Lethal dose (LD) is the quantity of a substance, toxin, radiation or infectious agent that causes death in a specified proportion of a test population. The most commonly reported metric is LD50, the dose that kills 50 % of exposed subjects.
Explanation
The concept of lethal dose originates in toxicology and pharmacology, where researchers determine how much of a compound is required to produce mortality in experimental animals. Doses are typically expressed in milligrams of substance per kilogram of body weight and vary with route of exposure (oral, inhalation, injection), species, age and health status. LD50 values are derived from dose–response experiments in which groups of animals are exposed to increasing amounts of a substance and mortality is recorded; statistical methods estimate the dose that kills half of the population. Other endpoints include LD10 or LD90. For gases and aerosols, lethal concentration (LC50) is used. In microbiology, lethal dose may refer to the number of virions, spores or cells required to kill a host; however, infectious dose (ID50) is more commonly used for pathogens that cause non fatal disease. Knowledge of LD values helps compare the acute toxicity of chemicals (e.g., cyanide vs. caffeine) and evaluate risks. Ethical concerns have led to reductions in animal testing and use of alternative methods such as in vitro assays and computational modelling. It is important to note that LD50 values determined in animals may not accurately predict human toxicity.
Reference values and considerations
• Botulinum neurotoxin has an estimated human LD50 of about 1 ng/kg when injected, making it one of the most potent toxins known.
• The oral LD50 of nicotine in rats is roughly 50 mg/kg, whereas the LD50 of caffeine is about 200 mg/kg.
• Median lethal doses are route dependent; cyanide is less lethal orally than intravenously because of first pass metabolism.
• For inhaled agents, LC50 values are reported as concentration (mg/m3) over a specified exposure time.
• Infectious doses such as ID50 for Vibrio cholerae or Shigella species measure the number of organisms required to cause illness rather than death.
Lethal dose metrics provide a standardized way to describe acute toxicity and compare hazards, but they must be interpreted cautiously with respect to species differences and ethical limitations.
Related Terms: LD50, toxicity, LC50, ID50, dose–response