Warfarin Dosage

This dosage information may not include all the information needed to use Warfarin safely and effectively. See additional information for Warfarin.

The information at Drugs.com is not a substitute for medical advice. ALWAYS consult your doctor or pharmacist.

Usual Adult Dose for Congestive Heart Failure

Initial: 2 to 5 mg orally or intravenously once a day for 1 to 2 days, then adjust dose according to results of the International Normalized Ratio (INR) or prothrombin time (PT).

Maintenance: the usual maintenance dose ranges from 2 to 10 mg orally or intravenously once a day.

Usual Adult Dose for Thromboembolic Stroke Prophylaxis

Initial: 2 to 5 mg orally or intravenously once a day for 1 to 2 days, then adjust dose according to results of the International Normalized Ratio (INR) or prothrombin time (PT).

Maintenance: the usual maintenance dose ranges from 2 to 10 mg orally or intravenously once a day.

Usual Adult Dose for Myocardial Infarction

Initial: 2 to 5 mg orally or intravenously once a day for 1 to 2 days, then adjust dose according to results of the International Normalized Ratio (INR) or prothrombin time (PT).

Maintenance: the usual maintenance dose ranges from 2 to 10 mg orally or intravenously once a day.

The duration of therapy is usually three months following acute myocardial infarction.

Usual Adult Dose for Prevention of Thromboembolism in Atrial Fibrillation

Initial: 2 to 5 mg orally or intravenously once a day for 1 to 2 days, then adjust dose according to results of the International Normalized Ratio (INR) or prothrombin time (PT).

Maintenance: the usual maintenance dose ranges from 2 to 10 mg orally or intravenously once a day.

If cardioversion is planned, anticoagulant therapy is usually initiated two to four weeks prior to cardioversion and is continued for two to four weeks following successful cardioversion. If cardioversion is not planned and this patient has complicated atrial fibrillation (atrial fibrillation associated with underlying heart disease) the duration of therapy is typically lifelong.

Usual Adult Dose for Deep Vein Thrombosis Prophylaxis after Hip Replacement Surgery

Initial: 2 to 5 mg orally or intravenously once a day for 1 to 2 days, then adjust dose according to results of the International Normalized Ratio (INR) or prothrombin time (PT).

Maintenance: the usual maintenance dose ranges from 2 to 10 mg orally or intravenously once a day.

The duration of anticoagulant therapy for a first-time deep venous thrombosis is usually 3 to 12 months, depending on the reversibility of the condition which may have predisposed this patient to thrombosis. For patients with a first episode of DVT secondary to a reversible risk factor, 3 months of warfarin therapy is recommended. For patients with a first episode of idiopathic DVT, at least 6 to 12 months of treatment is recommended. For patients with two or more episodes of documented DVT, indefinite treatment with warfarin is recommended. For patients with a first episode of DVT who have documented antiphospholipid antibodies or who have two or more thrombophilic conditions, treatment for 12 months is recommended and indefinite therapy is suggested. For patients with a first episode of DVT who have documented deficiency of Protein C or Protein S, deficiency of antithrombin, or the Factor V Leiden or prothrombin 20210 gene mutation, homocystinemia, or high Factor VIII levels, treatment for 6 to 12 months is recommended and indefinite therapy is suggested for idiopathic thrombosis.

Usual Adult Dose for Deep Vein Thrombosis - First Event

Initial: 2 to 5 mg orally or intravenously once a day for 1 to 2 days, then adjust dose according to results of the International Normalized Ratio (INR) or prothrombin time (PT).

Maintenance: the usual maintenance dose ranges from 2 to 10 mg orally or intravenously once a day.

The duration of anticoagulant therapy for a first-time deep venous thrombosis is usually 3 to 12 months, depending on the reversibility of the condition which may have predisposed this patient to thrombosis. For patients with a first episode of DVT secondary to a reversible risk factor, 3 months of warfarin therapy is recommended. For patients with a first episode of idiopathic DVT, at least 6 to 12 months of treatment is recommended. For patients with two or more episodes of documented DVT, indefinite treatment with warfarin is recommended. For patients with a first episode of DVT who have documented antiphospholipid antibodies or who have two or more thrombophilic conditions, treatment for 12 months is recommended and indefinite therapy is suggested. For patients with a first episode of DVT who have documented deficiency of Protein C or Protein S, deficiency of antithrombin, or the Factor V Leiden or prothrombin 20210 gene mutation, homocystinemia, or high Factor VIII levels, treatment for 6 to 12 months is recommended and indefinite therapy is suggested for idiopathic thrombosis.

Usual Adult Dose for Deep Vein Thrombosis - Recurrent Event

Initial: 2 to 5 mg orally or intravenously once a day for 1 to 2 days, then adjust dose according to results of the International Normalized Ratio (INR) or prothrombin time (PT).

