LD50 (mass per body weight) / LC50 (inhalation or aquatic concentration)
units
mg/kg (or μg/kg, ng/kg) of body weight
equation
Probit or logistic regression of mortality fraction against log10(dose)
pioneer
John William Trevan (introduced LD50 in 1927 to standardize biological assays of digitalis, insulin, and neoarsphenamine)
Core Principles & Analysis
Introduced in 1927 by British pharmacologist John William Trevan, LD50 standardized acute toxicity testing by determining the dose (typically in milligrams of substance per kilogram of body weight) lethal to 50% of test animals within a specified observation window.
LD50 values span more than nine orders of magnitude across substances — from water (>90,000 mg/kg orally in rats) and sodium chloride (~3,000 mg/kg) down to tetrodotoxin (~334 μg/kg orally / ~8 μg/kg parenterally in mice) and botulinum toxin (~1 ng/kg).
To reduce animal use under the 3Rs principles, OECD and regulatory agencies replaced classic multi-animal LD50 tests in 2002 with the Fixed Dose Procedure, Acute Toxic Class method, and Up-and-Down Procedure, as well as cell-based potency assays (approved by the FDA in 2011 for botulinum toxin testing).