CC22 – Therapeutic index
CC22. Therapeutic index, a measure of drug safety, is the ratio between the dose/concentration of a drug producing toxicity and the dose/ concentration that produces a therapeutic effect.
22.1. In order to calculate the therapeutic index of a drug, the median effective dose (ED50) and the median toxic dose (TD50) or median lethal dose (LD ) are derived from quantal log dose–response curves.
22.2. The therapeutic index is calculated by dividing the TD50 (or LD50) by the ED50.
22.3. The larger the therapeutic index, the more favourable the drug’s margin of safety.
22.4. When administering a drug with a low therapeutic index, greater care needs to be taken to minimise drug toxicity, including monitoring its plasma concentration.
