What does a narrow therapeutic range indicate?

A narrow therapeutic range indicates a small difference between the minimum effective concentration and the toxic concentration of a drug. This means that there is a limited margin between the dose that produces the desired therapeutic effect and the dose that leads to toxicity.

In clinical practice, drugs with a narrow therapeutic range require careful monitoring and precise dosing to avoid adverse effects, ensuring that drug levels remain within a safe and effective range. If the concentration of the drug in the bloodstream falls below the minimum effective level, the therapeutic effects will not be achieved. Conversely, if the concentration rises above the toxic level, it can lead to harmful side effects or overdose.

This concept is particularly relevant for medications such as warfarin, digoxin, and lithium, where small changes in dosage or absorption can lead to significant therapeutic or toxic outcomes. Therefore, understanding that a narrow therapeutic range means careful management of drug levels is essential for patient safety and effective treatment.