OBJECT DRUGS

Anticoagulants, Oral:

• Acenocoumarol
• Phenprocoumon
• Warfarin (Coumadin, etc.)

PRECIPITANT DRUGS

Thyroid:

• Levothyroxine (Synthroid, etc.)
• Liothyronine (Cytomel, etc.)
• Liotrix (Thyrolar, etc.)
• Thyroid USP

Comment:

When thyroid hormones are started in the presence of oral anticoagulant therapy, the hypoprothrombinemic response increases gradually (thyroxine has a long half-life). The risk is probably minimal if anticoagulation therapy is started in a euthyroid patient stabilized on thyroid replacement therapy.

Class 3: Assess Risk & Take Action if Necessary

• Monitor: Monitor for altered anticoagulant response if thyroid is initiated, discontinued or changed in dosage. Note that since the effect is gradual, monitoring may be needed for several weeks (sometimes more) until the hypoprothrombinemic response stabilizes.