[Tryptamine]

I was told that the LD50 of a particular substance when ingested was 280mg/kg

Does that mean the amount someone would have to consume would be 280mgs?

[Narumi]

mg/kg doses refer to a particular dosage dependent on the mass of the person in question. So if a substance is recommended at 280mg/kg, and the subject is 70kg, the dose would be 19.6g. Does that make sense?

[Tryptamine]

Ahh I think I understand, basically kg = How much the person weighs.. so with your example at 70kg, you'd divide 280 by 70 (280/70) giving you 19.6 grams?

[Borek]

Nope. You need 280 mg per kilogram of body mass. Start chopping the body into 1 kg chunks, then put 280 mg of substance on each chunk - you have used correct amount of substance. Now, can you calculate how much you used?

[Arkcon]

Note, LD50 means 50% of test subjects (generally mice, or rabbits) are affected (usually, but not always, dying), after this dosage.  If you watch enough crappy TV movies, you'll realize that most humans search for a greater than 50:50 chance at dying in all their endeavors.  The whole point of the LD50 number is to give people a quantifiable number to link to the hazard.

Example:

Colchicine has a intravenous-mouse LD50 of 1.6 mg/kg, while triethylamine has a skin-rabbit LD50 of 570 mg/kg .  Those numbers are meant to give you a guideline to handling.  I was always very careful when working with colchicine, but my first encounter with the LD50 was with when I spilled TEA on myself.  After looking up the LD50, and doing the math, I realized I'd have to fall into vat to be seriously injured, but I still had to be careful with spills.