Which drugs are associated with decreased INR when interacting with warfarin?

Which drugs are associated with decreased INR when interacting with warfarin?

• A. Chlorpromazine or haloperidol
• B. Clozapine or olanzapine
• C. Risperidone or quetiapine
• D. Aripiprazole or lurasidone

Answer: (A)

Warfarin's anticoagulant effect is highly susceptible to drug interactions because many medications can alter its metabolism or how the vitamin K system works. When another drug decreases INR, it means warfarin’s effect is being blunted and the blood is less anticoagulated, increasing the risk of clotting. Chlorpromazine and haloperidol have been noted in clinical references to lower INR when used with warfarin. This suggests they can enhance warfarin clearance or otherwise oppose its action, leading to a reduced anticoagulant effect. Because of that, this pair best fits the idea of a drug interaction that decreases INR. The other antipsychotics listed don’t have as consistent or well-established associations with decreased INR when combined with warfarin. They may affect INR in some cases, but the pattern most repeatedly described among common interactions for this question points to chlorpromazine and haloperidol. If such a combination occurs in practice, it’s important to monitor INR closely and adjust the warfarin dose as needed to keep it in the therapeutic range.

Warfarin's anticoagulant effect is highly susceptible to drug interactions because many medications can alter its metabolism or how the vitamin K system works. When another drug decreases INR, it means warfarin’s effect is being blunted and the blood is less anticoagulated, increasing the risk of clotting.

Chlorpromazine and haloperidol have been noted in clinical references to lower INR when used with warfarin. This suggests they can enhance warfarin clearance or otherwise oppose its action, leading to a reduced anticoagulant effect. Because of that, this pair best fits the idea of a drug interaction that decreases INR.

The other antipsychotics listed don’t have as consistent or well-established associations with decreased INR when combined with warfarin. They may affect INR in some cases, but the pattern most repeatedly described among common interactions for this question points to chlorpromazine and haloperidol.

If such a combination occurs in practice, it’s important to monitor INR closely and adjust the warfarin dose as needed to keep it in the therapeutic range.