Genetics xenobiotic-metabolizing enzymes affected

Various factors affect the activities of the enzymes metabolizing xenobiotics. The activities of these enzymes may differ substantially among species. Thus, for example, the possible toxicity or carcinogenicity of xenobiotics cannot be extrapolated freely from one species to another. There are significant differences in enzyme activities among individuals, many of which appear to be due to genetic factors. The activities of some of these enzymes vary according to age and sex. 

There are many factors, both chemical and biological, which affect the disposition of xenobiotics. Chemical factors include size and structure, pKa, chirality, and lipophilicity. Biological factors include species, sex and strain, genetic factors, hormonal influences, disease and pathological conditions, age, stress, diet, dose, enzyme induction and inhibition, and tissue and organ specificity. All of these factors can affect the toxicity of a chemical by changing its disposition, especially its metabolism. 

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