Therapeutic Index (TI) is the ratio between a drug’s toxic dose and effective dose, indicating its safety margin.
Definition of Therapeutic Index (TI):
- The Therapeutic Index is a measure of drug safety. It compares the dose that causes toxicity to the dose that produces a therapeutic effect.
Formula:
$TI = \frac{LD_{50}}{ED_{50}}$
- TD₅₀ = dose causing toxic effect in 50
- ED₅₀ = dose producing desired effect in 50
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Interpretation:
- A higher TI = safer drug
- A low TI = narrow safety margin, needs close monitoring
(e.g., digoxin, lithium, warfarin) - A measure of drug safety.
- High TI = safer drug (e.g., penicillin).
- Low TI = narrow safety margin (e.g., digoxin, warfarin, lithium).
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