Figure 3-37 Relationships among the median effective dose (ED₅₀ ), median lethal dose (LD₅₀ ), and therapeutic index. These curves were generated from data on animals that were injected with various doses of a sedative-hypnotic and the clinical responses determined. ED₅₀ is the dose of drug required to produce a specific effect (i.e., hypnosis) in 50% of animals to which it is administered (left curve). LD₅₀ is the dose of drug required to produce death in 50% of animals to which drug is administered (right curve). The therapeutic index of the drug is the ratio between LD₅₀ and ED₅₀ (LD₅₀ /ED₅₀ ). LD₁ is the lethal dose in 1% of the population, and ED₉₉ is the effective dose in 99% of the population. As drawn, LD₁ < ED₉₉ , which would not be clinically acceptable.