**4. Models for evaluation of drug metabolism**

In this chapter different *in vitro* and *in vivo* models for the evaluation of drug metabolism are presented. Advantages and disadvantages of subcellular fractions (microsomes, recombinant enzymes, cytosolic liver fractions, liver S9 fraction), cellular fractions (isolated hepatocytes, immortal cell lines, liver slices, perfused liver), *in vivo* animal and human studies will be presented.

Biotransformation occurs in liver, intestine, kidney, lungs, brain, nasal epithelium and skin. Since liver is the most important organ for drug metabolism [14, 15] the liver-based *in vitro* technologies for evaluation of drug metabolism are presented below. *In vitro* models that range from whole cell system to enzyme preparations are now increasingly applied for quantitative and qualitative assessment in preclinical drug development, post-approval routine checks, identification of metabolic determinant factors and prediction of drug-drug, herb-drug and food-drug interactions [15].
