ABSTRACT
Normally a lipophilic xenobiotic that enters an animal’s body is rapidly detoxified. Detoxification can be divided into phase I (primary) and phase II (secondary) processes. Phase I consists of oxidation, hydrolysis, reduction and group transfer. The phase I metabolites are sometimes polar enough to be excreted, but are usually further converted by phase II reactions. In phase II reactions, the polar products are conjugated with a variety of endogenous compounds such as glucose, sulfate, phosphate, amino acids, or glutathione and subsequently excreted. Phase I reactions are usually responsible for decreasing biological activity of a toxicant and, therefore, the enzymes involved are rate limiting with respect to toxicity.
