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Study of Genetic Factors Other Than CYP2C9 and VKORC1 That Influence Warfarin Dose Requirements in a South-east Asian Population

The recruitment status of this study is unknown. The completion date has passed and the status has not been verified in more than two years.
Verified January 2014 by National University Hospital, Singapore.
Recruitment status was:  Recruiting
Information provided by:
National University Hospital, Singapore Identifier:
First received: January 15, 2010
Last updated: January 21, 2014
Last verified: January 2014
Warfarin is a commonly used anti-coagulant, but has a narrow therapeutic index and wide inter-individual and inter-ethnic variation in dose requirements. Several genetic and non-genetic factors have been identified that could influence warfarin dose requirements. However, current known predictive factors could only explain about 50-60% of warfarin dose variability. Inter-ethnic differences in genetic influences on warfarin dose requirements also exist. We hypothesize that genetic factors other than CYP2C9 and VKORC1 may influence warfarin dosing and serve to further optimize warfarin dosing.

Condition Intervention
Cancer Biological: Blood collection

Study Type: Observational
Study Design: Observational Model: Cohort
Time Perspective: Cross-Sectional

Resource links provided by NLM:

Further study details as provided by National University Hospital, Singapore:

Primary Outcome Measures:
  • To identify genetic variants other than CYP2C9 and VKORC1 that may influence warfarin dose requirements in a multi-ethnic population in Singapore.

Study Start Date: September 2013
Estimated Study Completion Date: December 2014
Estimated Primary Completion Date: December 2014 (Final data collection date for primary outcome measure)
Groups/Cohorts Assigned Interventions
Blood Collection Biological: Blood collection


Ages Eligible for Study:   21 Years and older   (Adult, Senior)
Sexes Eligible for Study:   All
Accepts Healthy Volunteers:   No
Sampling Method:   Probability Sample
Study Population

Germline DNA will be genotyped for variants in genes in the anti-coagulation pathway, including CYP4F2, GGCX and EPHX1. The germline DNA was previously collected from a warfarin study (C/00/510, NUH, C/00/535, TTSH, PI-Dr Goh Boon Cher). Samples were anonymized, and data analysis will be done without patient identifiers. Germline DNA previously collected from 279 patients who were on maintenance warfarin dose will be genotyped.

The clinical data that has been collected and will be used for the study include: gender, race, age, body weight, maintenance warfarin dose, serum albumin, two consecutive stable INR values, and indications for warfarin use.


Inclusion Criteria:

  • patients receiving maintenance warfarin therapy with a stable therapeutic international normalized ratio (INR) between 2 and 3 for at least 3 months,
  • patients recruited from the anticoagulation clinics at the National University Hospital and Tan Tock Seng Hospital in Singapore between June 2002 and June 2004 for a previous genotyping study (C/00/510, NUH; C/00/535, TTSH, PI-Dr Goh Boon Cher).

Exclusion Criteria:

  • patients below 21 years old, or
  • patients with liver disease, malabsorption or chronic diarrheal diseases, or
  • patients taking drugs that may potentially interact with warfarin.

Dietary advice to avoid foods that may interfere with warfarin pharmacokinetics will be given to patients during warfarin therapy.

  Contacts and Locations
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Please refer to this study by its identifier: NCT01050920

Contact: Soo Chin Lee, MBBS, MRCP 65 6772 4629

National University Hospital Recruiting
Singapore, Singapore, 119074
Contact: Soo Chin Lee, MBBS, MRCP    65 6772 4629   
Sponsors and Collaborators
National University Hospital, Singapore