The anticoagulant effects of acenocoumarol, dicoumarol, phenindione, and
warfarin are increased by
thyroid hormones and bleeding has been seen. This is largely due to alteration of
thyroid function, rather than a direct
drug-drug interaction.
Hypothyroid patients taking an anticoagulant who are subsequently given
thyroid hormones as replacement therapy will need a downward adjustment of the anticoagulant dosage as treatment proceeds. Monitor the INR and adjust the
warfarin as necessary.