A
42-year-old, 111-kg, Caucasian man arrived at the emergency department with
atypical pleuritic chest pain, shortness of breath, diaphoresis, nausea,
vomiting, and tachycardia. The patient's medical history was significant for
multiple episodes of deep venous thrombosis (DVT) in the left upper extremity
and both lower extremities, a right above-the-knee amputation due to
complications of a previous DVT, insertion of a vena cava filter, pulmonary
embolism (PE), asthma, hypertension, and multiple myocardial infarctions.
During
admission, he was diagnosed presumptively with PE. All potential causes of
interference with warfarin absorption were investigated and ruled out. I.V.
warfarin therapy at a conventional initial dosage of 5 mg once daily was
started on hospital day 2. The International Normalized Ratio (INR) reached the
therapeutic range after increasing the i.v. warfarin dosage to 7.5 mg once
daily on hospital day 6. The ability to obtain a therapeutic INR on a
relatively low dosage of i.v. warfarin but not high dosages of oral warfarin
strongly suggests an inherent warfarin malabsorption defect in this patient.
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