A selective inhibitor of CYP3A4 (IC50 = 0.011 μM); highly selective for CYP3A4 over CYP3A5 (IC50 = 33 μM); inhibits metabolism of midazolam to 1'-hydroxy midazolam, testosterone to 6β-hydroxy testosterone, and vincristine to vincristine M1 in HLMs expressing CYP3A4 (IC50s = 9, 4, and 38 nM, respectively) but not those expressing CYP3A5; decreases lapatinib-induced quinoneimine-glutathione adduct formation in HLMs by 78% at 2.5 μM