protocol for warfarin anticoagulation

Dosage: Initiation of warfarin daily dose of warfarin (mg) day INR mg (< 80 kg) mg (> 80 kg) 1 < 1.5 5 7.5 - > 1.5 off protocol off protocol 2 < 1.5 5 7.5 - 1.5-1.9 2.5 5-7.5 - 2.0-2.5 0-.2.5 0-5 - > 2.5 0 0 3 < 1.5 5-10 7.5 - 1.5-1.9 2.5-5 5-10 - 2.0-3.0 0-2.5 0-5 - > 3.0 0 0 4 < 1.5 10 12.5-15 - 1.5-1.9 5-7.5 5-10 - 2.0-3.0 0-5 0-5 - > 3.0 0 0-2.5 5 < 1.5 10 10-15 - 1.5-1.9 5-7.5 5-10 - 2.0-3.0 0-5 0-5 - > 3.0 0 0 6 < 1.5 7.5-12.5 15 - 1.5-1.9 5-10 5-12.5 - 2.0-3.0 0-7.5 0-7.5 - > 3.0 0 0-5 - For patient beginning warfarin therapy, INR testing should be done every daily for 1 week, then weekly until stable for 2 consecutive tests, every 2 weeks until stable for 2 consecutive tests, then every 3-4 weeks - Every 12 weeks may be sufficient [4] Management: - Maintenance of warfarin - Weekly dosage change for target INR Current INR 1.5-2.0 2.0-3.0 2.5-3.0 < 1.5 i* 5-10% i* 5-20% i* 5-20% - (2 weeks) (2 weeks) (2 weeks) 1.5-2.0 - i* 5-10% i* 5-15% - (4 weeks) (2 weeks) (2 weeks) 2.0-2.5 d* 5-10% - i* 5-10% - (2 weeks) (4 weeks) (2 weeks) 2.5-3.0 d* 5-15% - - - (2 weeks) (4 weeks) (4 weeks) 3.0-3.5 d* 10-20%, d* 5-10% - - may hold dose (2 weeks) (4 weeks) - (2 weeks) - - 3.5-4.0 hold dose d* 5-10% d* 5-10% - d* 20-50% may hold dose (2 weeks) - (2 weeks) (2 weeks) - 4.0-6.0 hold 2-3 days hold 1-2 days may hold 1-2 days - d* 20-50% d* 10-20% d* 5-10% - (2 weeks) (2 weeks) (2 weeks) 6.0-9.0 hold warfarin, consider admission to hospital - - > 9 hold warfarin, consider admission to hospital, administration of vitamin K* - - i* increase dosage d* decrease dosage # retest INR within time specified * vitamin K 2.5-5.0 mg PO if no significant bleeding; vitamin K 10 mg IV infusion if significant bleeding regardless of INR (if elevated) [5] * for serious bleeding, also administer fresh frozen plasma, prothrombin complex concentrate or recombinant factor VII in addition to vitamin K - Solitary deviations in INR with a history of stable control may be retested within 2 weeks with a slight decrease in dosage for 1 day only, and only in the absence of an identifiable trend change. - Identification & control of precipitating factors (i.e. change in diet, disease state, drugs) is necessary to achieve stable anticoagulation & if remediable may make a warfarin dosage change unnecessary. - Statistical modeling suggests that, for optimal management of target INR of 2.0-3.0, warfarin dose should be changed when INRs are =< 1.7 or >= 3.3 [3] - Older age & amiodarone use predictive of lower doses to achieve therapeutic levels. [2]

General

pharmacology protocol

References

West LA Veterans Administration pharmacy, 2004
Journal Watch 25(15):117, 2005 Garcia D, Regan S, Crowther M, Hughes RA, Hylek EM. Warfarin maintenance dosing patterns in clinical practice: implications for safer anticoagulation in the elderly population. Chest. 2005 Jun;127(6):2049-56. PMID: 15947319
Rose AJ et al Warfarin dose management affects INR control. J Thromb Haemost 2009 Jan; 7:94. PMID: 18983486
Schulman S et al. Warfarin dose assessment every 4 weeks versus every 12 weeks in patients with stable international normalized ratios: A randomized trial. Ann Intern Med 2011 Nov 15; 155:653 PMID: 22084331
Geriatrics at your Fingertips, 13th edition, 2011 Reuben DB et al (eds) American Geriatric Society

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