Therapeutic range

The therapeutic range of a drug is the distance between its therapeutic dose and a dose that leads to a toxic effect. The greater the therapeutic range, the safer the drug. This is generally expressed as a "therapeutic quotient", which is calculated as follows: ED50 (average effective dose), dose at which the desired therapeutic effect occurs in 50% of individuals /LD50 (average lethal dose), dose at which 50% of individuals die.

Drugs with a broad therapeutic range include, for example, glucocorticoids, penicillin and other β-lactam antibiotics. Drugs with a narrow therapeutic range include digitalis cardiac glycosides. Similarly, many narcotics are characterized by a low therapeutic range. Their effect, the depth of anaesthesia, must therefore be constantly monitored over time.

1. Schöldgen W (1968) Application possibilities and therapeutic range of a new steroid emulsion ("Lotio") . Dtsch Med J 19:187-188.