Although drug A and drug B have the same ED₅₀,drug B has a wider therapeutic index (TI);therefore,drug A has a greater LD₅₀ than drug B.

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Drug B has a wider therapeutic index.This means that drug B must be safer than drug A and that the amount of drug needed to be lethal to 50% of test animals must be greater for drug B than for drug A.Therefore,drug B has a greater LD₅₀ than drug A.The therapeutic index is the ratio of the LD₅₀ to ED₅₀.A wide therapeutic index means a greater difference between the LD₅₀ and the ED₅₀ and therefore a greater ratio.If drug B has a wider therapeutic index than drug A and the two drugs have an equivalent ED₅₀,then the LD₅₀ of drug B must be greater.

Although Drug a and Drug B Have the Same ED₅₀,drug