NAPLEX Question of the Week: Dosing Matters

I often get questions from my students before exams asking "Do I have to know how to dose XYZ medication"? Chances are on rotations you have seen how important knowledge of appropriate dosing is for clinical practice. Today's question of the week involves dosing a crucial drug class: Anticoagulants.
NAPLEX Question of the Week: Dosing Matters

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CG is a 57 year old male admitted to the emergency department and  diagnosed with a new pulmonary embolism (hemodynamically stable). Past medical history is significant for diabetes mellitus, hypertension, hyperlipidemia, and osteoarthritis. Labs upon admission are WNL. He weighs 80kg, is 6'0" tall and has NKDA. He initially receives enoxaparin 80mg SQ BID for therapy. On day 3 of hospitalization the team wishes to transition him to  a DOAC instead of warfarin therapy. Which of the following DOAC regimens is appropriate to transition CG from his enoxaparin assuming he can afford therapy?

A. Rivaroxaban 20mg orally once daily with evening meal

B. Apixaban 10mg orally twice daily for 7 days, followed by 5mg orally twice daily

C. Dabigatran 150mg orally twice daily

D. Edoxaban 30mg orally once daily

Answer Explanation:

While dosing is important for all medications, some classes have more risk than others when dosed inappropriately such as anticoagulants. Direct oral anticoagulants or "DOACs" have been increasingly used in recent years since approval of dabigatran (Pradaxa) nearly 10 years ago. There are a number of different reasons for this increase including less drug/drug and drug/food interactions compared to warfarin, less monitoring of anticoagulant effect, and significant clinical experience since approval of many of these agents. Dosing of DOACs is different depending on agent, renal function, and indication. It is important to carefully assess dosing schemes to ensure the appropriate dosage is given to the patient.

Answer A is incorrect. Rivaroxaban (Xarelto) was the second DOAC approved and has had significant use since approval. This answer is incorrect as the correct dosage for patients with new venous thromboembolism is 15mg BID for 3 weeks, then 20mg daily. Only in atrial fibrillation can 20mg once daily be initiated from the beginning assuming normal renal function.

Answer B is correct. Apixaban (Eliquis) is given at the 10mg BID dosage for 7 days, followed by 5mg BID in patients with venous thromboembolism.

Answer C is incorrect. While this is the correct dosage for dabigatran (Pradaxa) for patients with venous thromboembolism, only patients who have received at least 5 days of parenteral anticoagulation may be switched to dabigatran. CG has only received 3 days of therapy and therefore is not eligible yet for a switch.

Answer D is incorrect. Edoxaban similar to dabigatran requires at least 5 days of parenteral therapy before initiation. Additionally, the treatment dose should be 60mg daily, not 30mg daily which is only appropriate for patients with a Clcr between 15 and 50 ml/min.

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