WARFARIN SODIUM - warfarin sodium tablet
New Horizon Rx Group, LLC
HIGHLIGHTS OF PRESCRIBING INFORMATION
Warfarin Sodium Tablets, USP for oral use
These highlights do not include all the information needed to use warfarin sodium safely and effectively. See full prescribing information for warfarin sodium.
warfarin sodium (warfarin sodium) TABLET for ORAL use.
Initial U.S. Approval: 2006
WARNING: BLEEDING RISK
See full prescribing information for complete boxed warning.
RECENT MAJOR CHANGES
INDICATIONS AND USAGE
Warfarin sodium tablets, USP are vitamin K antagonist indicated for:
Limitation of Use
Warfarin sodium tablets, USP have no direct effect on an established thrombus, nor does it reverse ischemic tissue damage. (1)
DOSAGE AND ADMINISTRATION
DOSAGE FORMS AND STRENGTHS
WARNINGS AND PRECAUTIONS
Most common adverse reactions to warfarin sodium are fatal and nonfatal hemorrhage from any tissue or organ. (6)
To report SUSPECTED ADVERSE REACTIONS, contact New Horizon Rx Group, LLC at 1-855-465-5545 or FDA at 1-800-FDA-1088 or www.fda.gov/medwatch.
USE IN SPECIFIC POPULATIONS
See 17 for PATIENT COUNSELING INFORMATION and Medication Guide.
FULL PRESCRIBING INFORMATION: CONTENTS*
WARNING: BLEEDING RISK
Warfarin sodium tablets, USP are indicated for:
Limitations of Use
Warfarin sodium tablets, USP have no direct effect on an established thrombus, nor does it reverse ischemic tissue damage. Once a thrombus has occurred, however, the goals of anticoagulant treatment are to prevent further extension of the formed clot and to prevent secondary thromboembolic complications that may result in serious and possibly fatal sequelae.
The dosage and administration of warfarin sodium must be individualized for each patient according to the patient’s INR response to the drug. Adjust the dose based on the patient’s INR and the condition being treated. Consult the latest evidence-based clinical practice guidelines from the American College of Chest Physicians (ACCP) to assist in the determination of the duration and intensity of anticoagulation with warfarin sodium [see References (15)].
An INR of greater than 4 appears to provide no additional therapeutic benefit in most patients and is associated with a higher risk of bleeding.
Venous Thromboembolism (including deep venous thrombosis [DVT] and PE)
Adjust the warfarin dose to maintain a target INR of 2.5 (INR range, 2.0 to 3.0) for all treatment durations. The duration of treatment is based on the indication as follows:
In patients with non-valvular AF, anticoagulate with warfarin to target INR of 2.5 (range, 2.0 to 3.0).
Mechanical and Bioprosthetic Heart Valves
Recurrent Systemic Embolism and Other Indications
Oral anticoagulation therapy with warfarin has not been fully evaluated by clinical trials in patients with valvular disease associated with AF, patients with mitral stenosis, and patients with recurrent systemic embolism of unknown etiology. However, a moderate dose regimen (INR 2.0 to 3.0) may be used for these patients.
The appropriate initial dosing of warfarin sodium varies widely for different patients. Not all factors responsible for warfarin dose variability are known, and the initial dose is influenced by:
Select the initial dose based on the expected maintenance dose, taking into account the above factors. Modify this dose based on consideration of patient-specific clinical factors. Consider lower initial and maintenance doses for elderly and/or debilitated patients and in Asian patients [see Use in Specific Populations (8.5) and Clinical Pharmacology (12.3)]. Routine use of loading doses is not recommended as this practice may increase hemorrhagic and other complications and does not offer more rapid protection against clot formation.
Individualize the duration of therapy for each patient. In general, anticoagulant therapy should be continued until the danger of thrombosis and embolism has passed [see Dosage and Administration (2.2)].
Dosing Recommendations without Consideration of Genotype
If the patient’s CYP2C9 and VKORC1 genotypes are not known, the initial dose of warfarin sodium is usually 2 to 5 mg once daily. Determine each patient’s dosing needs by close monitoring of the INR response and consideration of the indication being treated. Typical maintenance doses are 2 to 10 mg once daily.
Dosing Recommendations with Consideration of Genotype
Table 1 displays three ranges of expected maintenance warfarin sodium doses observed in subgroups of patients having different combinations of CYP2C9 and VKORC1 gene variants [see Clinical Pharmacology (12.5)]. If the patient’s CYP2C9 and/or VKORC1 genotype are known, consider these ranges in choosing the initial dose. Patients with CYP2C9 *1/*3, *2/*2, *2/*3, and *3/*3 may require more prolonged time (> 2 to 4 weeks) to achieve maximum INR effect for a given dosage regimen than patients without these CYP variants.
