Abstract:
Metabolic reactions of xenobiotics, artificial compounds such as drugs, pesticides and food additives can be classified broadly into Phase I, asynthetic reactions of oxidation, reduction and hydrolysis; and Phase II, synthetic conjugation reactions. The metabolism of these compounds is often biphasic and can be expressed in the following form:
There are also a considerable number of compounds which can be metabolised only by one phase. These reactions frequently do not go to completion or are partially reversed so that although a compound may be metabolised by the general pattern shown, an animal may excrete three types of products, after the administration of the xenobiotic. These are (1) the original compound; (2) products of asynthetic reactions and (3) products of the synthetic or conjugation reactions. The nature and proportions of these three types of products vary from species to species partly because the enzymes involved in the reactions producing them vary from species to species.