Therapeutic index

Definition

Therapeutic index (TI) is the ratio of the toxic dose to the therapeutic dose of a drug, indicating its safety margin. A higher TI means a greater margin between effective and toxic doses, making the drug safer.

5 Must Know Facts For Your Next Test

1. Therapeutic index is calculated as TD50/ED50, where TD50 is the dose causing toxicity in 50% of subjects and ED50 is the dose producing a therapeutic effect in 50% of subjects.
2. A drug with a narrow therapeutic index requires close monitoring to avoid toxicity.
3. Drugs with a wide therapeutic index are generally considered safer and can be administered with less risk of side effects.
4. The concept of therapeutic index helps in determining appropriate dosage ranges for medications.
5. Factors like age, liver function, and kidney function can influence an individual's response to drug dosages, potentially altering the therapeutic index.

Review Questions

• How is the therapeutic index calculated?
• Why is it important to monitor drugs with a narrow therapeutic index closely?
• What factors can affect an individual's response to drugs and alter their therapeutic index?

Related terms

Pharmacokinetics:

The study of how drugs move through the body including absorption, distribution, metabolism, and excretion.

Pharmacodynamics:

The study of how drugs affect the body and produce their effects.

Toxic Dose (TD): The dosage level at which a drug begins to produce harmful effects.