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July 5, 1985

The LD50

Author Affiliations

Loyola University Stritch School of Medicine Maywood, Ill

JAMA. 1985;254(1):56. doi:10.1001/jama.1985.03360010062017

To the Editor.—  The median lethal dose (LD50) test is neither a tradition nor a ritual, as Dr Hubbard and Ms Young implied,1 but a scientific technique for assessing the toxic dose ranges of new drugs prior to their use in humans. Together with the median effective dose (ED50) test, it is used to determine a ratio yielding the therapeutic index (TI), ie, LD50/ED50=TI. Thus, the LD50 is not a number to be forgotten but rather a component of a ratio that serves as a guide for the selection of dosage regimens in human patients that predictably will be safe.Pharmacologists have a profound respect for life and must handle their experimental animals gently because only careful handling will generate accurate, reliable data as one moves from animal studies into phase I through III human studies. While major efforts are being made