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Another pharmacology question. LD50 of rats and humans

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Traumatic Acid:
Hi all
I've been looking online for a bit now but haven't really found a straight answer / have assignments I should be doing.

My question is weather or not when you find the LD50 of a drug for a rat, if we can assume that the LD50 will be similar for a human.

Probably for ethical reasons the LD50 of many drugs are unknown for humans ("And how much do you weigh again? Hmmmm, okay put this under your tongue please!") Yeah, can't see that going down to well. So how much info about human drug interactions can we tell from the LD50 response in a rat?

Cheers

Borek:
That's what we typically assume if there are no other data. It is never exactly accurate.

Yggdrasil:
Typically, the safe doses of drugs are determined in phase I clinical trials.  Human test subjects are given does of the drug at values very well below the LD50 determined in animal studies and monitored for side effects.  Doses are then increased until reaching the levels thought to be required for therapeutic efficacy.  Obviously, these human studies stop well short of determining lethal doses, but there is some threshold at which the severity of the side effects are judged to be unsafe.  However, this threshold would be different for different types of drugs (e.g. a blood pressure medicine taken every day vs a chemotherapy agent).

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