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Editor's Note |

Data for a Common Clinical Dilemma

Mitchell H. Katz, MD
JAMA Intern Med. 2014;174(3):416. doi:10.1001/jamainternmed.2013.13480.
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A patient receiving warfarin for atrial fibrillation experiences worsening of her chronic obstructive pulmonary disease with purulent sputum. You want to start an antibiotic. Her international normalized ratio (INR) has been rock stable at 2.5. Should you adjust the dose of warfarin? Would the answer be different if she was just ill and you were not going to use an antibiotic? Does it depend on the antibiotic? This is a common medicine (warfarin) and a common situation (upper respiratory tract infection), and yet there are no easy real-world answers.


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Fondaparinux is not indicated for treating atrial fibrillation.
Posted on January 21, 2014
David L. Keller, M.D.
Conflict of Interest: None Declared
Since Fondaparinux and enoxaparin are not indicated for treating atrial fibrillation, they cannot be recommended for bridging therapy for stroke prophylaxis while a patient treats an infection with an antibiotic likely to interact dangerously with warfarin. One of the newer oral anti-coagulants might be suitable, but watch for transient changes in the patient's coagulation state.
Flouroquinolones interact to increase INR
Posted on January 21, 2014
David L. Keller, MD
Conflict of Interest: None Declared
Respiratory flouroquinolones should be mentioned among those antibiotics which interact with warfarin to increase INR. For patients requiring these, bridging therapy with parenteral anticoagulation agents like fondaparinux may be an option. Newer oral anticoagulants would still be subject to emesis by patients with nausea.
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