Probable drug interaction between warfarin and hormonal contraceptives

The Annals of Pharmacotherapy
Michelle M ZingoneDiana Cobb

Abstract

To report a single patient case that presented with a probable drug interaction between warfarin and 3 methods of hormonal contraceptives, as assessed by the Horn Interaction Probability Scale. A 33-year-old female patient required long-term anticoagulation following an aortic valve replacement. While taking warfarin (38.5 mg weekly), she transitioned from a monophasic combined oral contraceptive (ethinyl estradiol plus norethindrone) to an implantable progestin-only contraceptive (etonogestrel) on the advice of her cardiologist. Nineteen days following etonogestrel implant insertion, her international normalized ratio (INR) decreased to 1.8 and required a 55.8% warfarin dose increase (resulting dose of 60 mg weekly). Within 10 months, the patient elected to have the implant removed due to vaginal bleeding. Nine days following removal of etonogestrel, she experienced a transient INR increase to 6.5. Her INR returned to within goal range after her warfarin dose was decreased to 55.5 mg weekly. After using barrier methods of contraception for 48 days, she initiated an oral progestin-only contraceptive (norethindrone). Further warfarin dose adjustments were made, resulting in a weekly warfarin dose of 53.5 mg. Thirty-nine days aft...Continue Reading

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Citations

May 12, 2011·Reviews in Endocrine & Metabolic Disorders·Thomas G DeLoughery
May 1, 2015·European Heart Journal·Jolien W Roos-HesselinkMark R Johnson
Apr 16, 2016·Clinical Pharmacology and Therapeutics·Yasar TasnifMary F Hebert
Apr 16, 2011·The Journal of Pharmacology and Experimental Therapeutics·Jessica MwinyiMagnus Ingelman-Sundberg
Jul 24, 2015·Blood Coagulation & Fibrinolysis : an International Journal in Haemostasis and Thrombosis·Verena WalshMartin J Shearer
Jan 27, 2019·Congenital Heart Disease·Ginnie AbarbanellSherry L Farr

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