Narrow therapeutic index (NTI) medications
Therapeutic index (TI) or therapeutic ratio
The ratio of the dose that produces toxicity to the dose needed to produce the desired therapeutic response. The following formula gives it.
TI = TD50/ED50,
TD50 is the toxic dose, and ED50 is the effective dose for 50% of the population tested.
The higher the Therapeutic Index, the safer the drug. However, drugs with a narrow TI, also known as NTI drugs or Narrow Therapeutic Range (NTR) drugs, need to be meticulously monitored. This is because the difference between their therapeutic and toxic doses is minimal.
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