Therapeutic index facts for kids

The therapeutic index is like a safety score for medicines. It helps doctors and scientists understand how safe a drug is to use. It shows the difference between a dose that helps people and a dose that could be harmful.

Therapeutic Index

The therapeutic index is a number that tells us how safe a medicine is. A higher number means the medicine is generally safer. A lower number means doctors need to be very careful when giving it. This is because there isn't much difference between a helpful dose and a harmful one.

What is the Therapeutic Index?

Imagine you have a medicine. You want it to help people, but you also want it to be safe. The therapeutic index helps measure this safety. It compares two main things:

• The amount of medicine that works for half the people.
• The amount of medicine that could cause serious harm or even be deadly for half the people.

Why is it Important?

Understanding the therapeutic index is super important for doctors and pharmacists. It helps them:

• Choose the right dose for patients.
• Know which medicines need very close monitoring.
• Develop new medicines that are both effective and safe.

For example, some medicines, like certain pain relievers, have a wide safety margin. This means you would need to take a lot more than the recommended dose for it to become dangerous. Other medicines, like some heart medications, have a very narrow margin. Even a slightly higher dose can be risky.

How is it Calculated?

The therapeutic index is found by dividing two important numbers. These numbers are usually found through careful studies:

• The first number is the dose that causes a helpful effect in half of the people tested. This is often called the "effective dose 50" (ED50).
• The second number is the dose that causes serious harm or is deadly for half of the people tested. This is often called the "lethal dose 50" (LD50) for animals, or "toxic dose 50" (TD50) for humans.

Understanding the Numbers

So, the formula looks like this: Therapeutic Index = (Dose that causes harm to 50% of people) / (Dose that helps 50% of people)

Let's say a medicine helps half the people at 10 milligrams (mg). But it causes serious harm to half the people at 100 mg. The therapeutic index would be 100 mg / 10 mg = 10. A higher number like 10 means there's a good gap between the helpful dose and the harmful dose. This makes the medicine safer to use. If the number was closer to 1 or 2, it would be much riskier.

Safe vs. Dangerous Doses

Medicines with a high therapeutic index are generally safer. Doctors have more room to adjust the dose without causing harm. For example, many common antibiotics have a high therapeutic index. Medicines with a low therapeutic index need very careful dosing. Doctors might start with a small dose and slowly increase it. They also might do blood tests to check the amount of medicine in a patient's body. This ensures the dose is helpful but not harmful. Some medicines used for cancer treatment or to prevent organ rejection after a transplant often have a low therapeutic index.

See also

In Spanish: Índice terapéutico para niños