Evaluation of Maintenance Dosing vs Loading Dosing Upon Restarting Warfarin Therapy: A Prospective Randomized Trial

Overview

A prospective, randomized trial to compare the time taken to achieve a therapeutic INR upon re-starting warfarin at a "loading" dose (namely 1.5 times the "maintenance" dose for 3 days) compared to the known "maintenance" dose.

Full Title of Study: “Evaluation of Maintenance Dosing vs Loading Dosing Upon Restarting Warfarin Therapy: A Prospective Randomized Trial.”

Study Type

  • Study Type: Interventional
  • Study Design
    • Allocation: Randomized
    • Intervention Model: Parallel Assignment
    • Primary Purpose: Treatment
    • Masking: None (Open Label)
  • Study Primary Completion Date: August 2012

Detailed Description

Patients will be identified via the University of Alberta Hospital Anticoagulation Management Service. Following the receipt of written, informed consent, patients will be randomized to re-start warfarin at their "maintenance" dose or at a "loading" dose (1.5 times the maintenance dose for 3 days, then resumption of warfarin dosing as per the maintenance dose). Randomization will be performed on-line through the EPICORE Centre.

Assuming Day 1 is the day warfarin is re-started, patients will have INRs done on day 3 and at least every 2 days thereafter until a therapeutic INR is obtained. In addition, protein C, protein S and factor II levels will be obtained while the patient is on stable maintenance dosing of warfarin (i.e., prior to holding warfarin for the procedure), 7 days after re-starting warfarin, and 14 days after re-starting warfarin. Complete blood counts (CBCs) will be done with each INR if the patient is taking a low molecular weight heparin (LMWH). Patients will have their anticoagulant therapy managed by the AMS for 6 weeks and will receive a telephone follow-up by the AMS at 90 days to determine if any bleeding or clotting complications occurred.

Interventions

  • Drug: warfarin
    • Patients will be randomized to re-start warfarin at their “maintenance” dose or at a “loading” dose (1.5 times the maintenance dose for 3 days, then resumption of warfarin dosing as per the maintenance dose).
  • Drug: Warfarin
    • “Maintenance” dose is the amount of warfarin that a patient required to maintain a therapeutic INR.

Arms, Groups and Cohorts

  • Experimental: Loading
    • 1.5 times the maintenance dose for 3 days, then resumption of warfarin dosing as per the maintenance dose
  • Active Comparator: Maintenance
    • Re-start same dose as previously stable on

Clinical Trial Outcome Measures

Primary Measures

  • re-starting warfarin “loading” dose vs “maintenance” dose
    • Time Frame: INR drawn 3 days post-reinitiation and then every 2 days until therapeutic
    • To compare the time taken to achieve a therapeutic INR between those patients re-starting warfarin with a “loading” dose and a “maintenance” dosing regimen using linear interpolation of INRs.

Secondary Measures

  • Compare % of time within, above and below the target INR range
    • Time Frame: days
    • To compare the % of time within, above and below the desired INR range between those patients re-starting warfarin with a “loading” dose or “maintenance” dose 6 weeks following restarting warfarin.
  • Compare bleeding/clotting complications between two groups
    • Time Frame: 30 days, 90 days
    • To compare the rates of thrombosis (i.e., stroke) / major hemorrhage between those re-starting warfarin with a “loading” dose or “maintenance” dose at 30 days and 90 days following restarting warfarin.
  • Compare the levels of protein C, protein S, and factor II between 2 groups.
    • Time Frame: week
    • To compare the levels of protein C, protein S, and factor II between those re-starting warfarin with a “loading” dose or “maintenance” dose.

Participating in This Clinical Trial

Inclusion Criteria

  • Have 'stable warfarin maintenance dosing' (defined as last 2 INRs within therapeutic range with weekly warfarin dosing not being changed any more than 10%)
  • Have an INR indicative of not taking any warfarin (INR <1.4) or confirmation of the patient not taking any warfarin in the past 4 days
  • Provide written, informed consent

Gender Eligibility: All

Minimum Age: 18 Years

Maximum Age: N/A

Are Healthy Volunteers Accepted: No

Investigator Details

  • Lead Sponsor
    • University of Alberta
  • Provider of Information About this Clinical Study
    • Principal Investigator: Tammy Bungard, Principal Investigator – University of Alberta
  • Overall Official(s)
    • Tammy J Bungard, BSP, PharmD, Principal Investigator, Univeristy of Alberta
    • Bruce Ritchie, MD, FRCPC, Principal Investigator, University of Alberta

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