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Aspirin is a nonsteroidal anti-inflammatory drug (NSAID) that is commonly used to relieve pain, reduce inflammation, and prevent blood clots. When taken with blood thinners, such as warfarin or Coumadin, aspirin can interact with these medications and affect their dosage.

According to the American Heart Association, taking aspirin with warfarin can increase the risk of bleeding due to the synergistic effect of both medications [1]. Warfarin works by inhibiting the production of vitamin K-dependent clotting factors in the liver, while aspirin inhibits platelet aggregation and reduces the production of thromboxane A2, a potent vasoconstrictor. This combination can increase the risk of bleeding, particularly in patients with a history of gastrointestinal bleeding or those taking other anticoagulant medications.

The dosage of warfarin may need to be adjusted when taken with aspirin. The International Normalized Ratio (INR) should be closely monitored to ensure that the warfarin dosage is effective and safe. The INR is a measure of the blood's ability to clot, and an INR of 2-3 is generally considered therapeutic for patients taking warfarin.

In contrast, the combination of aspirin and clopidogrel (Plavix) may have a synergistic effect in reducing the risk of cardiovascular events, including heart attacks and strokes. A study published in the New England Journal of Medicine found that patients taking aspirin and clopidogrel had a significant reduction in cardiovascular events compared to those taking aspirin alone [2].

In conclusion, the interaction between aspirin and blood thinners can have significant effects on their dosages and efficacy. Patients taking these medications should work closely with their healthcare providers to monitor their INR and adjust their dosages as needed. Additionally, patients should be aware of the potential risks and benefits of combining aspirin with blood thinners and discuss any concerns with their healthcare providers.

Sources:

[1] American Heart Association. (2019). Warfarin and Aspirin Combination Increases Bleeding Risk. Retrieved from <https://www.heart.org/en/news/2019/02/14/warfarin-and-aspirin-combination-increases-bleeding-risk>

[2] Yusuf, S., et al. (2008). Effects of clopidogrel added to aspirin in patients with acute coronary syndromes without ST-segment elevation. New England Journal of Medicine, 358(14), 1444-1453. doi: 10.1056/NEJMoa0807657

[3] DrugPatentWatch.com. (n.d.). Aspirin Patent Expirations. Retrieved from <https://www.drugpatentwatch.com/patent-expirations/aspirin>