Table 1:

Assay systems to predict metabolic clearance

	Metabolic competency	Longevity	Barrier function	Physiological relevance	Costs	Throughput/ease of use
Isolated Perfused Organs	XXXX	X	XXXX	XXXX	XXXX	X
Tissue Slices	XXX	X	X	XXX	XXXX	X
Primary Cells (immediately isolated or cryopreserved from tissues)	XXX	X	X	X	XX	XXXX
Primary Cells in Culture	XX	XX	XXX	XXX	XX	XX
Differentiated Cell Lines (with barrier function)	N/A	N/A	XXX	N/A	X	XXX
Immortalized Cell Lines	X	XXXX	X	X	X	XXXX
Subcellular Fractions (i.e., Microsomes/S9)	XXX	X	N/A	X	X	XXXX
Recombinant Enzymes	XX	X	N/A	X	X	XXXX

Table cell contents represent a continuum of relevant characteristics, with “X” indicating low or minimal and “XXXX” indicating high or extensive. Use of each test system for a particular application should be considered within the context of the goals of the experiment.