The Kinetics of Repeated-Dose Exposure

In repeated-dose exposures, chemicals have a chance to accumulate in the body. The level a chemical reaches in the body depends on how large and frequent the doses are as well as on the chemical s disposition in the body, i.e., its bioavailability, volume of distribution, and rate of elimination. The blood level of a chemical at any point in time in effect reflects a steady state between the amount of chemical that enters the body and the amount that leaves. The principle of mass balance (Section 2.8) can be used to estimate body burden  

Mass of chemical entering body = Mass of chemical exiting body (6.6) The mass balance can be expressed using kinetic parameters  

Amount in body = [(Dose/Dosing interval) x Bioavailability] x 1.44 x ti/2 (6.8) 

Equation (6.8) shows that increasing the dose and decreasing the dosing interval result in increased accumulation of a foreign chemical in the body. This jibes with common sense. Equation (6.8) shows that a chemical s half-life also has a profound 

Essentials of Toxic Chemical Risk Science and Society 

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