What is meant by the 'therapeutic index' of a drug?

The therapeutic index of a drug is defined as the ratio of the toxic dose to the therapeutic dose. This measurement provides crucial insights into the safety and effectiveness of a medication. A higher therapeutic index indicates a wider margin between the dose that produces a therapeutic effect and the dose that could cause toxicity, meaning the drug is generally safer for use in patients. Conversely, a drug with a low therapeutic index has a narrow margin, suggesting a higher risk of adverse effects at doses close to the therapeutic level.

Understanding the therapeutic index is vital for healthcare professionals, as it helps guide dosage decisions and the monitoring of patients during treatment. This concept is particularly important in the management of drugs with narrow therapeutic indices, where precise dosing is critical to avoid toxicity or therapeutic failure.