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Divides the toxic dose by the effective dose to give the therapeutic index, the classic measure of a drug's safety margin.
Therapeutic index
TI = TD50 / ED50 (or LD50 / ED50); a value below about 2 marks a narrow therapeutic index drug
Educational estimate only. Not a substitute for professional clinical judgement, and must not be used to make treatment or dosing decisions.
Warfarin, digoxin, lithium, phenytoin, theophylline and aminoglycosides are the classic examples.
It means dose-related toxicity is less likely, but idiosyncratic and allergic reactions are unrelated to the index.