how do they determine lethal doses of pharmaceutical drugs?

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I’ve just watched a documentary investigating a woman who died due to an unknown cause. It’s mentioned that she was on some medication, but the dose in her blood was lower than what is lethal. How do they check how much of a particular medicine it takes to kill a person without killing a person??

In: Biology

I believe they use something called LD50 (lethal dose 50), which is how much of a drug is considered a lethal dose to kill 50% of the population. This is tested on animals. So for example, if in a study of 30 rats, 5mg of a drug killed 15 of the rats, this would be the LD50. This amount is then adjusted for the average weight of humans. Let’s pretend that the average human weight is 100 times that of a rat, the LD50 for a rat would be 5mg, and the LD50 for humans would be 500mg.

Edit: changed 50mg to 500mg

Weight of a lab rat compared to the weight of the dose issued. Then compare that to the weight of the patient and the dose will be adjusted to be under that.

The data comes from experiments in rats and mice. But, there is also data for medicines that people commonly overdose on. There are thousands of people every year that intentionally take overdose on medicine for self harm, and that data can give you an idea of an LD50, based on how much those people were taking and how many of them died.