|†Ranges are derived from multiple published clinical studies. WKORC1 – 1639G>A (rs9923231) variant is used in this table. Other co-inherited VKORC1 variants may also be important determinants of warfarin dose.|
|GG||5-7 mg||5-7 mg||3-4 mg||3-4 mg||3-4 mg||0.5-2 mg|
|AG||5-7 mg||3-4 mg||3-4 mg||3-4 mg||0.5-2 mg||0.5-2 mg|
|AA||3-4 mg||3-4 mg||0.5-2 mg||0.5-2 mg||0.5-2 mg||0.5-2 mg|
Warfarin sodium is a narrow therapeutic range (index) drug, and its action may be affected by factors such as other drugs and dietary vitamin K. Therefore, anticoagulation must be carefully monitored during warfarin sodium therapy. Determine the INR daily after the administration of the initial dose until INR results stabilize in the therapeutic range. After stabilization, maintain dosing within the therapeutic range by performing periodic INRs. The frequency of performing INR should be based on the clinical situation but generally acceptable intervals for INR determinations are 1 to 4 weeks. Perform additional INR tests when other warfarin products are interchanged with warfarin sodium, as well as whenever other medications are initiated, discontinued, or taken irregularly. Heparin, a common concomitant drug, increases the INR [see Dosage and Administration (2.8) and Drug Interactions (7)].
Determinations of whole blood clotting and bleeding times are not effective measures for monitoring of warfarin sodium therapy.
The anticoagulant effect of warfarin sodium persists beyond 24 hours. If a patient misses a dose of warfarin sodium at the intended time of day, the patient should take the dose as soon as possible on the same day. The patient should not double the dose the next day to make up for a missed dose.
Some dental or surgical procedures may necessitate the interruption or change in the dose of warfarin sodium therapy. Consider the benefits and risks when discontinuing warfarin sodium even for a short period of time. Determine the INR immediately prior to any dental or surgical procedure. In patients undergoing minimally invasive procedures who must be anticoagulated prior to, during, or immediately following these procedures, adjusting the dosage of warfarin sodium to maintain the INR at the low end of the therapeutic range may safely allow for continued anticoagulation.
Since the full anticoagulant effect of warfarin sodium is not achieved for several days, heparin is preferred for initial rapid anticoagulation. During initial therapy with warfarin sodium, the interference with heparin anticoagulation is of minimal clinical significance. Conversion to warfarin sodium may begin concomitantly with heparin therapy or may be delayed 3 to 6 days. To ensure therapeutic anticoagulation, continue full dose heparin therapy and overlap warfarin sodium therapy with heparin for 4 to 5 days and until warfarin sodium has produced the desired therapeutic response as determined by INR, at which point heparin may be discontinued.
As heparin may affect the INR, patients receiving both heparin and warfarin sodium should have INR monitoring at least:
Warfarin sodium may increase the activated partial thromboplastin time (aPTT) test, even in the absence of heparin. A severe elevation (> 50 seconds) in aPTT with an INR in the desired range has been identified as an indication of increased risk of postoperative hemorrhage.
Consult the labeling of other anticoagulants for instructions on conversion to warfarin sodium.
Warfarin sodium tablets are contraindicated in women who are pregnant except in pregnant women with mechanical heart valves, who are at high risk of thromboembolism [see Warnings and Precautions (5.5) and Use in Specific Populations (8.1)]. Warfarin sodium tablets can cause fetal harm when administered to a pregnant woman. Warfarin sodium tablets exposure during pregnancy causes a recognized pattern of major congenital malformations (warfarin embryopathy and fetotoxicity), fatal fetal hemorrhage, and an increased risk of spontaneous abortion and fetal mortality. If warfarin sodium tablets are used during pregnancy or if the patient becomes pregnant while taking this drug, the patient should be apprised of the potential hazard to a fetus [see Warnings and Precautions (5.6) and Use in Specific Populations (8.1)].
− Active ulceration or overt bleeding of the gastrointestinal, genitourinary, or respiratory tract
− Central nervous system hemorrhage
− Cerebral aneurysms, dissecting aorta
− Pericarditis and pericardial effusions
− Bacterial endocarditis
Warfarin sodium can cause major or fatal bleeding. Bleeding is more likely to occur within the first month. Risk factors for bleeding include high intensity of anticoagulation (INR > 4.0), age greater than or equal to 65, history of highly variable INRs, history of gastrointestinal bleeding, hypertension, cerebrovascular disease, anemia, malignancy, trauma, renal impairment, certain genetic factors [see Clinical Pharmacology (12.5)], certain concomitant drugs [see Drug Interactions (7)], and long duration of warfarin therapy.
Perform regular monitoring of INR in all treated patients. Those at high risk of bleeding may benefit from more frequent INR monitoring, careful dose adjustment to desired INR, and a shortest duration of therapy appropriate for the clinical condition. However, maintenance of INR in the therapeutic range does not eliminate the risk of bleeding.
Drugs, dietary changes, and other factors affect INR levels achieved with warfarin sodium therapy. Perform more frequent INR monitoring when starting or stopping other drugs, including botanicals, or when changing dosages of other drugs [see Drug Interactions (7)].
Necrosis and/or gangrene of skin and other tissues is an uncommon but serious risk
(< 0.1%). Necrosis may be associated with local thrombosis and usually appears within a few days of the start of warfarin sodium therapy. In severe cases of necrosis, treatment through debridement or amputation of the affected tissue, limb, breast, or penis has been reported.
