Therapeutic index
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The therapeutic index (also known as therapeutic ratio or margin of safety), is a comparison of the amount of a therapeutic agent that causes the therapeutic effect to the amount that causes toxic effects. Quantitatively, it is the ratio given by the dose required to produce the toxic effect divided by the therapeutic dose. A commonly used measure of therapeutic index is the lethal dose of a drug for 50% of the population (LD50) divided by the effective dose for 50% of the population (ED50).
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Generally, a drug with a narrow therapeutic range (i.e. with little difference between toxic and therapeutic doses) may have its dosage adjusted according to measurements of the actual blood levels achieved in the person taking it. This may be achieved through therapeutic drug monitoring (TDM) protocols. Examples of drugs with a narrow therapeutic range, that may require drug monitoring both to achieve therapeutic levels and minimise toxicity, include: digoxin, dimercaprol, theophylline. Some antibiotics require monitoring primarily to minimise adverse effects, including: gentamicin, vancomycin, amphotericin B, and polymyxin B.
See also
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