Several protein kinase inhibitors have been reported to affect cytochrome P450 (CYP) 3A by time-dependent inhibition. Herein, we tested a set of six kinase inhibitors for time-dependent inhibition of CYP2C8 and CYP3A4 in human liver microsomes. Dovitinib, midostaurin and nintedanib exhibited an increased inhibition of CYP3A4 after a 30-min. pre-incubation with NADPH, as compared to no pre-incubation (IC shift >1.5). Masitinib, trametinib and vatalanib did not affect CYP2C8 or CYP3A4 by time-dependent inhibition (IC shift <1.5). The inhibitory mechanism of CYP3A4 by midostaurin and nintedanib, but not by dovitinib, was consistent with irreversible mechanism-based inhibition. The maximal inactivation rate (k ) and inhibitor concentration that supports half-maximal rate of inactivation (K ) values of midostaurin and nintedanib were 0.052 1/min. and 2.72 μM, and 0.025 1/min. and 17.3 μM, respectively. According to static predictions, inactivation of CYP3A4 by nintedanib was unlikely to cause drug-drug interactions with clinically used doses of nintedanib, whereas midostaurin was predicted to increase the plasma exposure to CYP3A4-dependent substrates several fold. Furthermore, based on reversible inhibition, masitinib and vatalanib were predicted to increase the plasma exposure to sensitive CYP2C8 and CYP3A4 substrates by ≥2-fold. In summary, our data identify midostaurin and nintedanib as time-dependent inhibitors of CYP3A4 and detect a risk of drug-drug interactions between vatalanib and CYP2C8 substrates, and between masitinib, midostaurin and vatalanib and CYP3A4 substrates. The liability of kinase inhibitors to affect CYP enzymes by time-dependent inhibition may have long-term consequences, in terms of drug-drug interactions and toxicities.