title: Interaction of doxycycline and warfarin: an enhanced anticoagulant effect.
abstract: OBJECTIVE
  To highlight the importance of recognizing the increased anticoagulant effect of warfarin associated with use of doxycycline.
  
  
  METHODS
  Case report.
  
  
  METHODS
  Clinical review describing initial presentation, course, and outcome of one patient who received oral doxycycline for corneal melt while on warfarin in a multi-specialty clinic.
  
  
  RESULTS
  Concomitant use of doxycycline and warfarin resulted in prominent ecchymosis of the upper extremities associated with a marked elevation in the international normalized ratio (INR = 6.5). Discontinuation of doxycycline resulted in reduction of INR to therapeutic levels (INR = 2.3).
  
  
  CONCLUSIONS
  Doxycycline can enhance the anticoagulant effect of warfarin. This is likely due to competitive interaction for albumin binding and possibly inhibition of the cytochrome P-450 system. An increase in plasma levels of free warfarin may result in severe bleeding. It is important to recognize this potential interaction and obtain a complete medication profile prior to initiating doxycycline.
authors.affiliation: Mayo Clinic, Jacksonville, FL 32224, USA. Hasan.saiyid@mayo.edu
authors.forename: Saiyid Akbar
authors.initials: SA
authors.lastname: Hasan
mesh_terms: D000284:Administration, Oral; D000369:Aged, 80 and over; D000900:Anti-Bacterial Agents / Q000009:adverse effects* / Q000627:therapeutic use; D000925:Anticoagulants / Q000009:adverse effects* / Q000627:therapeutic use; D003320:Corneal Ulcer / Q000188:drug therapy; D004318:Doxycycline / Q000009:adverse effects* / Q000627:therapeutic use; D004347:Drug Interactions; D004359:Drug Therapy, Combination; D004438:Ecchymosis / Q000139:chemically induced*; D006801:Humans; D019934:International Normalized Ratio; D008297:Male; D014859:Warfarin / Q000009:adverse effects* / Q000627:therapeutic use
chemical_list: D000900:Anti-Bacterial Agents; D000925:Anticoagulants; D014859:Warfarin; D004318:Doxycycline