Learning Objectives After completing this lesson, you will be able to: Define dose and explain its importance in determining toxicity . Analyze and compare dose-response curves . Describe the safety or toxicity of substances based on specific dose levels. In this section... Topics include: 2.1: Dose and It's Impact on Toxicity 2.2: The Dose Response Relationship 2.3: Dose Estimates of Toxic Effects 2.4: Determining the Safety of a Drug 2.5: NOAEL and LOAEL What We've Covered In this section, we explored the following main points: Dose is the amount of a substance administered; however, several parameters are required to characterize exposure to xenobiotics , including the: Number of doses Frequency of doses Total time period of exposure The dose-response relationship helps establish causality, or that the chemical induced the observed effects; the threshold effect, or the lowest dose that induced effects; and the slope, or the rate at which effects increase with dose increases. Estimating doses for toxic effects involves: Lethal Doses /Concentrations, such as LD0 , LD10 , and LC50 , which denote doses or concentrations that are expected to lead to death in specific percentages of a population. Effective Doses , such as ED50 and ED90, which denote doses that are effective in achieving a desired endpoint in specific percentages of a population. Toxic Doses , such as TD0 and TD50 , which denote doses that cause adverse toxic effects in specific percentages of a population. The Therapeutic Index ( TI ) compares the effective dose to the toxic dose of a drug. The Margin of Safety ( MOS ) compares the toxic dose to 1% of the population to the effective dose to 99% of the population. NOAEL is the highest dose at which there is no observed toxic effect. LOAEL is the lowest dose at which there is an observed toxic effect. Coming Up... In the next section, we will take a closer look at various types of toxic effects.