Maintenance: the usual maintenance dose ranges from 2 to 10 mg orally or intravenously once a day.

The duration of anticoagulant therapy for a first-time deep venous thrombosis is usually 3 to 12 months, depending on the reversibility of the condition which may have predisposed this patient to thrombosis. For patients with a first episode of DVT secondary to a reversible risk factor, 3 months of warfarin therapy is recommended. For patients with a first episode of idiopathic DVT, at least 6 to 12 months of treatment is recommended. For patients with two or more episodes of documented DVT, indefinite treatment with warfarin is recommended. For patients with a first episode of DVT who have documented antiphospholipid antibodies or who have two or more thrombophilic conditions, treatment for 12 months is recommended and indefinite therapy is suggested. For patients with a first episode of DVT who have documented deficiency of Protein C or Protein S, deficiency of antithrombin, or the Factor V Leiden or prothrombin 20210 gene mutation, homocystinemia, or high Factor VIII levels, treatment for 6 to 12 months is recommended and indefinite therapy is suggested for idiopathic thrombosis.

Usual Adult Dose for Deep Vein Thrombosis Prophylaxis after Knee Replacement Surgery

Initial: 2 to 5 mg orally or intravenously once a day for 1 to 2 days, then adjust dose according to results of the International Normalized Ratio (INR) or prothrombin time (PT).

Maintenance: the usual maintenance dose ranges from 2 to 10 mg orally or intravenously once a day.

The duration of anticoagulant therapy for a first-time deep venous thrombosis is usually 3 to 12 months, depending on the reversibility of the condition which may have predisposed this patient to thrombosis. For patients with a first episode of DVT secondary to a reversible risk factor, 3 months of warfarin therapy is recommended. For patients with a first episode of idiopathic DVT, at least 6 to 12 months of treatment is recommended. For patients with two or more episodes of documented DVT, indefinite treatment with warfarin is recommended. For patients with a first episode of DVT who have documented antiphospholipid antibodies or who have two or more thrombophilic conditions, treatment for 12 months is recommended and indefinite therapy is suggested. For patients with a first episode of DVT who have documented deficiency of Protein C or Protein S, deficiency of antithrombin, or the Factor V Leiden or prothrombin 20210 gene mutation, homocystinemia, or high Factor VIII levels, treatment for 6 to 12 months is recommended and indefinite therapy is suggested for idiopathic thrombosis.

Usual Adult Dose for Prosthetic Heart Valves - Tissue Valves

Initial: 2 to 5 mg orally or intravenously once a day for 1 to 2 days, then adjust dose according to results of the International Normalized Ratio (INR) or prothrombin time (PT).

Maintenance: the usual maintenance dose ranges from 2 to 10 mg orally or intravenously once a day.

The duration of anticoagulant therapy following tissue heart valve replacement surgery is usually 6 to 12 weeks. The duration of therapy may be longer in patients with a tissue valve in the mitral location, particularly in the presence of a large left atrium and/or atrial fibrillation. In patients who receive a mechanical heart valve, lifelong anticoagulant therapy is usually needed and low dose aspirin (80 to 100 mg/day) may be added in higher risk patients.

Usual Adult Dose for Prosthetic Heart Valves - Mechanical Valves

Initial: 2 to 5 mg orally or intravenously once a day for 1 to 2 days, then adjust dose according to results of the International Normalized Ratio (INR) or prothrombin time (PT).

Maintenance: the usual maintenance dose ranges from 2 to 10 mg orally or intravenously once a day.

The duration of anticoagulant therapy following tissue heart valve replacement surgery is usually 6 to 12 weeks. The duration of therapy may be longer in patients with a tissue valve in the mitral location, particularly in the presence of a large left atrium and/or atrial fibrillation. In patients who receive a mechanical heart valve, lifelong anticoagulant therapy is usually needed and low dose aspirin (80 to 100 mg/day) may be added in higher risk patients.

Usual Adult Dose for Pulmonary Embolism - First Event

Initial: 2 to 5 mg orally or intravenously once a day for 1 to 2 days, then adjust dose according to results of the International Normalized Ratio (INR) or prothrombin time (PT).

Maintenance: the usual maintenance dose ranges from 2 to 10 mg orally or intravenously once a day.

