Should enoxaparin be started in a patient with a history of stroke and an INR of 1.6?

Management of Subtherapeutic INR in a Patient with History of Stroke

Enoxaparin should be started immediately in this patient with a history of stroke and a subtherapeutic INR of 1.6, as bridging anticoagulation is necessary to reduce the risk of recurrent stroke while waiting for the warfarin dose adjustment to take effect.

Background and Risk Assessment

• The patient has a history of stroke and is currently on warfarin therapy with a subtherapeutic INR of 1.6 (previous INR was 1.8), indicating inadequate anticoagulation despite an 11% increase in warfarin dose 1
• Patients with ischemic stroke or TIA and subtherapeutic INR are at significantly increased risk for recurrent ischemic events 2
• An INR <2.0 is strongly associated with increased risk of ischemia in patients on warfarin therapy 2

Evidence for Bridging Anticoagulation

• For patients with a history of stroke who require anticoagulation, the American Heart Association/American Stroke Association guidelines recommend maintaining an INR of 2.0-3.0 to reduce the risk of recurrent stroke 1
• Studies show that patients with poor INR control (<60% time in therapeutic range) have significantly higher rates of stroke or systemic embolism (2.10% annually) compared to those with good INR control (1.07%) 3
• When INR falls below 2.0 in high-risk patients (such as those with prior stroke), bridging with low molecular weight heparin is appropriate until therapeutic anticoagulation is achieved 1

Specific Recommendations for This Patient

• Initiate enoxaparin at 1 mg/kg subcutaneously twice daily as bridging therapy 4, 5
• Continue the increased warfarin dose as prescribed (11% increase) 1
• Recheck INR in one week as planned 1, 3
• Continue enoxaparin until the INR reaches the therapeutic range of 2.0-3.0 1

Safety and Efficacy of Enoxaparin

• Enoxaparin has been shown to be safe and effective in patients with acute ischemic stroke 5, 6
• The PREVAIL study demonstrated that enoxaparin had a better clinical benefit-to-risk ratio compared to unfractionated heparin in patients with acute ischemic stroke 5
• Enoxaparin is easier to administer and monitor compared to intravenous heparin 4

Important Considerations

• Mortality, major bleeding, myocardial infarction, and stroke rates are all directly related to INR control, with poor control significantly increasing these risks 3
• No patient with an INR ≥3.6 was found to have ischemia in observational studies, but an INR of 1.6 places this patient at high risk 2
• The risk of recurrent stroke outweighs the bleeding risk in this scenario, especially given the patient's history of stroke 1

Monitoring Recommendations

• Monitor for signs of bleeding while on dual anticoagulation therapy (enoxaparin plus warfarin) 5
• Continue enoxaparin until the INR is consistently in the therapeutic range (2.0-3.0) on two consecutive measurements at least 24 hours apart 1
• Consider proton pump inhibitor therapy if the patient has risk factors for gastrointestinal bleeding 1