Careful clinical evaluation is required to determine whether necrosis is caused by an underlying disease. Although various treatments have been attempted, no treatment for necrosis has been considered uniformly effective. Discontinue warfarin sodium therapy if necrosis occurs. Consider alternative drugs if continued anticoagulation therapy is necessary.
Anticoagulation therapy with warfarin sodium may enhance the release of atheromatous plaque emboli. Systemic atheroemboli and cholesterol microemboli can present with a variety of signs and symptoms depending on the site of embolization. The most commonly involved visceral organs are the kidneys followed by the pancreas, spleen, and liver. Some cases have progressed to necrosis or death. A distinct syndrome resulting from microemboli to the feet is known as "purple toes syndrome." Discontinue warfarin sodium therapy if such phenomena are observed. Consider alternative drugs if continued anticoagulation therapy is necessary.
Do not use warfarin sodium as initial therapy in patients with heparin-induced thrombocytopenia (HIT) and with heparin-induced thrombocytopenia with thrombosis syndrome (HITTS). Cases of limb ischemia, necrosis, and gangrene have occurred in patients with HIT and HITTS when heparin treatment was discontinued and warfarin therapy was started or continued. In some patients, sequelae have included amputation of the involved area and/or death. Treatment with warfarin sodium may be considered after the platelet count has normalized.
Warfarin sodium can cause fetal harm when administered to a pregnant woman. While warfarin sodium is contraindicated during pregnancy, the potential benefits of using warfarin sodium may outweigh the risks for pregnant women with mechanical heart valves at high risk of thromboembolism. In those individual situations, the decision to initiate or continue warfarin sodium should be reviewed with the patient, taking into consideration the specific risks and benefits pertaining to the individual patient’s medical situation, as well as the most current medical guidelines. Warfarin sodium exposure during pregnancy causes a recognized pattern of major congenital malformations (warfarin embryopathy and fetotoxicity), fatal fetal hemorrhage, and an increased risk of spontaneous abortion and fetal mortality. If this drug is used during pregnancy, or if the patient becomes pregnant while taking this drug, the patient should be apprised of the potential hazard to a fetus [see Use in Specific Populations (8.1)].
Warfarin sodium exposure during pregnancy can cause pregnancy loss, birth defects, or fetal death. Discuss pregnancy planning with females of reproductive potential who are on warfarin sodium therapy [see Contraindications (4) and Use in Specific Populations (8.8)].
In the following clinical settings, the risks of warfarin sodium therapy may be increased:
The following factors may be responsible for increased INR response: diarrhea, hepatic disorders, poor nutritional state, steatorrhea, or vitamin K deficiency.
The following factors may be responsible for decreased INR response: increased vitamin K intake or hereditary warfarin resistance.
The following serious adverse reactions to warfarin sodium are discussed in greater detail in other sections of the labeling:
Other adverse reactions to warfarin sodium include:
Drugs may interact with warfarin sodium through pharmacodynamic or pharmacokinetic mechanisms. Pharmacodynamic mechanisms for drug interactions with warfarin sodium are synergism (impaired hemostasis, reduced clotting factor synthesis), competitive antagonism (vitamin K), and alteration of the physiologic control loop for vitamin K metabolism (hereditary resistance). Pharmacokinetic mechanisms for drug interactions with warfarin sodium are mainly enzyme induction, enzyme inhibition, and reduced plasma protein binding. It is important to note that some drugs may interact by more than one mechanism.
More frequent INR monitoring should be performed when starting or stopping other drugs, including botanicals, or when changing dosages of other drugs, including drugs intended for short-term use (e.g., antibiotics, antifungals, corticosteroids) [see Boxed Warning].
Consult the labeling of all concurrently used drugs to obtain further information about interactions with warfarin sodium or adverse reactions pertaining to bleeding.
CYP450 isozymes involved in the metabolism of warfarin include CYP2C9, 2C19, 2C8, 2C18, 1A2, and 3A4. The more potent warfarin S-enantiomer is metabolized by CYP2C9 while the R-enantiomer is metabolized by CYP1A2 and 3A4.
Examples of inhibitors and inducers of CYP2C9, 1A2, and 3A4 are below in Table 2; however, this list should not be considered all-inclusive. Consult the labeling of all concurrently used drugs to obtain further information about CYP450 interaction potential. The CYP450 inhibition and induction potential should be considered when starting, stopping, or changing dose of concomitant mediations. Closely monitor INR if a concomitant drug is a CYP2C9, 1A2, and/or 3A4 inhibitor or inducer.
