Which medication is monitored with PT/INR?

Which medication is monitored with PT/INR?

• A. Heparin
• B. Warfarin
• C. Aspirin
• D. Clopidogrel

Answer: (B)

PT/INR is used to monitor warfarin therapy because it reflects the activity of the extrinsic pathway of coagulation, which warfarin directly affects by reducing vitamin K–dependent clotting factors II, VII, IX, and X. When these factors are lowered, the prothrombin time (PT) lengthens, and the INR is used to standardize that result to guide dosing. Warfarin requires regular INR checks to keep anticoagulation in the therapeutic range for the patient’s condition. Heparin, on the other hand, is monitored with the aPTT (or anti-Xa for some regimens), since it primarily influences the intrinsic pathway and does not depend on vitamin K–dependent factors. Aspirin and clopidogrel are antiplatelet drugs; they affect platelet function and bleeding risk rather than the coagulation cascade measured by PT/INR, so PT/INR isn’t used to monitor them.

PT/INR is used to monitor warfarin therapy because it reflects the activity of the extrinsic pathway of coagulation, which warfarin directly affects by reducing vitamin K–dependent clotting factors II, VII, IX, and X. When these factors are lowered, the prothrombin time (PT) lengthens, and the INR is used to standardize that result to guide dosing. Warfarin requires regular INR checks to keep anticoagulation in the therapeutic range for the patient’s condition.

Heparin, on the other hand, is monitored with the aPTT (or anti-Xa for some regimens), since it primarily influences the intrinsic pathway and does not depend on vitamin K–dependent factors. Aspirin and clopidogrel are antiplatelet drugs; they affect platelet function and bleeding risk rather than the coagulation cascade measured by PT/INR, so PT/INR isn’t used to monitor them.