Warfarin resistance

Warfarin resistance is a rare condition in which people have varying degrees of tolerance to the anticoagulant drug warfarin.

Warfarin tablets various doses

Incidence

The exact incidence is not known but it is thought to be a very rare disease

Types

There are two types of warfarin resistance: incomplete and complete. Those with incomplete warfarin resistance can achieve the benefits of warfarin treatment with a high dose of warfarin.

Complete warfarin resistance

Individuals with complete warfarin resistance do not respond to warfarin treatment, no matter how high the dose. If people with warfarin resistance require anticoagulant therapy and take the average warfarin dose, they will remain at risk of developing a potentially harmful blood clot.

Warfarin

Incomplete warfarin resistance

In incomplete warfarin resistance, people only respond to high doses of warfarin; in complete warfarin resistance, the drug has no effect. This can be because the drug is metabolized quickly or because the clotting cascade does not interact with warfarin as it should.

Genetics

One gene that has been identified in warfarin resistance is VKORC1, a gene responsible for warfarin metabolism.

Inheritance

It is inherited in an autosomal dominant pattern.

Other names

• Coumarin resistance
• Poor metabolism of coumarin

Latest research

• Most recent articles
• Ongoing trials
• Possible warfarin resistance due to interaction with ascorbic acid: case report and literature review.'

Sattar A, Willman JE, Kolluri R. Am J Health Syst Pharm. 2013 May 1;70(9):782-6. doi: 10.2146/ajhp110704. PMID: Review. For more than a week, his International Normalized Ratio (INR) values remained below target as the dosage of warfarin was gradually increased to 20 mg daily. 

• Warfarin resistance.

Sinxadi P, Blockman M. Review. Warfarin, the only available oral coumarin anticoagulant in South Africa, is widely prescribed for the prevention and management of arterial and venous thrombo-embolism. 

• Low warfarin resistance frequency in Norway rats in two cities in China after 30 years of usage of anticoagulant rodenticides.

Pest Manag Sci. 2018 Nov;74(11):2555-2560. doi: 10.1002/ps.5040. Epub 2018 Jun 9. Laboratory resistance tests suggested low warfarin resistance frequencies in rats from Zhanjiang (4.9-17.1%) and Harbin (0-2.5%) Cities. 

• Diagnosis and treatment of warfarin resistance.

Zhong Nan Da Xue Xue Bao Yi Xue Ban. 2013 Mar;38(3):313-7. doi: 10.3969/j.issn.1672-7347.2013.03.016. Chinese. Once warfarin resistance is diagnosed, the type of resistance should be determined as soon as possible so that treatment could be oriented toward the causes.

• Warfarin resistance: diagnosis and therapeutic alternatives.

Hulse ML. Warfarin resistance may develop as a result of noncompliance, exogenous consumption of vitamin K, and concurrent ingestion of other agents known to decrease warfarin's effects.

Warfarin resistance Resources
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