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Possible warfarin failure due to interaction with smokeless tobacco
Jim R Kuykendall1, Michael D Houle, Richard S Rhodes
1Department of Biopharmaceutical Sciences, Raabe College of Pharmacy, Ohio Northern University, Ada, OH 45810-1599, USA. j-kuykendall@onu.edu
The Annals of Pharmacotherapy
|February 10, 2004
Summary
Smokeless tobacco use may interfere with warfarin therapy due to high vitamin K content, potentially reducing its effectiveness. Patients on warfarin should have their smokeless tobacco use documented to manage potential drug interactions.
Area of Science:
- Pharmacology
- Drug Interactions
- Cardiovascular Medicine
Background:
- Warfarin is a common anticoagulant used to prevent thromboembolic events.
- Smokeless tobacco is a nicotine-containing product with potential pharmacological activity.
- Managing anticoagulation in patients with multiple cardiovascular events can be challenging.
Observation:
- A patient with a history of multiple myocardial infarctions and strokes used smokeless tobacco.
- Warfarin therapy (up to 25-30 mg/day) failed to achieve therapeutic International Normalized Ratio (INR) levels (>2.0) for 4.5 years.
- INR levels increased from 1.1 to 2.3 within one week after discontinuing smokeless tobacco.
Findings:
- Smokeless tobacco contains high levels of vitamin K, a known antagonist of warfarin.
- The probable interaction mechanism involves increased dietary vitamin K from tobacco, counteracting warfarin's anticoagulant effect.
- Cessation of smokeless tobacco led to improved INR values, suggesting a direct interaction.
Implications:
- Smokeless tobacco use should be routinely assessed and documented in patients prescribed warfarin.
- Healthcare providers should counsel patients on the potential for drug interactions between tobacco products and anticoagulants.
- Further research is needed to elucidate the precise pharmacokinetic and pharmacodynamic mechanisms of this interaction.