title: Management and dosing of warfarin therapy.
abstract: When initiating warfarin therapy, clinicians should avoid loading doses that can raise the International Normalized Ratio (INR) excessively; instead, warfarin should be initiated with a 5-mg dose (or 2 to 4 mg in the very elderly). With a 5-mg initial dose, the INR will not rise appreciably in the first 24 hours, except in rare patients who will ultimately require a very small daily dose (0.5 to 2.0 mg). Adjusting a steady-state warfarin dose depends on the measured INR values and clinical factors: the dose does not need to be adjusted for a single INR that is slightly out of range, and most changes should alter the total weekly dose by 5% to 20%. The INR should be monitored frequently (eg, 2 to 4 times per week) immediately after initiation of warfarin; subsequently, the interval between INR tests can be lengthened gradually (up to a maximum of 4 to 6 weeks) in patients with stable INR values. Patients who have an elevated INR will need more frequent testing and may also require vitamin K1. For example, a nonbleeding patient with an INR of 9 can be given low-dose vitamin K1 (eg, 2.5 mg phytonadione, by mouth). Patients who have an excessive INR with clinically important bleeding require clotting factors (eg, fresh-frozen plasma) as well as vitamin K1.
authors.affiliation: Division of General Medical Science (BFG), Washington University School of Medicine, St. Louis, Missouri, USA.
authors.forename: B F
authors.initials: BF
authors.lastname: Gage
authors.forename: S D
authors.initials: SD
authors.lastname: Fihn
authors.forename: R H
authors.initials: RH
authors.lastname: White
mesh_terms: D000284:Administration, Oral; D000925:Anticoagulants / Q000008:administration & dosage* / Q000009:adverse effects / Q000097:blood / Q000494:pharmacology*; D004334:Drug Administration Schedule; D016903:Drug Monitoring; D006470:Hemorrhage / Q000139:chemically induced / Q000517:prevention & control*; D006801:Humans; D019934:International Normalized Ratio; D018670:Monitoring, Ambulatory; D014859:Warfarin / Q000008:administration & dosage* / Q000009:adverse effects / Q000097:blood / Q000494:pharmacology*
chemical_list: D000925:Anticoagulants; D014859:Warfarin