Which of the following drugs is classified as a narrow therapeutic index drug?

Warfarin is classified as a narrow therapeutic index (NTI) drug. This classification indicates that there is a small margin between the therapeutic dose and the dose that could lead to toxicity. Because of this narrow margin, patients on warfarin must be closely monitored through regular blood tests, specifically checking the International Normalized Ratio (INR), to ensure they remain within the therapeutic range.

For medications like warfarin, even slight variations in dosage, diet, or drug interactions can result in significant changes in anticoagulation effects, which can lead to serious health risks such as bleeding complications. Understanding this risk is crucial for managing patients effectively while they are on warfarin therapy.

In contrast, the other options, such as aspirin, acetaminophen, and ibuprofen, generally have wider therapeutic indices, meaning there is a greater safety margin between therapeutic and toxic doses. While these medications can still cause adverse effects, the monitoring of their dosing is not as critical as it is for warfarin.