What is meant by 'narrow therapeutic index'?

A 'narrow therapeutic index' refers to a situation in pharmacology where there is a small margin between the minimum effective dose and the minimum toxic dose of a drug. This means that only a slight increase in dosage can lead to adverse effects, while a slight decrease might result in subtherapeutic efficacy. This characteristic is critical for ensuring that the drug is used safely and effectively.

Drugs with a narrow therapeutic index require careful monitoring and precise dosing, as both underdosing and overdosing can occur easily within this small range. Consequently, options that suggest a wide range of effective dosing, high toxicity levels without specificity, or a broad spectrum of therapeutic uses do not accurately depict the concept of a narrow therapeutic index. Instead, the focus is on the crucial and delicate balance needed in dosing such drugs, which is effectively reflected in the knowledge that a small difference in drug dosage can lead to significant and varying effects.