A 62-year-old man with a history of a mechanical mitral valve replacement comes to the out… — USMLE Step 3

A 62-year-old man with a history of a mechanical mitral valve replacement comes to the outpatient clinic for routine coagulation monitoring. Five days ago, he was evaluated at an urgent care center for a purulent skin infection and was started on oral trimethoprim-sulfamethoxazole. His current medications include warfarin, metoprolol, and lisinopril. The patient reports feeling well and denies any epistaxis, hematuria, melena, or easy bruising. Vital signs are within normal limits. Physical examination reveals a healing area of cellulitis on the right lower extremity, with no evidence of petechiae or ecchymoses.

Laboratory results obtained today:

Test	Result
Hemoglobin	$13.8$ g/dL
Platelets	$210,000$ /mm³
Serum creatinine	$1.1$ mg/dL
INR	$7.2$

Which of the following is the most appropriate next step in the management of this patient?

Omit the next 1 to 2 doses of warfarin and repeat the INR in 24 to 48 hoursAnswer
B
Administer oral phytonadione and reduce the weekly warfarin maintenance dose
C
Administer intravenous phytonadione and four units of fresh frozen plasma
D
Continue the current warfarin regimen and substitute trimethoprim-sulfamethoxazole with cephalexin
E
Discontinue warfarin entirely and initiate a direct oral anticoagulant

Answer

The most appropriate next step is to omit the next 1 to 2 doses of warfarin and repeat the INR in 24 to 48 hours.

In a patient taking warfarin who presents with a supratherapeutic INR between

4.5

and

10.0

and no evidence of bleeding, the most appropriate management is to omit the next

1

2

doses of warfarin, monitor the INR closely, and resume therapy at an appropriately adjusted (lower) dose once the INR falls into the therapeutic range. The target INR for a mechanical mitral valve is typically

2.5

3.5

. The recent initiation of trimethoprim-sulfamethoxazole caused this derangement via inhibition of CYP2C9, which metabolizes warfarin. Because there is no active bleeding, the administration of active reversal agents is not indicated.

Step-by-Step Solution

Evaluate the patient for signs of active or life-threatening bleeding.

The patient is completely asymptomatic with no signs of bleeding on history or physical examination.

The presence of major bleeding dictates an immediate shift toward active reversal agents (e.g., prothrombin complex concentrate, FFP, intravenous vitamin K).

Identify the cause of the laboratory derangement.

The patient was recently started on trimethoprim-sulfamethoxazole.

Trimethoprim-sulfamethoxazole inhibits the cytochrome P450 2C9 (CYP2C9) enzyme, which decreases the clearance of the more active S-enantiomer of warfarin, significantly elevating the INR.

Apply guideline-directed management for the specific INR range.

The INR is 7.2 (which falls into the 4.5 to 10.0 range).

For an asymptomatic patient with an INR between 4.5 and 10.0, current guidelines recommend holding 1 to 2 doses of warfarin and monitoring closely, without administering routine vitamin K.

Key Concept

Management of supratherapeutic INR in asymptomatic patients

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