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Dear Debra,
As you can see, it is often challenging to correctly regulate INR levels during coumadin therapy. Although many medications can either increase or reduce the INR, lasix and vasotec are not common offenders. Incidentally, thyroxine(synthroid) can increase the INR by speeding up the metabolism of the clotting factors that coumadin also antagonizes. Thus, I don't think that it is to blame in this case. It is likely that increased dosages of coumadin will achieve the goal INR that you and your doctors are aiming for (typically 2.5 to 3.5 for mechanical heart valves). Dosages of 10mg a day are not unusual. Of note, you might want to check that your mother is not consuming excessive amounts of leafy-green vegetables or taking vitamin supplements that may contain Vitamin K. Finally, some patients are relatively resistant to Vitamin K due to gastrointestinal factors. Larger doses may be necessary in such patients.
Best of luck. Information provided in the Heart Forum is for general purposes only. Specific diagnoses and therapies can only be provided by your physician.