Susceptibility, adult-child differences

Whether differences in xenobiotic metabolism make the child more or less susceptible also depends on whether the relevant enzymes are involved in activation of the parent compound to its toxic form or in detoxification. There may also be differences in excretion, particularly in newborns who all have a low glomemlar filtration rate and have not developed efficient tubular secretion and resorption capacities (Altman and Dittmer 1974 NRC 1993 West et al. 1948). Children and adults may differ in their capacity to repair damage from chemical insults. Children also have a longer remaining lifetime in which to express damage from chemicals this potential is particularly relevant to cancer. 

The concept that infants and children may be a sensitive subgroup relates to their relative immaturity compared to adults. Children, as well as the unborn child, have in some cases appeared to be uniquely vulnerable to toxic effects of chemicals because periods of rapid growth and development render them more susceptible to some specific toxic effects when compared to adults. In addition to such toxicodynamic factors, differences in toxicokinetics may contribute to an increased susceptibility during these periods. It should be noted, however, that during the developmental and maturational periods the susceptibility to exposure to xenobiotics in children may be higher, equal, or even lower than in adults. Except for a few specific substances, not very much is known about whether and why the response to a substance may differ between age groups. It should also be borne in mind that, in terms of risk assessment, children are not simply small adults, but rather a unique population (Nielsen et al. 2001). 

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