Which of the following may increase the effect of an anticoagulant and thus is a potential interaction?

• A. Certain Antibiotics, Antifungals, And Anticonvulsants
• B. NSAIDs
• C. Vitamin C Supplements
• D. Moderate Caffeine Intake

Answer: (A)

Drug interactions that boost an anticoagulant’s effect happen when other medicines change how the anticoagulant is processed or how much vitamin K is available for clotting. Broad-spectrum antibiotics can wipe out gut bacteria that produce vitamin K, lowering vitamin K levels and allowing the anticoagulant to work more strongly, which raises bleeding risk. Some antifungals, especially certain azole drugs, inhibit liver enzymes that normally metabolize anticoagulants, so the drug stays in the body longer and its effect increases. Anticonvulsants can also alter enzyme activity or how the drug binds, and in some cases this leads to higher anticoagulant activity or more variability in response.

NSAIDs don’t increase the anticoagulant’s level themselves; they mainly raise bleeding risk by inhibiting platelet function, which is a different kind of interaction. Vitamin C supplements and moderate caffeine intake don’t have meaningful, consistent effects on anticoagulant activity.