Coumadin and Oseltamivir

In the database of official manuals used in the service creation an interaction registered by statistical results of studies was found, which can either lead to negative consequences for the patient health or strengthen a mutual positive effect. A doctor should be consulted to address the issue of joint drug administration.

Consumer information for this minor interaction is not currently available. Some minor drug interactions may not be clinically relevant in all patients. Minor drug interactions do not usually cause harm or require a change in therapy. However, your healthcare provider can determine if adjustments to your medications are needed.

Limited data suggest that oseltamivir may potentiate the hypoprothrombinemic effect of warfarin. The mechanism of interaction is unknown, as oseltamivir has not been shown to interfere with coagulation or inhibit any CYP enzymes, specifically those involved in the metabolism of warfarin. Oseltamivir is also not subject to extensive protein binding. A formal drug-drug interaction study in 20 healthy volunteers stabilized on warfarin found no significant effect of oseltamivir (75 mg twice daily for 4.5 days) on the pharmacokinetics and pharmacodynamics of warfarin, yet there have been case reports of increased INR associated with oseltamivir use. Both the U.K. Medicines and Healthcare Products Regulatory Agency and Health Canada have received and evaluated suspected reports of the interaction, although a causal relationship could not be established in most cases due to conflicting or insufficient clinical information and potential confounding factors. A retrospective review conducted by investigators at a South Korea hospital identified fifteen patients who took warfarin with oseltamivir over a 6 month period between September 2009 and February 2010. Of the 15 patients, seven had an increase in INR levels following oseltamivir administration (mean INR increased from 2.08 to 5.15), and three had bleeding events including blood-tinged sputum and bloody ascites. In addition, one patient subsequently had a positive rechallenge. A retrospective cohort study using Medicare claims data from June 30, 2006 to October 31, 2010 found only a modest, but statistically significant, increase in bleeding events in patients who received warfarin and oseltamivir compared to controls (i.e., patients who received warfarin and an ACE inhibitor), the most frequent being epistaxis. However, as the investigators pointed out, influenza patients may have had an increased risk of epistaxis due in part to increased nasal discharge. Moreover, stress and infection can also affect coagulation, as well as fever and dietary changes associated with illness. In the absence of strong evidence or a biologically plausible mechanism, the risk of interaction between oseltamivir and warfarin appears to be low.

Coumadin

Generic Name: warfarin

Brand name: Coumadin, Jantoven

Synonyms: n.a.

What is Coumadin?

Oseltamivir

Generic Name: oseltamivir

Brand name: Tamiflu

Synonyms: n.a.

What is Oseltamivir?