|CYP2C9||amiodarone, capecitabine, cotrimoxazole, etravirine, fluconazole, fluvastatin, fluvoxamine, metronidazole, miconazole, oxandrolone, sulfinpyrazone, tigecycline, voriconazole, zafirlukast||aprepitant, bosentan, carbamazepine, phenobarbital, rifampin|
|CYP1A2||acyclovir, allopurinol, caffeine, cimetidine, ciprofloxacin, disulfiram, enoxacin, famotidine, fluvoxamine, methoxsalen, mexiletine, norfloxacin, oral contraceptives, phenylpropanolamine, propafenone, propranolol, terbinafine, thiabendazole, ticlopidine, verapamil, zileuton||montelukast,
omeprazole, phenobarbital, phenytoin,
|CYP3A4||alprazolam, amiodarone, amlodipine, amprenavir, aprepitant, atorvastatin, atazanavir, bicalutamide, cilostazol, cimetidine, ciprofloxacin, clarithromycin, conivaptan, cyclosporine, darunavir/ritonavir, diltiazem, erythromycin, fluconazole, fluoxetine, fluvoxamine, fosamprenavir, imatinib, indinavir, isoniazid, itraconazole, ketoconazole, lopinavir/ritonavir, nefazodone, nelfinavir, nilotinib, oral contraceptives, posaconazole, ranitidine, ranolazine, ritonavir, saquinavir, telithromycin, tipranavir, voriconazole, zileuton||armodafinil, amprenavir,
Examples of drugs known to increase the risk of bleeding are presented in Table 3. Because bleeding risk is increased when these drugs are used concomitantly with warfarin, closely monitor patients receiving any such drug with warfarin.
|Drug Class||Specific Drugs|
|Anticoagulants||argatroban, dabigatran, bivalirudin, desirudin,
|Antiplatelet Agents||aspirin, cilostazol, clopidogrel, dipyridamole,
|Nonsteroidal Anti-Inflammatory Agents||celecoxib, diclofenac, diflunisal, fenoprofen,
ibuprofen, indomethacin, ketoprofen,
ketorolac, mefenamic acid, naproxen,
oxaprozin, piroxicam, sulindac
|Serotonin Reuptake Inhibitors||citalopram, desvenlafaxine, duloxetine, escitalopram, fluoxetine, fluvoxamine, milnacipran, paroxetine, sertraline, venlafaxine, vilazodone.|
There have been reports of changes in INR in patients taking warfarin and antibiotics or antifungals, but clinical pharmacokinetic studies have not shown consistent effects of these agents on plasma concentrations of warfarin.
Closely monitor INR when starting or stopping any antibiotic or antifungal in patients taking warfarin.
Exercise caution when botanical (herbal) products are taken concomitantly with warfarin sodium. Few adequate, well-controlled studies evaluating the potential for metabolic and/or pharmacologic interactions between botanicals and warfarin sodium exist. Due to a lack of manufacturing standardization with botanical medicinal preparations, the amount of active ingredients may vary. This could further confound the ability to assess potential interactions and effects on anticoagulation.
Some botanicals may cause bleeding events when taken alone (e.g., garlic and Ginkgo biloba) and may have anticoagulant, antiplatelet, and/or fibrinolytic properties. These effects would be expected to be additive to the anticoagulant effects of warfarin sodium. Conversely, some botanicals may decrease the effects of warfarin sodium (e.g., co-enzyme Q10, St. John’s wort, ginseng). Some botanicals and foods can interact with warfarin sodium through CYP450 interactions (e.g., echinacea, grapefruit juice, ginkgo, goldenseal, St. John’s wort).
Monitor the patient’s response with additional INR determinations when initiating or discontinuing any botanicals.
Warfarin sodium tablets are contraindicated in women who are pregnant except in pregnant women with mechanical heart valves, who are at high risk of thromboembolism, and for whom the benefits of warfarin sodium may outweigh the risks. Warfarin sodium can cause fetal harm when administered to a pregnant woman. Warfarin sodium exposure during pregnancy causes a recognized pattern of major congenital malformations (warfarin embryopathy), fetal hemorrhage, and an increased risk of spontaneous abortion and fetal mortality. The reproductive and developmental effects of warfarin sodium have not been evaluated in animals. If this drug is used during pregnancy or if the patient becomes pregnant while taking this drug, the patient should be apprised of the potential hazard to the fetus.
In humans, warfarin crosses the placenta, and concentrations in fetal plasma approach the maternal values. Exposure to warfarin during the first trimester of pregnancy caused a pattern of congenital malformations in about 5% of exposed offspring. Warfarin embryopathy is characterized by nasal hypoplasia with or without stippled epiphyses (chondrodysplasia punctata) and growth retardation (including low birth weight). Central nervous system and eye abnormalities have also been reported, including dorsal midline dysplasia characterized by agenesis of the corpus callosum, Dandy-Walker malformation, midline cerebellar atrophy, and ventral midline dysplasia characterized by optic atrophy. Mental retardation, blindness, schizencephaly, microcephaly, hydrocephalus, and other adverse pregnancy outcomes have been reported following warfarin exposure during the second and third trimesters of pregnancy [see Contraindications (4) and Warnings and Precautions (5.6)].
Based on published data in 15 nursing mothers, warfarin was not detected in human milk. Among the 15 full-term newborns, 6 nursing infants had documented prothrombin times within the expected range. Prothrombin times were not obtained for the other 9 nursing infants. Monitor breast-feeding infants for bruising or bleeding. Effects in premature infants have not been evaluated. Caution should be exercised when warfarin sodium is administered to a nursing woman.
