General High Alert Medication: This medication bears a heightened risk of causing significant patient harm when it is used in error. Genetic Implications: Pronunciation:
Trade Name(s) Ther.
Class. anticoagulants Pharm. Class. coumarins Indications
Action Interferes with hepatic synthesis of vitamin K-dependent clotting factors (II, VII, IX, and X). Therapeutic Effect(s): Prevention of thromboembolic events. PharmacokineticsAbsorption: Well absorbed from the GI tract after oral administration. Distribution: Crosses the placenta but does not enter breast milk. Protein Binding: 99%. Metabolism and Excretion: Primarily metabolized by the liver via the CYP2C9 isoenzyme, with some metabolism via the CYP3A4 isoenzyme; the CYP2C9 isoenzyme exhibits genetic polymorphism (intermediate or poor metabolizers may have significantly ↑ (S)-warfarin concentrations and an ↑ risk of adverse reactions). Half-life: 42 hr. TIME/ACTION PROFILE (effects on coagulation tests)
Contraindication/PrecautionsContraindicated in:
Use Cautiously in:
Adverse Reactions/Side EffectsDerm: dermal necrosis GI: cramps, nausea GU: CALCIPHYLAXIS Hemat: BLEEDING Misc: fever * CAPITALS indicate life-threatening. InteractionsDrug-Drug
Drug-Natural Products:
Drug-Food: Ingestion of large quantities of foods high in vitamin K content (see list in food sources for specific nutrients) may antagonize the anticoagulant effect of warfarin. Route/DosagePO (Adults): 2–5 mg/day for 2–4 days; then adjust daily dose by results of INR. Initiate therapy with lower doses in geriatric or debilitated patients or in Asian patients or those with CYP2C9*2 and/or CYP2C9*3 alleles or VKORC1 AA genotype. PO (Children >1 mo): Initial loading dose– 0.2 mg/kg (maximum dose: 10 mg) for 2–4 days then adjust daily dose by results of INR, use 0.1 mg/kg if liver dysfunction is present. Maintenance dose range– 0.05–0.34 mg/kg/day. Availability (generic available)Tablets: 1 mg, 2 mg, 2.5 mg, 3 mg, 4 mg, 5 mg, 6 mg, 7.5 mg, 10 mg Cost: Generic: 1 mg $10.83/100, 2 mg $10.83/100, 2.5 mg $10.83/100, 3 mg $10.83/100, 4 mg $10.83/100, 5 mg $8.52/100, 6 mg $10.64/100, 7.5 mg $10.83/100, 10 mg $10.83/100 Assessment (adsbygoogle = window.adsbygoogle || []).push({});
Lab Test Considerations: Monitor PT, INR, and other clotting factors frequently during therapy; monitor more frequently in patients with renal impairment. Therapeutic PT ranges 1.3–1.5 times greater than control; however, the INR, a standardized system that provides a common basis for communicating and interpreting PT results, is usually referenced. Normal INR (not on anticoagulants) is 0.8–1.2. An INR of 2.5–3.5 is recommended for patients at very high risk of embolization (for example, patients with mitral valve replacement and ventricular hypertrophy). Lower levels are acceptable when risk is lower. Heparin may affect the PT/INR; draw blood for PT/INR in patients receiving both heparin and warfarin at least 5 hr after the IV bolus dose, 4 hr after cessation of IV infusion, or 24 hr after subcut heparin injection. Asian patients and those who carry the CYP2C9*2 allele and/or the CYP2C9*3 allele, or those with VKORC1 AA genotype may require more frequent monitoring and lower doses.
Toxicity and Overdose: Withholding 1 or more doses of warfarin is usually sufficient if INR is excessively elevated or if minor bleeding occurs. If overdose occurs or anticoagulation needs to be immediately reversed, the antidote is vitamin K (phytonadione, Aquamephyton). Administration of whole blood or plasma also may be required in severe bleeding because of the delayed onset of vitamin K. Implementation
Patient/Family Teaching
Evaluation/Desired OutcomesProlonged PT (1.3–2.0 times the control; may vary with indication) or INR of 2–4.5 without signs of hemorrhage. warfarin is a sample topic from the Davis's Drug Guide. To view other topics, please log in or purchase a subscription. Nursing Central is an award-winning, complete mobile solution for nurses and students. Look up information on diseases, tests, and procedures; then consult the database with 5,000+ drugs or refer to 65,000+ dictionary terms. Complete Product Information. What precautions should the nurse take when obtaining the blood specimen for testing?To prevent hemolysis (which can interfere with many tests):
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