Standardized Safety Margin

A number, LD1-ED99/ED99 x 100%, which is a measure of the selectivity of action or relative "safety" of a drug. The standardized safety margin indicates by what percentage of itself a dose effective in virtually all (99%) of a population must be exceeded in order to produce a lethal effect in a minimum number (1%) in the population. The therapeutic index (q.v.) measures by what factor an
effective dose must be increased to produce a standard lethal effect in a population. Clinically, the standardized safety margin probably has greater practical meaning than does the therapeutic index, and, unlike the therapeutic index, the meaningfulness of the standardized safety margin does not depend on the parallelism of the dose effect curves from which the LD1 and ED99 are inferred. The standardized safety margin (more frequently than the therapeutic index) can sometimes be computed from clinical data not involving lethal effects, e.g., the ED99 for control of epileptic seizures and the ED1 for the production of drowsiness or ataxia, in a population of patients with epilepsy. See: Foster, R.H.K., J. Pharmacol. 65: 1, 1939.

Cf. Therapeutic Index, Median Effective Dose, Selectivity, Clinical Therapeutic Index