Section 2: Dose and Dose Response

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:

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.