Co-administering broad-spectrum antibiotics alongside coumarin anticoagulants can cause the anticoagulant efficacy to be____________?
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Answer: C. Increased because of reduction of vitamin sources
Explanation
Broad-spectrum antibiotics destroy normal intestinal flora producing vitamin K. Reduced vitamin K availability diminishes hepatic synthesis of vitamin K-dependent clotting factors. This synergy enhances the hypoprothrombinemic response and increases anticoagulant efficacy. Coumarin anticoagulants inhibit the vitamin K epoxide reductase enzyme complex. Intestinal bacteria normally synthesize significant amounts of vitamin K for host absorption. Depleting this vitamin source enhances the anticoagulant potency of coumarin drugs.
Patients taking warfarin require careful INR monitoring when starting new antibiotics. Enhanced anticoagulant efficacy can lead to serious bleeding complications if unmonitored. Clinicians adjust anticoagulant dosages proactively to maintain therapeutic target ranges. Option A is incorrect because metabolism is not enhanced by this mechanism. Option B is wrong since protein binding is not the primary factor altered here. Option D incorrect because renal excretion does not cause this specific interaction.
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