Supratherapeutic, as opposed to clinically relevant, con-centrations of inhibitors and substrates may be utilized. In addition, experimental condi-tions such as enzyme protein concentration and buffers can critically affect specific resultsand confound in vitro/in vivo correlations. To account for variability in individual enzyme expression, positive controls for inhibition and induction should alwaysbe used .The following briefly summarizes the strengths and weaknesses of currently available in vitro human methodologies for assessing CYP drug interactions and predictingtheir clinical significance.