• Quantity per unit area of skin surface
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    The Dose-Response Relationship




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    tox exposure guidelines (1)

    The Dose-Response Relationship 
    In general, a given amount of a toxic agent will elicit a given type and intensity of response. The 
    dose-response relationship is a fundamental concept in toxicology and the basis for measurement 
    of the relative harmfulness of a chemical. A dose-response relationship is defined as a consistent 
    mathematical and biologically plausible correlation between the number of individuals 
    responding and a given dose over an exposure period.
     
    Dose Terms. In toxicology, studies of the dose given to test organisms is expressed in terms of 
    the quantity administered:
    • Quantity per unit mass (or weight). Usually expressed as milligram per kilogram of 
    body weight (mg/kg).
    • Quantity per unit area of skin surface. Usually expressed as milligram per square 
    centimeter (mg/cm
    2
    ).
    • Volume of substance in air per unit volume of air. Usually given as microliters of 
    vapor or gas per liter of air by volume (ppm). Particulates and gases are also given as 
    milligrams of material per cubic meter of air (mg/m
    3
    ).

    (Created 12/02) 
    UNL Environmental Health and Safety · (402) 472-4925 · http://ehs.unl.edu 
    The period of time over which a dose has been administered is generally specified. For example, 
    5 mg/kg/3 D is 5 milligrams of chemical per kilogram of the subject's body weight administered 
    over a period of three days. For dose to be meaningful it must be related to the effect it causes. 
    For example, 50 mg/kg of chemical "X" administered orally to female rats has no relevancy 
    unless the effect of the dose, say sterility in all test subjects, is reported.
     
    Dose-Response Curves. A dose-response relationship is represented by a dose-response curve. 
    The curve is generated by plotting the dose of the chemical versus the response in the test 
    population. There are a number of ways to present this data. One of the more common methods 
    for presenting the dose-response curve is shown in Graph 1. In this example, the dose is 
    expressed in "mg/kg" and depicted on the "x" axis. The response is expressed as a "cumulative 
    percentage" of animals in the test population that exhibits the specific health effect under study. 
    Values for "cumulative percentage" are indicated on the "y" axis of the graph. As the dose 
    increases, the percentage of the affected population increases.
    Dose-response curves provide valuable information regarding the potency of the compound. The 
    curves are also used to determine the dose-response terms that are discussed in the following 
    section.

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