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Pre-Clinical Testing → A Brief Introduction to Measures to Assess Drug Toxicity

Lethal dose (expressed as LD50, the estimated dose required to kill 50% of a group of experimental animals) has been largely abandoned as a useful measure of toxicity, and no longer needs to be measured for new compounds. Measures commonly used are:

  1. No observed adverse effect level (NOAEL), which is the largest dose causing neither observed tissue toxicity nor undesirable physiological effects, such as sedation, seizures or weight loss
  2. Maximum tolerated dose (MTD), which usually applies to long-term studies and represents the largest dose tested that caused no obvious signs of ill-health
  3. No observed effect level (NOEL), which represents the threshold for producing any observed pharmacological or toxic effect.

Additional readings:

  1. NOAEL: 10.1016/j.yrtph.2005.05.004
  2. MTD: 10.1016/j.toxrep.2015.02.011
  3. NOEL: 10.1007/978-3-642-79451-3_4