Chest
Volume 119, Issue 1, Supplement, January 2001, Pages 22S-38S
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Managing Oral Anticoagulant Therapy

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Initiation and Maintenance Dosing

Following the administration of warfarin, an observableanticoagulant effect occurs within 2 to 7 days, depending onthe dose administered.20, 21 When a rapid effect isrequired, heparin should be given concurrently with warfarin for atleast 4 days. The common practice of initiating warfarin therapy with aloading dose is unnecessary in most patients, and commencing with anaverage maintenance dose of 5 mg warfarin usually results in an INR of2.0 in 4 or 5 days.21 Heparin treatment is

Management of Nontherapeutic INRs

Some patients receiving long-term warfarin therapy are difficultto manage because they have unexpected fluctuations in doseresponse.28 These unexpected fluctuations could be due toa number of variables, including inaccuracy in PT testing, changes invitamin K1 intake (ie, increased ordecreased vitamin K1 in the diet), changes invitamin K1 or warfarin absorption (eg, GI factors or drug effects), changes in warfarin metabolism(eg, liver disease or drug effects), changes in vitaminK1-dependent

Management of Oral Anticoagulation During Invasive Procedures

Clinicians often are required to assess the risk of bleeding froma procedure if anticoagulation therapy is continued vs the risk ofthrombosis if anticoagulation therapy is discontinued, as well as thecost of alternative anticoagulation options. This subject has beenreviewed with suggested alternative options based on an estimate of thepreoperative and postoperative daily risk of bleeding orthrombosis.40 With each of the following options, the length of time for warfarin dosage reduction and for

Definition of Major and Minor Hemorrhage

Precise estimates of hemorrhagic event rates are complicated bythe inconsistency between classification schemes in clinical researchstudies.12 The goal of classification is to place ableeding episode on a continuum of severity ranging from minor events, such as brief epistaxis that would not have been reported to aphysician (but would, for example, be recorded as part of a clinicaltrial), to a fatal or life-threatening episode of bleeding. Fihn etal12 established the following three categories:

Management of the Patient Who Bleeds During Warfarin Therapy

The short-term management of patients who bleed with anexcessively prolonged INR has been discussed above. The long-termmanagement of patients who bleed but who require ongoing protectionagainst systemic embolism (eg, patients with mechanicalheart valves or with atrial fibrillation and other risk factors) isproblematic. There are two general principles that should be followed:(1) to attempt to identify and reverse the cause of bleeding; and (2)to examine the possibility of lowering the

Models of Anticoagulation Management

The effectiveness and safety of warfarin are critically dependenton maintaining the INR in the therapeutic range. This objective isfacilitated by aiming for an INR that is in the middle of the INR range(ie, a goal of 2.5 for a designated range of 2.0 to 3.0, anda goal of 3.0 for a designated range of 2.5 to 3.5). The impact ofmaintaining good anticoagulant control was highlighted by reanalysis ofthe primary prevention trials in atrial fibrillation using anon-treatment analysis.1 The results of

Pregnancy

Oral anticoagulants cross the placenta and can produce acharacteristic embryopathy, CNS abnormalities, fetal bleeding, orincreased rates of fetal death.152, 153 These complications are discussed in detail elsewhere in this supplement (see page 122). The incidence of warfarin embryopathy is greatest during 6to 12 weeks' gestation, and warfarin should be avoided during thisperiod of pregnancy.152 Since CNS abnormalities, fetalbleeding, and fetal death may occur throughout pregnancy,

Practical Dosing

  • 1.

    For the initiation of and maintenance dosing of warfarin, commence therapy with an average maintenance dose of 5 mg (grade 2Acompared to a dose of 10 mg). Starting doses of < 5 mg might beappropriate for elderly patients, patients with impaired nutrition orliver disease, and in patients with a high risk for bleeding.

Management of Nontherapeutic INRs

  • 1.

    For patients with INRs greater than the therapeutic levelbut < 5.0 who do not have significant bleeding, lower the dose oromit a dose and resume therapy at a lower dose when the INR

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