What does a narrow therapeutic index indicate?

A narrow therapeutic index refers to a small range between the minimum effective dose and the minimum toxic dose of a medication. This means that there is a low margin of safety; a slight increase in dose can lead to toxicity, while a slight decrease can lead to ineffectiveness. Therefore, drugs with a narrow therapeutic index require careful monitoring of blood levels and dosages to avoid adverse effects and ensure therapeutic efficacy.

This characteristic is critical in pharmacotherapy, as it directly influences how a drug should be prescribed, monitored, and adjusted. Medications with a narrow therapeutic index often include certain anticonvulsants, warfarin, and lithium, which necessitate frequent monitoring to maintain the concentration of the drug within the therapeutic window.

Understanding this concept is fundamental for healthcare professionals when determining dosing protocols and assessing patient safety.