Dose and Exposure Characterizations
SYSTEMIC, ORAL, INTRAVENOUS, AND INTRAPERITONEAL EXPOSURES
Systemic, oral, intravenous, and intraperitoneal exposures are commonly
expressed in terms of the weight of the agent (milligrams or micrograms) per
kilogram of the weight of the organism dosed.
Cutaneous exposures may be expressed in terms of a total dose or in terms of
the weight of the agent (milligrams or micrograms) per square centimeter times
the total area exposed.
The lethal dose (LD) for the organism in question is expressed in one of two
Incapacitation can vary from moderate (unable to see, breathless) to severe
Respiratory exposures are expressed in terms of the product of the
concentration (C) of the vapor or aerosol, usually expressed as milligrams (or
micrograms) per cubic meter (or liter), e.g., 35 mg-min/m3 or 0.13
µg-min/l, and the length of the exposure (T). The resulting value is
known as the CT.
Note that CT is an expression of exposure, not the amount inhaled or deposited.
The same CT can be produced by varying concentration or exposure time. The
effect of a given CT may or may not be the same if T is varied from a few
minutes to several hours. For example, a CT of 5 can be obtained by exposure
to 0.05 mg/m3 for 100 minutes or to 5 mg/m3 for 1 minute.
The generalization is not reliable for very short exposures (during which
breath might be held) or very long exposures (during which metabolic
detoxification may operate).
As above, certain key dosages are of interest:
- LCT50 is the CT required to produce 50-percent mortality in
the exposed population.
- ICT50 is the CT required to incapacitate 50 percent of the
These definitions are also used for vapor
or aerosol effects on the skin.