The duration of anticoagulant therapy for a first occurrence of pulmonary embolism is 3 to 12 months depending on the reversibility of the condition which may have predisposed this patient to thrombosis. For patients with a first episode of DVT or PE secondary to a reversible risk factor, 3 months of warfarin therapy is recommended. For patients with a first episode of idiopathic DVT or PE, at least 6 to 12 months of treatment is recommended. For patients with two or more episodes of documented DVT or PE, indefinite treatment with warfarin is recommended. For patients with a first episode of DVT or PE who have documented antiphospholipid antibodies or who have two or more thrombophilic conditions, treatment for 12 months is recommended and indefinite therapy is suggested. For patients with a first episode of DVT or PE who have documented deficiency of Protein C or Protein S, deficiency of antithrombin, or the Factor V Leiden or prothrombin 20210 gene mutation, homocystinemia, or high Factor VIII levels, treatment for 6 to 12 months is recommended and indefinite therapy is suggested for idiopathic thrombosis.

Usual Adult Dose for Pulmonary Embolism - Recurrent Event

Initial: 2 to 5 mg orally or intravenously once a day for 1 to 2 days, then adjust dose according to results of the International Normalized Ratio (INR) or prothrombin time (PT).

Maintenance: the usual maintenance dose ranges from 2 to 10 mg orally or intravenously once a day.

The duration of anticoagulant therapy for a first occurrence of pulmonary embolism is 3 to 12 months depending on the reversibility of the condition which may have predisposed this patient to thrombosis. For patients with a first episode of DVT or PE secondary to a reversible risk factor, 3 months of warfarin therapy is recommended. For patients with a first episode of idiopathic DVT or PE, at least 6 to 12 months of treatment is recommended. For patients with two or more episodes of documented DVT or PE, indefinite treatment with warfarin is recommended. For patients with a first episode of DVT or PE who have documented antiphospholipid antibodies or who have two or more thrombophilic conditions, treatment for 12 months is recommended and indefinite therapy is suggested. For patients with a first episode of DVT or PE who have documented deficiency of Protein C or Protein S, deficiency of antithrombin, or the Factor V Leiden or prothrombin 20210 gene mutation, homocystinemia, or high Factor VIII levels, treatment for 6 to 12 months is recommended and indefinite therapy is suggested for idiopathic thrombosis.

Usual Adult Dose for Chronic Central Venous Catheterization

1 mg orally or intravenously once a day

Therapy should be initiated three days before insertion of the catheter. No changes in coagulation values are expected with this low dose.

Renal Dose Adjustments

No adjustment recommended

Liver Dose Adjustments

Liver failure patients may be at an increased risk for bleeding complications. Cautious use of warfarin in these patients is recommended.

Dose Adjustments

Dosage adjustments should be made based on the patients PT/INR. Generally, INR values between 2.0 and 3.0 are considered sufficient for patients treated for venous thromboembolism, atrial fibrillation, and bioprosthetic valve replacement. Patients treated for mechanical valve replacement or postmyocardial infarction generally require an INR of 2.5 to 3.5.

Lower initial dosages are recommended in elderly or debilitated patients. In addition, Asian patients may also require a lower initial dosage. Patients with low serum albumin levels (less than 3 g/dL) may be more sensitive to the effects of warfarin and may also require a lower initial dosage.

Genetic variations in the CYP450 2C9 and VKORC1 enzymes can significantly influence a patient's response to warfarin therapy as indicated by the PT/INR. Lower initial doses have been suggested for patients with these genetic variations since these patients are at an increased risk of bleeding. Range of Expected Therapeutic Maintenance Dose Based on CYP450 2C9 and VKORC13 Genotypes:
If VKORC1 GG and CYP450 2C9 *1/*1, then 5 to 7 mg.
If VKORC1 AG and CYP450 2C9 *1/*1, then 5 to 7 mg.
If VKORC1 AA and CYP450 2C9 *1/*1, then 3 to 4 mg.
If VKORC1 GG and CYP450 2C9 *1/*2, then 5 to 7 mg.
If VKORC1 AG and CYP450 2C9 *1/*2, then 3 to 4 mg.
If VKORC1 AA and CYP450 2C9 *1/*2, then 3 to 4 mg.
If VKORC1 GG and CYP450 2C9 *1/*3, then 3 to 4 mg.
If VKORC1 AG and CYP450 2C9 *1/*3, then 3 to 4 mg.
If VKORC1 AA and CYP450 2C9 *1/*3, then 0.5 to 2 mg.
If VKORC1 GG and CYP450 2C9 *2/*2, then 3 to 4 mg.
If VKORC1 AG and CYP450 2C9 *2/*2, then 3 to 4 mg.
If VKORC1 AA and CYP450 2C9 *2/*2, then 0.5 to 2 mg.
If VKORC1 GG and CYP450 2C9 *2/*3, then 3 to 4 mg.
If VKORC1 AG and CYP450 2C9 *2/*3, then 0.5 to 2 mg.
If VKORC1 AA and CYP450 2C9 *2/*3, then 0.5 to 2 mg.
If VKORC1 GG and CYP450 2C9 *3/*3, then 0.5 to 2 mg.
If VKORC1 AG and CYP450 2C9 *3/*3, then 0.5 to 2 mg.
If VKORC1 AA and CYP450 2C9 *3/*3, then 0.5 to 2 mg.
Note: Must also take into account other patient related factors when determining initial dose (e.g., age, body weight, concomitant medications, comorbidities)
Patients with CYP450 2C9 *1/*3, *2/*2, *2/*3, and *3/*3 alleles may take up to 4 weeks to achieve maximum INR with a given dose regimen.