Adequate and well-controlled studies with warfarin sodium have not been conducted in any pediatric population, and the optimum dosing, safety, and efficacy in pediatric patients is unknown. Pediatric use of warfarin sodium is based on adult data and recommendations, and available limited pediatric data from observational studies and patient registries. Pediatric patients administered warfarin sodium should avoid any activity or sport that may result in traumatic injury.
The developing hemostatic system in infants and children results in a changing physiology of thrombosis and response to anticoagulants. Dosing of warfarin in the pediatric population varies by patient age, with infants generally having the highest, and adolescents having the lowest milligram per kilogram dose requirements to maintain target INRs. Because of changing warfarin requirements due to age, concomitant medications, diet, and existing medical condition, target INR ranges may be difficult to achieve and maintain in pediatric patients, and more frequent INR determinations are recommended. Bleeding rates varied by patient population and clinical care center in pediatric observational studies and patient registries.
Infants and children receiving vitamin K-supplemented nutrition, including infant formulas, may be resistant to warfarin therapy, while human milk-fed infants may be sensitive to warfarin therapy.
Of the total number of patients receiving warfarin sodium in controlled clinical trials for which data were available for analysis, 1885 patients (24.4%) were 65 years and older, while 185 patients (2.4%) were 75 years and older. No overall differences in effectiveness or safety were observed between these patients and younger patients, but greater sensitivity of some older individuals cannot be ruled out.
Patients 60 years or older appear to exhibit greater than expected INR response to the anticoagulant effects of warfarin [see Clinical Pharmacology (12.3)]. Warfarin sodium tablets are contraindicated in any unsupervised patient with senility. Observe caution with administration of warfarin sodium to elderly patients in any situation or with any physical condition where added risk of hemorrhage is present. Consider lower initiation and maintenance doses of warfarin sodium in elderly patients [see Dosage and Administration (2.2, 2.3)].
Renal clearance is considered to be a minor determinant of anticoagulant response to warfarin. No dosage adjustment is necessary for patients with renal impairment.
Hepatic impairment can potentiate the response to warfarin through impaired synthesis of clotting factors and decreased metabolism of warfarin. Use caution when using warfarin sodium in these patients.
Warfarin sodium exposure during pregnancy can cause spontaneous abortion, birth defects, or fetal death. Females of reproductive potential who are candidates for warfarin sodium therapy should be counseled regarding the benefits of therapy and potential reproductive risks. Discuss pregnancy planning with females of reproductive potential who are on warfarin sodium therapy. If the patient becomes pregnant while taking warfarin sodium, she should be apprised of the potential risks to the fetus.
Bleeding (e.g., appearance of blood in stools or urine, hematuria, excessive menstrual bleeding, melena, petechiae, excessive bruising or persistent oozing from superficial injuries, unexplained fall in hemoglobin) is a manifestation of excessive anticoagulation.
The treatment of excessive anticoagulation is based on the level of the INR, the presence or absence of bleeding, and clinical circumstances. Reversal of warfarin sodium anticoagulation may be obtained by discontinuing warfarin sodium therapy and, if necessary, by administration of oral or parenteral vitamin K1.
The use of vitamin K1 reduces response to subsequent warfarin sodium therapy and patients may return to a pretreatment thrombotic status following the rapid reversal of a prolonged INR. Resumption of warfarin sodium administration reverses the effect of vitamin K, and a therapeutic INR can again be obtained by careful dosage adjustment. If rapid re-anticoagulation is indicated, heparin may be preferable for initial therapy.
Prothrombin complex concentrate (PCC), fresh frozen plasma, or activated Factor VII treatment may be considered if the requirement to reverse the effects of warfarin sodium is urgent. A risk of hepatitis and other viral diseases is associated with the use of blood products; PCC and activated Factor VII are also associated with an increased risk of thrombosis. Therefore, these preparations should be used only in exceptional or life-threatening bleeding episodes secondary to warfarin sodium overdosage.
Warfarin sodium is an anticoagulant that acts by inhibiting vitamin K-dependent coagulation factors. Chemically, it is 3-(α- acetonylbenzyl)-4-hydroxycoumarin and is a racemic mixture of the R- and S-enantiomers. Crystalline warfarin sodium is an isopropanol clathrate. Its molecular formula is C19H15NaO4, and its structural formula is represented by the following:
Crystalline warfarin sodium occurs as a white, odorless, crystalline powder that is discolored by light. It is very soluble in water, freely soluble in alcohol, and very slightly soluble in chloroform and ether.
Each warfarin sodium tablet intended for oral administration contains warfarin sodium clathrates equivalent to 1 mg or 2 mg or 2.5 mg or 3 mg or 4 mg or 5 mg or 6 mg or 7.5 mg or 10 mg of warfarin sodium. In addition each tablet contains the inactive ingredients lactose monohydrate, starch, pregelatinised starch, hydroxypropyl cellulose, starlac and magnesium stearate. Additionally each 5 mg tablet contains: FD&C Yellow # 6 aluminum lake.
