Biotransformation refers to the specific phase of “metabolism” during which one chemical is transformed to another by a biotic system, most often an enzyme. Metabolism includes various processes including absorption, distribution, excretion, and biotransformation. Several factors influence the site of action of a xenobiotic in a single cell or in an organism, namely, the dose to the cell, the rate of transport to the cell, and the duration of its effect. Biotransformation influences all of these processes by altering distribution characteristics as well as activity, and it, in turn, is influenced by the other processes.