Therapeutic Index & Antidote Lab

Scene

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Dose

Administered dose 10 mg

Log scale — drag far right to explore a large accidental overdose.

Wide therapeutic index

Effect

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Toxicity

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TI = TD50/ED50

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Status

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Narrow therapeutic index

Effect

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Toxicity

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TI = TD50/ED50

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Status

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How it works

Each drug gets two Hill-equation curves that share a dose axis: an effect curve (desired action) and a toxic curve (harmful action). The horizontal gap between the two curves is the safety margin.

effect(dose) = 100 · dose^n / (dose^n + ED50^n)
toxic(dose)  = 100 · dose^n / (dose^n + TD50^n)
TI = TD50 / ED50

Wide TI — TD50 sits far above ED50, so the green safety band stretches across most of the dose range; a big dosing error still lands short of toxicity.
Narrow TI — TD50 sits close to ED50, so the band is thin; a small overdose already crosses into the red toxic zone.

Wide-TI effect / toxic Narrow-TI effect / toxic

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