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Low Dose Supplementation to Improve Anticoagulation Control With Oral Vitamin K as an Adjuvant to Warfarin Therapy (LOCK)

This study has been completed.
Information provided by:
Ottawa Hospital Research Institute Identifier:
First received: November 18, 2008
Last updated: July 26, 2011
Last verified: July 2011
The main objective of this study is to assess the effectiveness of low dose Vitamin K1 (200 micrograms per day) at improving anticoagulation control in unstable patients on warfarin. This study will also aim to look at effectiveness in the context of genes known to influence warfarin metabolism, variability in the consumption of Vitamin K rich foods, and patient knowledge about warfarin anticoagulation -- factors which have been associated with anticoagulation control and which can influence the effectiveness of this intervention in clinical practice.

Condition Intervention Phase
Dietary Supplement: Vitamin K1 (Phytonadione)
Dietary Supplement: Placebo
Phase 3

Study Type: Interventional
Study Design: Allocation: Randomized
Intervention Model: Parallel Assignment
Masking: Double Blind (Participant, Investigator, Outcomes Assessor)
Primary Purpose: Treatment
Official Title: A Phase III Pilot RCT (Randomized, Controlled Trial) to Assess the Effectiveness of Low Dose Vitamin K1 (200 Micrograms Per Day) on Improving Anticoagulation Control in Unstable Patients on Warfarin

Resource links provided by NLM:

Further study details as provided by Ottawa Hospital Research Institute:

Primary Outcome Measures:
  • Anticoagulation control -- Point estimates (and standard deviations) for the following variables: Percent time in therapeutic range, standard deviation of INRs, number of INRs outside of therapeutic range, and number of dose changes [ Time Frame: At study initiation (for the six month pre-intervention period) and at study completion (after the six-month intervention period) ]
  • Recruitment Numbers -- Number of patients deemed eligible, Number of patients solicited, Number of patients screened, Number of patients enrolled, and Number of enrolled patients lost to follow-up [ Time Frame: Monthly ]

Secondary Outcome Measures:
  • Bleeding Events -- Both major and minor as defined by the International Society on Thrombosis and Haemostasis (ISTH) criteria [ Time Frame: Over 6 month study period ]
  • Recurrent thrombosis [ Time Frame: Over six month study period ]

Estimated Enrollment: 100
Study Start Date: November 2008
Study Completion Date: April 2010
Primary Completion Date: April 2010 (Final data collection date for primary outcome measure)
Arms Assigned Interventions
Active Comparator: Vitamin K Dietary Supplement: Vitamin K1 (Phytonadione)
Vitamin K1 tablets (100 micrograms per tablet) will be taken by patients randomized to the Vitamin K arm. Dosage is two tablets per day (200 micrograms per day) to be taken with warfarin for the 6 month study period.
Placebo Comparator: Placebo Dietary Supplement: Placebo
Lactose-based placebo tablets (identical in appearance to the Vitamin K1 tablets) will be taken by patients randomized to the placebo arm. Dosage is two tablets per day to be taken with warfarin for the 6 month study period.

Detailed Description:
A double-blinded placebo controlled pilot RCT assessing the effectiveness of daily supplementation with low dose Vitamin K1 (200 micrograms per day) against placebo at improving anticoagulation control. Previous studies assessing the efficacy of this intervention have been small and further trials are required to evaluate the true effectiveness and safety profile. Furthermore the impact of genetic polymorphisms, known to impact warfarin metabolism, on the effectiveness/safety of this intervention will also be assessed in this study. Demographic and clinical variables as well as potential confounding variables such as variable dietary Vitamin K intake, concomitant interacting medications, and anticoagulation knowledge will be assessed in this study. Given that this is a pilot study we will be looking at recruitment numbers and necessary parameter estimates to determine the number of patients available at our institution for the study. Power analysis will be performed to evaluate the treatment effect size between the placebo and intervention groups.

Ages Eligible for Study:   18 Years and older   (Adult, Senior)
Sexes Eligible for Study:   All
Accepts Healthy Volunteers:   No

Inclusion Criteria:

  • >= 18 years old
  • Have been on warfarin anticoagulation for at least 9 months
  • Have an INR target range of 2.0-3.0
  • Have "unstable" anticoagulation control, defined as in the preceding 6 months having at least 3 INRs out of range (>= 3.2 or =<1.8) or at least 3 warfarin dose changes
  • Have anticoagulation managed by the Ottawa Hospital Thrombosis Clinic
  • Able to provide written, informed consent

Exclusion Criteria:

  • Anticipated interruption or termination of warfarin anticoagulation in the next six months for a period of 1 week or greater
  • Patient instability in the preceding six months suspected to be due to a) Interruption of warfarin therapy for a period of 1 week or more or b) Significant non-compliance (assessed from patient record)
  • Possess a known allergy to Vitamin K or lactose based placebos
  • Unable/Refusal to provide written, informed consent
  Contacts and Locations
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Please refer to this study by its identifier: NCT00794755

Canada, Ontario
Ottawa Hospital Thrombosis Clinic
Ottawa, Ontario, Canada, K1Y4E9
Sponsors and Collaborators
Ottawa Hospital Research Institute
Principal Investigator: Philip S Wells, MD, MSc Ottawa Hospital, Ottawa Health Research Institute
  More Information

Responsible Party: Dr. Philip S Wells (Chair, Department of Medicine), Ottawa Hospital Research Institute (OHRI) Identifier: NCT00794755     History of Changes
Other Study ID Numbers: OHREB #2008555-01H
Study First Received: November 18, 2008
Last Updated: July 26, 2011

Keywords provided by Ottawa Hospital Research Institute:
Vitamin K
Vitamin K1 (Phytonadione)
Unstable INR
VTE or Thrombosis
Anticoagulation Control
Patients on warfarin with unstable anticoagulation control

Additional relevant MeSH terms:
Vitamin K
Vitamin K 1
Growth Substances
Physiological Effects of Drugs
Antifibrinolytic Agents
Fibrin Modulating Agents
Molecular Mechanisms of Pharmacological Action
Anticoagulants processed this record on April 28, 2017