Warfarin and amoxicillin/clavulanate drug interaction.
OBJECTIVE
To report a case of warfarin-amoxicillin/clavulanate potassium (AM/CL) interaction resulting in an elevated international normalized ratio (INR) and hematuria.


METHODS
A 58-year-old Hawaiian/Asian/European woman developed an elevated INR and microscopic hematuria as a result of a drug-drug interaction between warfarin and AM/CL.


CONCLUSIONS
Our report of an increased INR with bleeding complications as a result of an interaction between warfarin and AM/CL is consistent with those in the literature. Although the mechanism for this interaction is not fully known, it is suspected that a decrease in vitamin K-producing gut flora with resulting vitamin K deficiency would be the most likely contributing factor. An objective causality assessment revealed that this adverse drug event as a result of the warfarin and AM/CL interaction was possible.


CONCLUSIONS
An increased INR secondary to warfarin interactions with various antibacterial agents is a known phenomenon. An increased awareness of warfarin-AM/CL interaction and appropriate monitoring are essential to control the INR levels and prevent bleeding complications.
Davydov
Liya
L
Department of Pharmacy, St. John's Episcopal Hospital, Far Rockaway, NY, USA. ldavydov@fedeliscare.org.
Yermolnik
Marina
M
Cuni
Lewis J
LJ
D019980:Amoxicillin-Potassium Clavulanate Combination / Q000009:adverse effects*; D000925:Anticoagulants / Q000009:adverse effects*; D000933:Antifibrinolytic Agents / Q000627:therapeutic use; D001803:Blood Transfusion; D004347:Drug Interactions; D004359:Drug Therapy, Combination / Q000009:adverse effects*; D005260:Female; D006417:Hematuria / Q000139:chemically induced / Q000628:therapy; D006801:Humans; D019934:International Normalized Ratio; D008875:Middle Aged; D014812:Vitamin K / Q000627:therapeutic use; D014859:Warfarin / Q000009:adverse effects*
D000925:Anticoagulants; D000933:Antifibrinolytic Agents; D014812:Vitamin K; D014859:Warfarin; D019980:Amoxicillin-Potassium Clavulanate Combination