What defines a drug with a narrow therapeutic index?

A drug with a narrow therapeutic index is defined by the small difference between therapeutic and toxic doses. This characteristic means that the range of dosages that produces the desired therapeutic effect is very close to the range that could result in toxicity. Consequently, even a slight increase in dose can lead to adverse effects or toxicity, making careful monitoring essential when administering such medications.

Drugs with a narrow therapeutic index require clinicians to be diligent in their dosing strategies and monitoring protocols to prevent toxicity while still achieving therapeutic effect. This necessity for meticulous oversight distinguishes these drugs from those with a wide therapeutic index, where there is a larger margin of safety and less risk involved in dosing adjustments.