Toxicology of Industrial Compounds

and then multiply the animal clearance by the ratio of weight and MLP,
approximately 13 for the rat and 3.5 for a macaque monkey. Of course, as
shown by these data, there can be exceptions, and the monkey and indeed
the rat may not be a suitable species to undertake allometric scaling for all
compounds. However there is an increasing use of in vitro systems such as
isolated microsomes, hepatocytes or hepatic slices, to compare the
metabolic profiles of compounds in animals. If undertaken in conjunction
with allometric scaling, profound interspecies differences in the rates and
extent of metabolism compared to humans could be observed and provide
information on which is the most suitable species to use for scaling. Since
the allometric scaling for volume appears for most compounds to be
directly proportional to body weight with an exponent of approximately 1.
0, half-life can also be easily calculated thereby providing all the necessary
kinetic parameters to simulate plasma levels after repeated dosing in man.
With this information the absolute need to undertake kinetic analysis of
industrial chemicals in volunteers would be reduced since the exposure
calculated by this procedure is considerably better than that employed
presently using uncertainty factors, giving errors in excess of 1000 per
cent.
Further studies are of course needed to confirm these initial
observations, particularly with those chemicals used in industry or potential
environmental pollutants, but perhaps this re-evaluation shows that
allometry, when correctly used, may well have a practical role in the
evaluation of their potential risk to man.
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D.BRUCE CAMPBELL 55
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