The results of one study suggest that following heart valve replacement, patients are more sensitive to warfarin and subject to an exaggerated warfarin response. The increased sensitivity may be due to a reduction in clotting factors and/or hypoalbuminemia as a result of cardiopulmonary bypass. A lower warfarin dose during the initiation of therapy has been suggested with frequent monitoring as the enhanced sensitivity decreases with time. Patients are likely to require an increase in dose during the follow-up period due to recovery from perioperative physiologic changes.

Precautions

Anticoagulation therapy of each patient is a highly individualized matter. The dosing of warfarin should be individualized based on the patient's response as indicated by the prothrombin time (PT)/International Normalized Ratio (INR). Warfarin has a narrow therapeutic index, numerous factors such as other medications, dietary vitamin K, botanicals, and genetic variations, particularly in the CYP450 2C9 and VKORC1 enzymes, can significantly influence a patient's response to warfarin therapy. Ongoing warfarin therapy should be guided by continued periodic PT/INR monitoring.

The risk of bleeding is high during initiation of therapy. Use of loading doses is not recommended. Loading doses may increase the incidence of hemorrhage and do not offer more rapid protection against the formation of thrombi. An INR of greater than 4.0 appears to provide no additional therapeutic benefit in most patients and is associated with a higher risk of bleeding. Lower initial doses have been suggested for patients with genetic variations in CYP450 2C9 and VKORC1 enzymes as well as for the elderly, debilitated patients, and in any patient with the potential to exhibit greater than expected PT/INR responses to warfarin. To minimize the risk of bleeding, patients should be instructed about prevention measures and to report immediately to physicians signs and symptoms of bleeding.

The response to warfarin may be exaggerated (i.e., unpredictable PT/INR variability) in patients with moderate to severe hepatic or renal dysfunction, uncontrolled hypertension and/or diabetes, congestive heart failure, vasculitis, and in patients 60 years of age or older. In addition, warfarin should be used with caution in patients with heparin-induced thrombocytopenia, infectious diseases, disturbances of intestinal flora, trauma, or indwelling catheters. Under any of these circumstances, more frequent monitoring of PT/INR, a shorter duration of therapy, careful dose adjustment to desired INR, and lower initial and maintenance doses of warfarin have been recommended.

Warfarin can cause fatal or major bleeding, which is the most serious risk associated with the use of warfarin. Less frequently, necrosis and/or gangrene have occurred. Caution should be used when warfarin is administered in any situation where added risk of hemorrhage, necrosis, and/or gangrene is present.

The risk of bleeding may be increased in hemodialysis patients receiving warfarin treatment. The benefit of therapy should be fully assessed prior to treating such patients with warfarin.

Anticoagulation is contraindicated in patients with any localized or general physical condition or personal circumstance in which the risk of hemorrhage may be greater than the potential anticoagulation benefits.

A severe elevation (greater than 50 seconds) in activated partial thromboplastin time (aPTT) with a PT/INR in the desired range has been reported to be an indication of increased risk of postoperative hemorrhage.

Safety and effectiveness have not been established in pediatric patients (less than 18 years of age). However, warfarin has been used in pediatric patients for the prevention and treatment of thromboembolic events. It should be noted that because of difficulty achieving and maintaining therapeutic PT/INR ranges in pediatric patients, more frequent monitoring of PT/INR has been recommended for this patient population.

Dialysis

Data not available

Other Comments

The INR should generally be monitored daily for the first 5 days of therapy, twice weekly for the next 1 to 2 weeks, then weekly for the next 1 to 2 months. If the INR is stable, monitoring may be reduced to 1 to 2 times a month. Consider rechecking the INR within 7 days after beginning or ending any medication known to alter the effect of warfarin.

Genetic testing prior to initiation of warfarin therapy in order to determine if the patient has genetic variations in CYP450 2C9 and VKORC1 enzymes has been suggested.

Although oral warfarin is considered the standard of care for long-term anticoagulation, intravenous warfarin is an effective alternative administration route for patients who cannot receive the oral formulation and cannot be administered subcutaneous low-molecular-weight heparins.

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