To the Editor: We describe what we believe is the first report of a drug interaction between duloxetine hydrochloride and warfarin. The patient has provided consent for publication of this report, and it has received institutional review board approval.
A 44-year-old woman, self-designated as white, homozygous for the factor V Leiden mutation, had been treated uneventfully for 1 year after an ischemic stroke with warfarin, 7.5 to 10 mg/d (mean international normalized ratio [INR], 2.2 [SD, 0.5]) (Figure). She had normal levels of protein C, protein S, homocysteine, and lipoprotein(a); homozygous wild-type genotypes for prothrombin (G20210A), MTHFR (C677T), PAI-1 (4G/5G), and platelet glycoprotein PL A1/A2; and no lupus anticoagulant or anticardiolipin antibodies. She had increased factor XI (179% [upper normal limit, 150%]) and plasminogen activator inhibitor activity (71.7 IU/mL [upper normal limit, 21.2]). She was being treated for poststroke seizures, migraine prophylaxis, panic disorder, and bronchospasm. She had no heart failure; thyroid, hepatic, or renal disease; or major weight loss or gain. She had a normal serum albumin–globulin ratio and reported taking no complementary or alternative medications.
Glueck CJ, Khalil Q, Winiarska M, Wang P. Interaction of Duloxetine and Warfarin Causing Severe Elevation of International Normalized Ratio. JAMA. 2006;295(13):1513–1518. doi:10.1001/jama.295.13.1517
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