Warfarin acts by inhibiting the synthesis of vitamin K-dependent clotting factors, which include Factors II, VII, IX, and X, and the anticoagulant proteins C and S. Vitamin K is an essential cofactor for the post ribosomal synthesis of the vitamin K-dependent clotting factors. Vitamin K promotes the biosynthesis of γ -carboxyglutamic acid residues in the proteins that are essential for biological activity. Warfarin is thought to interfere with clotting factor synthesis by inhibition of the C1 subunit of vitamin K epoxide reductase (VKORC1) enzyme complex, thereby reducing the regeneration of vitamin K1 epoxide [see Clinical Pharmacology (12.5)].
An anticoagulation effect generally occurs within 24 hours after warfarin administration. However, peak anticoagulant effect may be delayed 72 to 96 hours. The duration of action of a single dose of racemic warfarin is 2 to 5 days. The effects of warfarin sodium may become more pronounced as effects of daily maintenance doses overlap. This is consistent with the half-lives of the affected vitamin K-dependent clotting factors and anticoagulation proteins: Factor II - 60 hours, VII - 4 to 6 hours, IX - 24 hours, X - 48 to 72 hours, and proteins C and S are approximately 8 hours and 30 hours, respectively.
Warfarin sodium is a racemic mixture of the R- and S-enantiomers of warfarin. The S-enantiomer exhibits 2 to 5 times more anticoagulant activity than the R-enantiomer in humans, but generally has a more rapid clearance.
Warfarin is essentially completely absorbed after oral administration, with peak concentration generally attained within the first four hours.
Warfarin distributes into a relatively small apparent volume of distribution of about 0.14 L/kg. A distribution phase lasting 6 to 12 hours is distinguishable after oral administration of an aqueous solution. Approximately 99% of the drug is bound to plasma proteins.
The elimination of warfarin is almost entirely by metabolism. Warfarin is stereoselectively metabolized by hepatic cytochrome P-450 (CYP450) microsomal enzymes to inactive hydroxylated metabolites (predominant route) and by reductases to reduced metabolites (warfarin alcohols) with minimal anticoagulant activity. Identified metabolites of warfarin include dehydrowarfarin, two diastereoisomer alcohols, and 4’-, 6-, 7-, 8-, and 10-hydroxywarfarin. The CYP450 isozymes involved in the metabolism of warfarin include CYP2C9, 2C19, 2C8, 2C18, 1A2, and 3A4. CYP2C9, a polymorphic enzyme, is likely to be the principal form of human liver CYP450 that modulates the in vivo anticoagulant activity of warfarin. Patients with one or more variant CYP2C9 alleles have decreased S-warfarin clearance [see Clinical Pharmacology (12.5)].
The terminal half-life of warfarin after a single dose is approximately one week; however, the effective half-life ranges from 20 to 60 hours, with a mean of about 40 hours. The clearance of R-warfarin is generally half that of S-warfarin, thus as the volumes of distribution are similar, the half-life of R-warfarin is longer than that of S-warfarin. The half-life of R-warfarin ranges from 37 to 89 hours, while that of S-warfarin ranges from 21 to 43 hours. Studies with radio labeled drug have demonstrated that up to 92% of the orally administered dose is recovered in urine. Very little warfarin is excreted unchanged in urine. Urinary excretion is in the form of metabolites.
Patients 60 years or older appear to exhibit greater than expected INR response to the anticoagulant effects of warfarin. The cause of the increased sensitivity to the anticoagulant effects of warfarin in this age group is unknown but may be due to a combination of pharmacokinetic and pharmacodynamic factors. Limited information suggests there is no difference in the clearance of S-warfarin; however, there may be a slight decrease in the clearance of R-warfarin in the elderly as compared to the young. Therefore, as patient age increases, a lower dose of warfarin is usually required to produce a therapeutic level of anticoagulation [see Dosage and Administration (2.3, 2.4)].
Asian patients may require lower initiation and maintenance doses of warfarin. A non-controlled study of 151 Chinese outpatients stabilized on warfarin for various indications reported a mean daily warfarin requirement of 3.3 ± 1.4 mg to achieve an INR of 2 to 2.5. Patient age was the most important determinant of warfarin requirement in these patients, with a progressively lower warfarin requirement with increasing age.
CYP2C9 and VKORC1 Polymorphisms
The S-enantiomer of warfarin is mainly metabolized to 7-hydroxywarfarin by CYP2C9, a polymorphic enzyme. The variant alleles, CYP2C9*2 and CYP2C9*3, result in decreased in vitro CYP2C9 enzymatic 7-hydroxylation of S-warfarin. The frequencies of these alleles in Caucasians are approximately 11% and 7% for CYP2C9*2 and CYP2C9*3, respectively.
Other CYP2C9 alleles associated with reduced enzymatic activity occur at lower frequencies, including *5, *6, and *11 alleles in populations of African ancestry and *5, *9, and *11 alleles in Caucasians.
Warfarin reduces the regeneration of vitamin K from vitamin K epoxide in the vitamin K cycle through inhibition of VKOR, a multiprotein enzyme complex. Certain single nucleotide polymorphisms in the VKORC1 gene (e.g., –1639G>A) have been associated with variable warfarin dose requirements. VKORC1 and CYP2C9 gene variants generally explain the largest proportion of known variability in warfarin dose requirements.
