Numerous articles report on the effects fluoroquinolone on the international normalized ratio (INR) with warfarin therapy.Proposed mechanisms of the fluoroquinolone-warfarin interaction include inhibition of the metabolism of warfarin, displacement of warfarin from protein-binding sites, and alteration of gastro-intestinal flora, resulting in reduced vitamin K synthesis.
So
Patients receiving warfarin who take gatifloxacin may be at higher risk for an INR above 4 compared with those taking levofloxacin. Close monitoring of warfarin therapy while concomitantly receiving gatifloxacin is warranted