Therapeutic index

The therapeutic index of a medication is a comparison of the amount that causes the therapeutic effect to the amount that causes toxic effects. Quantitatively, it is the ratio of the dose required to produce the desired therapeutic effect and the toxic dose. A commonly used measure of therapeutic index is the effective dose of a drug for 50% of the population (ED50) divided by the lethal dose for 50% of the population (LD50).

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Generally, a drug with a narrow therapeutic index will have its dosage adjusted according to actual measurements of the blood levels achieved in the person taking it: examples of such drugs are digoxin and theophylline. This may be achieved through therapeutic drug monitoring (TDM) protocols.

Related Topics:
Digoxin - Theophylline - Therapeutic drug monitoring

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Drugs with a wider therapeutic index, such as diethyl ether and especially cannabis, require less expert intervention in their use, and tend to be less accepted in developed countries. Overdose is also related to the therapeutic index as well since with a narrow therapeutic index the transition into toxicity occurs more easily.

Related Topics:
Diethyl ether - Cannabis - Overdose

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