because she is under 65
B.ASA 81 mg daily
C.An oral anticoagulant, preferably a DOAC
D.ASA 81 mg plus clopidogrel 75 mg daily
E.Warfarin, because it is preferred for new starts

Show answer and explanation

Answer: C

She is under 65, so the next step asks about CHADS2 risk factors. Hypertension is one of them, which makes her eligible for an oral anticoagulant, and Canadian guidance prefers a DOAC over warfarin for nonvalvular AF.

Why the other options are wrong

A:Being under 65 only leads to no therapy if she also has none of the CHADS2 risk factors; she has hypertension.
B:ASA is reserved for patients with coronary or arterial disease and no other indication for an OAC; it is not adequate stroke prevention in AF.
D:Dual antiplatelet therapy is less effective than anticoagulation for AF stroke prevention and still carries meaningful bleeding risk.
E:DOACs are preferred over warfarin unless she had a mechanical valve or moderate to severe mitral stenosis.

Reference: CCS/CHRS Comprehensive Guidelines for the Management of Atrial Fibrillation (2020)

Question 2Calculations

Providing Care: Clinical Care

A 78-year-old man with nonvalvular AF is starting rivaroxaban. He weighs 70 kg and his serum creatinine is 160 µmol/L.

Using the Cockcroft-Gault equation, which rivaroxaban regimen is most appropriate?

A.20 mg once daily with food
B.15 mg once daily with food
C.10 mg once daily
D.2.5 mg twice daily
E.Rivaroxaban is contraindicated at this kidney function

Show answer and explanation

Answer: B

CrCl = (140 minus 78) × 70 × 1.23 ÷ 160 = 62 × 70 × 1.23 ÷ 160 = 5338 ÷ 160, which is about 33 mL/min. For AF, a CrCl of 30 to 49 mL/min calls for rivaroxaban 15 mg once daily, taken with food to ensure absorption.

Why the other options are wrong

A:20 mg once daily is for CrCl of 50 mL/min or more; his CrCl is about 33 mL/min.
C:10 mg once daily is a VTE prophylaxis or extended VTE prevention dose, not an AF stroke prevention dose.
D:2.5 mg twice daily is the vascular protection dose used with ASA in stable coronary or peripheral artery disease, not AF.
E:A CrCl of about 33 mL/min is above the level where rivaroxaban becomes not recommended; it requires the reduced dose instead.

Reference: Thrombosis Canada clinical guide: Rivaroxaban (Xarelto); Xarelto Canadian product monograph

Question 3Atrial fibrillation

Providing Care: Clinical Care

An 81-year-old woman with nonvalvular AF is starting apixaban. She weighs 64 kg and her serum creatinine is 118 µmol/L, giving a Cockcroft-Gault CrCl of about 33 mL/min. She takes no interacting medications.

Which apixaban dose is most appropriate?

A.2.5 mg twice daily because she is over 80
B.5 mg twice daily
C.2.5 mg twice daily because her CrCl is below 50 mL/min
D.2.5 mg once daily
E.Apixaban should be avoided; use dabigatran 150 mg twice daily

Show answer and explanation

Answer: B

For AF, apixaban is reduced to 2.5 mg twice daily only when at least two of three criteria are met: age 80 or older, weight 60 kg or less, or serum creatinine 133 µmol/L or higher. She meets only the age criterion, so the full 5 mg twice daily dose is correct. CrCl is not one of the apixaban criteria.

Why the other options are wrong

A:Age alone is only one of the three criteria; two are required for dose reduction.
C:Apixaban dose reduction in AF is based on serum creatinine, not CrCl. Underdosing raises stroke risk.
D:Once daily dosing is never an AF regimen for apixaban, which has a short half-life.
E:Dabigatran is the most kidney dependent DOAC, and at age 80 or older the Canadian dose is 110 mg twice daily, so 150 mg would be inappropriate.

