Danazol increases the anticoagulant effect of warfarin.
OBJECTIVE
To report two cases demonstrating an interaction between danazol and warfarin, resulting in the potentiation of warfarin's effect and bleeding complications.


METHODS
Case reports, review articles, and studies identified by MEDLINE.


METHODS
All published English-language reports involving danazol and warfarin interactions were reviewed.


RESULTS
Danazol, a synthetic testosterone derivative, is used in the treatment of endometriosis, fibrocystic breast disease, menorrhagia protein C deficiency, and hemophilia. We describe two cases including an interaction between danazol and warfarin, resulting in bleeding complications. There are at least two other reported cases of this interaction. This interaction may be attributable to several mechanisms. Danazol may inhibit the metabolism of warfarin and/or it may have a direct effect on the coagulation and fibrinolytic systems.


CONCLUSIONS
Based on this report and other published cases, clinicians must be aware that danazol may increase the anticoagulant effect of warfarin. Patients receiving warfarin who are prescribed danazol must be monitored closely to prevent excessive anticoagulation and subsequent bleeding. Studies are needed to determine the frequency of this interaction and its underlying mechanisms.
Meeks
M L
ML
Department of Pharmacy Services, University of Arizona Health Sciences Center, Tucson.
Mahaffey
K W
KW
Katz
M D
MD
D000328:Adult; D002561:Cerebrovascular Disorders / Q000188:drug therapy; D003613:Danazol / Q000008:administration & dosage / Q000494:pharmacology*; D004357:Drug Synergism; D005260:Female; D006801:Humans; D008875:Middle Aged; D011517:Prothrombin Time; D014859:Warfarin / Q000008:administration & dosage / Q000494:pharmacology*
D014859:Warfarin; D003613:Danazol