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Therapeutic Index Calculator

Work out therapeutic index instantly with clear inputs, formula shown and shareable results.

About Therapeutic Index Calculator

Divides the toxic dose by the effective dose to give the therapeutic index, the classic measure of a drug's safety margin.

Formula

Therapeutic index

TI = TD50 / ED50 (or LD50 / ED50); a value below about 2 marks a narrow therapeutic index drug

Worked example

With the default values below, Therapeutic Index Calculator returns Therapeutic index of 10.000. Change any input above and every figure here is recalculated in your browser.

Inputs used

Toxic dose (TD50 or LD50)accepts 0.1–100,000 mg
400 mg
Effective dose (ED50)accepts 0.1–100,000 mg
40 mg

Results

Therapeutic index
10.000
Interpretation
Wide margin
Margin above the effective dose
900.0%

Step by step

  1. 1Values used
  2. 2Therapeutic index
  3. 3Therapeutic index= 10.000
  4. 4Interpretation= Wide margin
  5. 5Margin above the effective dose= 900.0

Assumptions and limits

  • The result is derived only from the 2 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 3 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
  • Educational estimate only. Not a substitute for professional clinical judgement, and must not be used to make treatment or dosing decisions.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Educational estimate only. Not a substitute for professional clinical judgement, and must not be used to make treatment or dosing decisions.

Frequently Asked Questions

Which drugs have a narrow index?

Warfarin, digoxin, lithium, phenytoin, theophylline and aminoglycosides are the classic examples.

Is a high index always safer?

It means dose-related toxicity is less likely, but idiosyncratic and allergic reactions are unrelated to the index.

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