In five prospective, randomized, controlled clinical trials involving 3,711 patients with non-rheumatic AF, warfarin significantly reduced the risk of systemic thromboembolism including stroke (see Table 4). The risk reduction ranged from 60% to 86% in all except one trial (CAFA: 45%), which was stopped early due to published positive results from two of these trials. The incidence of major bleeding in these trials ranged from 0.6% to 2.7% (see Table 4).
|N||Thromboembolism||% Major Bleeding|
|Study||Warfarin- treated Patients||Control Patients||PT Ratio||INR||% Risk Reduction||p-value||Warfarin- treated Patients||Control Patients|
|*All study results of warfarin vs. control are based on intention-to=treat analysis and include ischemic stroke and systemic thromboembolism, excluding hemorrhagic stroke and transient ischemic attacks.|
In a prospective, randomized, open-label, positive-controlled study in 254 patients with mechanical prosthetic heart valves, the thromboembolic-free interval was found to be significantly greater in patients treated with warfarin alone compared with dipyridamole/aspirin-treated patients (p<0.005) and pentoxifylline/aspirin-treated patients (p<0.05). The results of this study are presented in Table 5.
|Patients Treated With|
|py = patient years|
|Thromboembolism||2.2/100 py||8.6/100 py||7.9/100 py|
|Major Bleeding||2.5/100 py||0.0/100 py||0.9/100 py|
In a prospective, open-label, clinical study comparing moderate (INR 2.65) vs. high intensity (INR 9.0) warfarin therapies in 258 patients with mechanical prosthetic heart valves, thromboembolism occurred with similar frequency in the two groups (4.0 and 3.7 events per 100 patient years, respectively). Major bleeding was more common in the high intensity group. The results of this study are presented in Table 6.
|Patients Treated With|
|Event||Moderate Warfarin Therapy
|High Intensity Warfarin Therapy
|py = patient years|
|Thromboembolism||4.0/100 py||3.7/100 py|
|Major Bleeding||0.95/100 py||2.1/100 py|
In a randomized trial in 210 patients comparing two intensities of warfarin therapy (INR 2.0 to 2.25 vs. INR 2.5 to 4.0) for a three month period following tissue heart valve replacement, thromboembolism occurred with similar frequency in the two groups (major embolic events 2.0 % vs. 1.9 %, respectively, and minor embolic events 10.8% vs. 10.2%, respectively). Major hemorrhages occurred in 4.6% of patients in the higher intensity INR group compared to zero in the lower intensity INR group.
WARIS (The Warfarin Re-Infarction Study) was a double-blind, randomized study of 1214 patients 2 to 4 weeks post-infarction treated with warfarin to a target INR of 2.8 to 4.8. The primary endpoint was a composite of total mortality and recurrent infarction. A secondary endpoint of cerebrovascular events was assessed. Mean follow-up of the patients was 37 months. The results for each endpoint separately, including an analysis of vascular death, are provided in Table 7:
|RR (95% CI)||% Risk Reduction
|RR= Relative risk; Risk reduction=(1 – RR); CI=Confidence interval; MI=Myocardial infarction; py=patient years|
|Total Patient Years of Follow-Up||2018||1944|
|Total Mortality||94 (4.7/100 py)||123 (6.3/100 py)||0.76 (0.60, 0.97)||24 (p=0.030)|
|Vascular Death||82 (4.1/100 py)||105 (5.4/100 py)||0.78 (0.60, 1.02)||22 (p=0.068)|
|Recurrent MI||82 (4.1/100 py)||124 (6.4/100 py)||0.66 (0.51, 0.85)||34 (p=0.001)|
|Cerebrovascular Event||20 (1.0/100 py)||44 (2.3/100 py)||0.46 (0.28, 0.75)||54 (p=0.002)|
WARIS II (The Warfarin, Aspirin, Re-Infarction Study) was an open-label, randomized study of 3630 patients hospitalized for acute myocardial infarction treated with warfarin to a target INR 2.8 to 4.2, aspirin 160 mg per day, or warfarin to a target INR 2.0 to 2.5 plus aspirin 75 mg per day prior to hospital discharge. The primary endpoint was a composite of death, nonfatal reinfarction, or thromboembolic stroke. The mean duration of observation was approximately 4 years. The results for WARIS II are provided in the Table 8.
|Aspirin plus Warfarin
|No. of Events|
|a Major bleeding episodes were defined as nonfatal cerebral hemorrhage or bleeding necessitating surgical intervention or blood transfusion.|
|b The rate ratio is for aspirin plus warfarin as compared with aspirin.|
|c The rate ratio is for warfarin as compared with aspirin.|
|d Minor bleeding episodes were defined as non-cerebral hemorrhage not necessitating surgical intervention or blood transfusion.|
|e Includes death, nonfatal reinfarction, and thromboembolic cerebral stroke|
|CI = confidence interval|
|ND = not detemined|
|Major Bleeding a||8||33||28||3.35 b (ND)||ND|
|4.00 c (ND)||ND|
|Minor Bleeding d||39||103||133||3.21 b (ND)||ND|
|2.55 c (ND)||ND|
|Composite Endpoints e||241||203||181||0.81 (0.69-0.95) b||0.03|
|0.71 (0.60-0.83) c||0.001|
|Reinfarction||117||90||69||0.56 (0.41-0.78) b||<0.001|
|0.74 (0.55-0.98) c||0.03|
|32||17||17||0.52 (0.28-0.98) b||0.03|
|0.52 (0.28-0.97) c||0.03|
There were approximately four times as many major bleeding episodes in the two groups receiving warfarin than in the group receiving aspirin alone. Major bleeding episodes were not more frequent among patients receiving aspirin plus warfarin than among those receiving warfarin alone, but the incidence of minor bleeding episodes was higher in the combined therapy group.
