International normalized ratio

The international normalized ratio (INR) is a method to standardize repotting of the prothrombin time, using the formula, INR = (PTpatie t/PTcontroi)ISI, where PT indicates the prothrombin times (for the patient and the laboratory control), and ISI indicates the international sensitivity index, a value that varies, depending upon the thromboplastin reagent and laboratory instrument used to initiate and detect clot formation, respectively. 

Before administering the first dose of warfarin, die nurse questions the patient about all drags taken during the previous 2 to 3 weeks (if the patient was recendy admitted to the hospital). If the patient took any drug before admission, the nurse notifies the primary healdi care provider before the first dose is administered. Usually, the prothrombin time (PT) is ordered and die international normalized ratio (INR) determined before tiierapy is started. The first dose of warfarin is not given until blood for a baseline PT/ INR is drawn. The dosage is individualized based on die results of the PT or die INR. 

DISPLAY 44-1 Understanding Prothrombin Time and International Normalized Ratio... 

Jones MS, Pontzer JF, DelCurto B, Badgett CA, Sather MR. Integrating interactive voice response system and web based systems to support home international normalization ratio testing. Clin Trials 2005 2 S73. 

Monotherapy to achieve an international normalized ratio (INR) between 2.5 and 3.5... 

Management of Elevated International Normalized Ratio (INR) in Patients Receiving Warfarin Pharmacotherapy... 

Patient is coagulopathic or has recently received an oral anticoagulant (e.g., warfarin) and has an elevated international normalized ratio (INR) >1.4... 

Check complete blood count, prothrombin time, international normalization ratio, activated partial thromboplastin time, fibrinogen levels... 

Vitamin K content of enteral nutrition formulas may affect pharmacological activity. Monitor and titrate dose to maintain therapeutic international normalized ratio (INR)... 

Baseline complete blood count (CBC) and coagulation tests (activated partial thromboplastin time and International Normalized Ratio) should be obtained, as most patients will receive antithrombotic therapy, which increases the risk for bleeding. 

Either UFH or LMWH should be administered to patients with NSTE ACS. Therapy should be continued for up to 48 hours or until the end of the angiography or PCI procedure. In patients initiating warfarin therapy, UFH or LMWHs should be continued until the International Normalized Ratio (INR) with warfarin is in the therapeutic range for 2 consecutive days. The addition of UFH to aspirin reduces the rate of death or MI in patients with NSTE ACS.47 Enoxaparin was mentioned as preferred over UFH in the 2002 ACC/AHA clinical practice guidelines, as two large clinical trials found a reduction in the combined endpoint of death, MI, or need for PCI in patients... 

ACE, angiotensin-converting enzyme aPTT, activated partial thromboplastin time ARB, angiotensin receptor blocker BP, blood pressure CBC, complete blood count ECC, electrocardiogram HR, heart rate INR, International Normalized Ratio RR, respiratory rate SCr, serum creatinine, TTP, thrombotic thrombocytopenic purpura. 

The majority of patients with AF should receive warfarin therapy (titrated to an International Normalized Ratio of 2 to 3) for stroke prevention, particularly if they have other risk factors for stroke. 

FIGURE 6-9. Decision algorithm for stroke prevention in atrial fibrillation.27 Risk factors for stroke prior transient ischemic attack or stroke hypertension heart failure rheumatic heart valve disease prosthetic heart valve. Target International Normalized Ratio = 2.5 (range 2 to 3). 

FIGURE 7-5. Treatment approach for patients with VTE. INR, International Normalized Ratio IV, intravenous LMWH, low-molecular-weight heparin PO, oral SC, subcutaneous UFH, unfractionated heparin VTE, venous thromboembolism. (Adapted from Nutescu EA. Emerging options in the treatment of venous thromboembolism. Am J Health Syst Pharm 2004 61 (Suppl 7) S16, with permission.)... 

HIT, heparin-induced thrombocytopenia INR, International Normalized Ratio LMWHs, low-molecular-weight heparins PT, prothrombin time UFH, unfractionated heparin. 

FIGURE 7-9. Initiation of warfarin therapy. INR, International Normalized Ratio PT, prothrombin time. (Reproduced from Haines ST, Zeolla M, Witt DM. Venous thromboembolism. In DiPiro JT, Talbert RL, Yee GC, et al, (eds.) Pharmacotherapy A Pathophysiologic Approach. 6th ed. New York McGraw-Hill 2005 391, with permission.)... 

Warfarin has not been adequately studied in non-cardioembolic stroke, but it is often recommended in patients after antiplatelet agents fail. One small retrospective study suggests that warfarin is better than aspirin.30 More recent clinical trials have not found oral anticoagulation in those patients without atrial fibrillation or carotid stenosis to be better than antiplatelet therapy. In the majority of patients without atrial fibrillation, antiplatelet therapy is recommended over warfarin. In patients with atrial fibrillation, long-term anticoagulation with warfarin is recommended and is effective in both primary and secondary prevention of stroke.12 The goal International Normalized Ratio (INR) for this indication is 2 to 3. 

ACE-I, angiotensin-converting enzyme inhibitor ARB, angiotensin receptor blocker INR, International Normalized Ratio IV, intravenous t-PA, tissue plasminogen activator. 

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