Reference: Thrombosis Canada clinical guide: Apixaban (Eliquis); Eliquis Canadian product monograph

Question 4Perioperative anticoagulation

Providing Care: Clinical Care

A 70-year-old man takes apixaban 5 mg twice daily for AF (CrCl 72 mL/min). He is scheduled for an elective total hip replacement, considered a high bleeding risk procedure, on Monday morning.

Which perioperative plan is most appropriate?

A.Take the last dose Sunday evening and resume Monday night
B.Take the last dose on Friday, no heparin bridging, and resume full dose 48 to 72 hours after surgery once hemostasis is secure
C.Stop apixaban 5 days before and bridge with therapeutic enoxaparin
D.Continue apixaban without interruption
E.Stop apixaban 7 days before and check an anti-Xa level the morning of surgery

Show answer and explanation

Answer: B

For apixaban with normal kidney function and a high bleeding risk procedure, the PAUSE based approach used by Thrombosis Canada omits two days before surgery, so the last dose is on day minus 3 (Friday for a Monday procedure). Bridging is not needed because DOAC levels fall quickly, and full dose resumes 48 to 72 hours after high bleeding risk surgery.

Why the other options are wrong

A:Stopping the evening before is too short for a high bleeding risk procedure, and same day resumption raises bleeding risk.
C:Heparin bridging increases bleeding without reducing thromboembolism in DOAC users; 5 day interruption is a warfarin pattern.
D:Uninterrupted anticoagulation is only reasonable for minimal bleeding risk procedures, not a hip replacement.
E:A 7 day hold leaves him unprotected for longer than needed, and routine preoperative levels are not recommended.

Reference: Thrombosis Canada clinical guide: NOACs/DOACs Perioperative Management; PAUSE study (JAMA Intern Med 2019)

Question 5Warfarin interactions

Providing Care: Clinical Care

A 74-year-old woman on warfarin for AF has had a stable INR of 2.3 to 2.7 for a year. She now has symptoms of uncomplicated cystitis and her physician calls to prescribe trimethoprim-sulfamethoxazole. Her CrCl is 58 mL/min and she has no allergies.

What is the most appropriate recommendation?

A.Use trimethoprim-sulfamethoxazole with no change in monitoring
B.Recommend nitrofurantoin instead, since it does not meaningfully affect the INR
C.Use trimethoprim-sulfamethoxazole and double the warfarin dose during the course
D.Recommend metronidazole instead

Show answer and explanation

Answer: B

Trimethoprim-sulfamethoxazole inhibits warfarin metabolism (CYP2C9) and can raise the INR sharply, increasing bleeding risk. Nitrofurantoin is a first-line option for uncomplicated cystitis, is suitable at her kidney function, and has no clinically important warfarin interaction, so switching the antibiotic avoids the problem.

Why the other options are wrong

A:This combination commonly raises the INR within days; it would at least need early INR monitoring, and a safer alternative exists.
C:The interaction increases warfarin effect, so doubling the dose would greatly increase bleeding risk.
D:Metronidazole is not a treatment for cystitis and also markedly increases the INR.

Reference: Thrombosis Canada clinical guide: Warfarin; Warfarin drug interaction references (Canadian product monograph)

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Frequently asked questions

Why does Canada use CHADS-65 instead of CHA2DS2-VASc?

CHADS-65 is simpler and, in practice, identifies almost the same patients for anticoagulation. Anyone 65 or older, or younger with stroke or TIA, hypertension, heart failure or diabetes, should receive an oral anticoagulant.

Which kidney function estimate should I use for DOAC dosing?

Cockcroft-Gault creatinine clearance with actual body weight, because that is what the DOAC trials and Canadian product monographs use. The exception is apixaban for AF, where dose reduction uses age, weight and serum creatinine directly.

Do DOACs need bridging before surgery?

No. Thrombosis Canada guidance based on the PAUSE study uses a short, fixed interruption by drug, kidney function and bleeding risk, with no heparin bridging.

Which warfarin interactions come up most often?

Antimicrobials (trimethoprim-sulfamethoxazole, metronidazole, fluconazole), amiodarone, enzyme inducers such as rifampin and carbamazepine, and anything that adds bleeding risk such as NSAIDs or antiplatelets.

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