Which antibiotic is listed as enhancing the anticoagulant effect of warfarin?

Which antibiotic is listed as enhancing the anticoagulant effect of warfarin?

• A. Clarithromycin/erythromycin
• B. Cephalosporins
• C. Metronidazole
• D. PRP

Answer: (A)

Warfarin levels and its anticoagulant effect can be boosted by certain antibiotics through two main routes: slowing the liver's breakdown of warfarin and reducing the gut bacteria that produce vitamin K. Macrolide antibiotics, such as erythromycin and clarithromycin, are classic examples because they strongly inhibit the enzymes that metabolize warfarin and can significantly raise its activity. As a result, the INR can rise and the risk of bleeding increases, so this combination is well known and should be monitored closely or avoided if possible. Other options either act less predictably on warfarin or work through different mechanisms. Cephalosporins may carry a bleeding risk by lowering vitamin K–producing bacteria but don’t consistently equal the metabolic interaction macrolides have. Metronidazole can also enhance warfarin effects, but the most recognized and commonly cited paired interaction in many lists is with macrolides. PRP isn’t an antibiotic, so it doesn’t fit.

Warfarin levels and its anticoagulant effect can be boosted by certain antibiotics through two main routes: slowing the liver's breakdown of warfarin and reducing the gut bacteria that produce vitamin K. Macrolide antibiotics, such as erythromycin and clarithromycin, are classic examples because they strongly inhibit the enzymes that metabolize warfarin and can significantly raise its activity. As a result, the INR can rise and the risk of bleeding increases, so this combination is well known and should be monitored closely or avoided if possible.

Other options either act less predictably on warfarin or work through different mechanisms. Cephalosporins may carry a bleeding risk by lowering vitamin K–producing bacteria but don’t consistently equal the metabolic interaction macrolides have. Metronidazole can also enhance warfarin effects, but the most recognized and commonly cited paired interaction in many lists is with macrolides. PRP isn’t an antibiotic, so it doesn’t fit.