Dangerous Drug Interaction: Warfarin-Quinolones
| warfarin (Coumadin) |
alatrofloxacin (Tolectin, Tolectin DS)
cinoxacin (Cinobac)
ciprofloxacin (Cipro)
enoxacin (Penetrex)
gatifloxacin (Tequin)
levofloxacin (Levaquin)
lomefloxacin (Maxaquin)
moxifloxacin (Avelox)
nalidixic acid (NegGram)
norfloxacin (Noroxin)
ofloxacin (Floxin)
sparfloxacin (Zagam)
trovafloxacin (Trovan, Trovan IV) |
| Brand names appear in parentheses above and are trademarks of their respective manufacturers/owners. |
Impact: Potential for increased effects of warfarin1
Mechanism of Interaction: The exact warfarin-quinolone drug interaction is unknown. Reduction of intestinal flora responsible for vitamin K production by antibiotics is probable as well as decreased metabolism and clearance of warfarin.
Alternatives to Patient Management: Culture and identify microbial pathogen prior to initiation of antibiotic therapy. Consider culture sensitivity screening. The metabolism of warfarin may be delayed in patients administered enoxacin,4 ciprofloxacin,4,5 norfloxacin,4 or ofloxacin4; thus, quinolone selection should focus on one of the newer agents that has not demonstrated significant impairment of warfarin metabolism, such as levofloxacin. Additionally, microbial pathogen identification and sensitivity prior to antibiotic initiation will decrease the prevalence of unnecessary drug interaction risk.
Monitoring/Precautions: INR should be monitored during co-administration of warfarin with a quinolone. If use of ciprofloxacin is imperative, then monitor INR every other day and adjust warfarin dose as necessary.2 Signs and symptoms of an active bleed should be monitored daily with particular attention to the appearance and patterns of bruises. Signs of an active bleed include: coughing up blood in the form of coffee grinds (hemoptysis), gingival bleeding, nose bleeds, cola- or tea-colored urine (hematuria), and black, tarry stools (hemoccult positive?).
References: Follow this link for a complete list of references.
The above information serves only as a guide for use by qualified medical practitioners in understanding, handling and avoiding frequent and potentially dangerous drug interactions that occur in long-term care. This presentation is not intended to instruct a practitioner how to treat any medical condition, nor is it intended to replace a practitioner's best clinical judgment. AMDA expressly disclaims responsibility and liability for any adverse effects, damages or other consequences resulting from the use of any of the information contained in this presentation.
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