What is the importance of knowing the therapeutic index of a drug?

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It helps you to determine how much of the drug you need to take for it to be helpful and not harmful. It is a measure of the drugs margin of safety. Two numbers are obtained. The dose that produces desired effects in fifty percent of animals(if testing a drug on rats say) and the dose that produces toxic effects in fifty percent. The therapeutic index is the ratio of the two numbers. So if the toxic dose is five times higher than the effective dose then the index is 5.0. The lower it is the more care must be taken in prescribing the drug as the greater risk there is that an overdose will have tragic effects. If you don’t know this, then you haven’t taken pharmacokinetics or are in it now.It is the “margin of safety” that is found with a specific drug. Certain ones like digoxin have a narrower therapeutic index than say vitamin C.The importance of this is to know how closely you must monitor the blood dosage of the medicine.The therapeutic index is complicated by metabolism differences (fast/slow) and clearance differences (fast/slow clearance/conjugated clearance vs unconjugated etc..