Warfarin sodium tablets, USP are supplied as follows:
5 mg Tablets: Peach, Round, Flat Beveled edge tablets de-bossed ‘I’ on the left side of bisect and ‘G’ on the right side of bisect on one side and ‘332’ on other, supplied in bottles of 30’s count NDC 58517-360-30.
Storage: Store at 20° to 25°C (68° F to 77° F). [See USP Controlled Room Temperature]. Protect from light. Dispense in a tight, light-resistant container as defined in the USP.
See FDA-approved patient labeling (Medication Guide).
Advise patients to:
− immediately if they think they are pregnant
− to discuss pregnancy planning
− if they are considering breast-feeding
Warfarin Sodium Tablets, USP
Read this Medication Guide before you start taking warfarin sodium and each time you get a refill. There may be new information. This Medication Guide does not take the place of talking to your healthcare provider about your medical condition or treatment. You and your healthcare provider should talk about warfarin sodium when you start taking it and at regular checkups.
Warfarin sodium can cause bleeding which can be serious and sometimes lead to death. This is because warfarin sodium is a blood thinner medicine that lowers the chance of blood clots forming in your body.
Tell your healthcare provider if you take any of these medicines. Ask your healthcare provider if you are not sure if your medicine is one listed above.
Many other medicines can interact with warfarin sodium and affect the dose you need or increase warfarin sodium side effects. Do not change or stop any of your medicines or start any new medicines before you talk to your healthcare provider.
Do not take other medicines that contain warfarin sodium while taking warfarin sodium.
See "What are the possible side effects of warfarin sodium?" for more information about side effects.
What is warfarin sodium?
Warfarin sodium is prescription medicine used to treat blood clots and to lower the chance of blood clots forming in your body. Blood clots can cause a stroke, heart attack, or other serious conditions if they form in the legs or lungs. It is not known if warfarin sodium is safe and effective in children.
Do not take warfarin sodium if:
What should I tell my healthcare provider before taking warfarin sodium?
Before you take warfarin sodium, tell your healthcare provider if you:
Tell all of your healthcare providers and dentists that you are taking warfarin sodium. They should talk to the healthcare provider who prescribed warfarin sodium for you before you have any surgery or dental procedure. Your warfarin sodium may need to be stopped for a short time or your may need your dose adjusted.
Tell your healthcare provider about all the medicines you take, including prescription and non-prescription medicines, vitamins, and herbal supplements. Some of your other medicines may affect the way warfarin sodium works. Certain medicines may increase your risk of bleeding. See "What is the most important information I should know about warfarin sodium?"
Know the medicines you take. Keep a list of them to show your healthcare provider and pharmacist when you get a new medicine.
How should I take warfarin sodium?
What should I avoid while taking warfarin sodium?
What are the possible side effects of warfarin sodium?
Warfarin sodium may cause serious side effects including:
Tell your healthcare provider if you have any side effect that bothers you or does not go away.
These are not all of the side effects of warfarin sodium. For more information, ask your healthcare provider or pharmacist.
Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.
How should I store warfarin sodium?
Keep warfarin sodium and all medicines out of the reach of children.
General information about warfarin sodium.
Medicines are sometimes prescribed for purposes other than those listed in a Medication Guide. Do not use warfarin sodium for a condition for which it was not prescribed. Do not give warfarin sodium to other people, even if they have the same symptoms that you have. It may harm them.
This Medication Guide summarizes the most important information about warfarin sodium. If you would like more information, talk with your healthcare provider. You can ask your healthcare provider or pharmacist for information about warfarin sodium that is written for healthcare professionals.
If you would like more information, talk to your healthcare provider or call New Horizon Rx Group, LLC toll free at 1-855-465-5545.
What are the ingredients in warfarin sodium, USP?
Active ingredient: Warfarin Sodium, USP
Inactive ingredients: Each warfarin sodium tablet intended for oral administration contains warfarin sodium clathrates equivalent to 5 mg of warfarin sodium.
In addition each tablet contains the inactive ingredients lactose monohydrate, pregelatinized starch, hydroxypropyl cellulose, and magnesium stearate. Additionally each 5 mg tablet contains: FD&C Yellow # 6 aluminum lake.
This Medication Guide has been approved by the U.S. Food and Drug Administration.
New Horizon Rx Group, LLC
Kenner, LA 70062
Cadila Healthcare Ltd.
warfarin sodium tablet
|Labeler - New Horizon Rx Group, LLC (056256127)|
|Registrant - New Horizon Rx Group, LLC (056256127)|
|Cadila Healthcare Ltd.||918596198||MANUFACTURE(58517-360)|