Pharmacology & Dosage
Basic

Therapeutic Index

Ratio of the dose causing toxicity to the effective dose — a safety measure for drugs.

Formula

TI=TD50ED50TI = \frac{TD_{50}}{ED_{50}}

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Variables

TITherapeutic index
TD_{50}Dose toxic to 50 % of subjects
ED_{50}Dose effective in 50 % of subjects

Example

TD₅₀ = 600 mg, ED₅₀ = 100 mg → TI = 6

Did You Know?

Warfarin and lithium have notoriously narrow therapeutic indices — even small dose errors can be dangerous.

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