Pregnancy Risk Category X
How supplied
Tablets: 1 mg, 2 mg, 2.5 mg, 3 mg, 4 mg, 5 mg, 6 mg, 7.5 mg, 10 mg
Injection: 2 mg/ml (powder)
Action
Inhibits vitamin K-dependent activation of clotting factors II, VII, IX, and X, formed in the liver.
Indications & dosage
Pulmonary embolism associated with deep vein thrombosis, MI, rheumatic heart disease with heart valve damage, prosthetic heart valves, chronic atrial fibrillation--
Adults: 2 to 5 mg P.O. daily for 2 to 4 days; then dosage based on daily PT and INR. Usual maintenance dose is 2 to 10 mg P.O. daily; I.V. dosage would be same as that used P.O.
Adverse reactions
GI: anorexia, nausea, vomiting, cramps, diarrhea, mouth ulcerations, sore mouth, melena.
GU: hematuria, excessive menstrual bleeding.
Hematologic: hemorrhage; prolonged PT, INR, and PTT.
Hepatic: hepatitis, elevated liver function test results, jaundice.
Skin: dermatitis, urticaria, necrosis, gangrene, alopecia, rash.
Other: fever, headache; enhanced uric acid excretion.
Interactions
Drug-drug. Acetaminophen: may increase bleeding with long-term therapy (more than 2 weeks) with high doses (more than 2 g/day) of acetaminophen. Monitor very carefully.
Allopurinol, amiodarone, anabolic steroids, cephalosporins, chloramphenicol, cimetidine, ciprofloxacin, clofibrate, danazol, diazoxide, diflunisal, disulfiram, erythromycin, ethacrynic acid, fenoprofen calcium, fluconazole, fluoroquinolones, glucagon, heparin, ibuprofen, influenza virus vaccine, isoniazid, itraconazole, ketoprofen, lovastatin, meclofenamate,
methimazole, methylthiouracil, metronidazole, miconazole, nalidixic acid, neomycin (oral), norfloxacin, ofloxacin, omeprazole, pentoxifylline, propafenone, propoxyphene, propylthiouracil, quinidine, simvastatin, streptokinase, sulfinpyrazone, sulfonamides, sulindac, tamoxifen, tetracyclines, thiazides, thyroid drugs, tricyclic antidepressants, urokinase, vitamin E: increased PT and INR. Monitor patient carefully for bleeding. Consider anticoagulant dosage reduction.
Anticonvulsants: increased serum levels of phenytoin and phenobarbital. Monitor closely.
Barbiturates, carbamazepine, corticosteroids, corticotropin, dicloxacillin, ethchlorvynol, griseofulvin, haloperidol, meprobamate, mercaptopurine, methaqualone, nafcillin, oral contraceptives containing estrogen, rifampin, spironolactone, sucralfate, trazodone: decreased PT and INR with reduced anticoagulant effect. Monitor patient carefully.
Chloral hydrate, glutethimide, propylthiouracil, sulfinpyrazone: increased or decreased PT. Avoid use, if possible, and monitor patient carefully.
Cholestyramine: decreased response when administered too closely together. Administer 6 hours after oral anticoagulants.
NSAIDs, salicylates: increased PT and INR; ulcerogenic effects. Don't use together.
Sulfonylureas (oral antidiabetics): increased hypoglycemic response. Monitor blood glucose levels.
Drug-food. Foods or enteral products containing vitamin K: may impair anticoagulation. Patient should maintain consistent daily intake of leafy green vegetables.
Drug-herb. Angelica: significantly prolonged PT when Angelica sinensis is given with warfarin. Avoid concomitant use.
Motherwort, red clover: risk of increased bleeding. Avoid concomitant use.
Drug-lifestyle. Alcohol use: enhanced anticoagulant effects may occur. Tell patient to avoid large amounts of alcohol.
Effects on diagnostic tests
Warfarin can cause false-negative serum theophylline levels.
Contraindications
Contraindicated in patients with hypersensitivity to drug and in those with bleeding from the GI, GU, or respiratory tracts; aneurysm; cerebrovascular hemorrhage; severe or malignant hypertension; severe renal or hepatic disease; subacute bacterial endocarditis, pericarditis, or pericardial effusion; or blood dyscrasias or hemorrhagic tendencies. Also contraindicated during pregnancy, threatened abortion, eclampsia, or preeclampsia and after recent surgery involving large open areas, eye, brain, or spinal cord; recent prostatectomy; major regional lumbar block anesthesia, spinal puncture, or diagnostic or therapeutic invasive procedures.
Don't use in patients with a history of warfarin-induced necrosis; in unsupervised patients with senility, alcoholism, or psychosis; or in situations in which there are inadequate laboratory facilities for coagulation testing.
Nursing considerations
I.V. administration
Patient teaching
*Liquid contains alcohol. **May contain tartrazine. †Canada ‡Australia §U.K. OTCOver the counter
Reactions may be common, uncommon, life-threatening, or COMMON AND LIFE-THREATENING