Ketoconazole interacts with androgen receptors in a competitive fashion in intact human foreskin fibroblasts. Ketoconazole competes for [3H]dexamethasone binding to fibroblast glucocorticoid receptors with IC50 of 0.3 mM. [2] Ketoconazole reduces cell proliferation and [3H]thymidine incorporation with IC50 of 2.5 mM in the serum independent HT29-S-B6 colon cell clone. Ketoconazole inhibits the incorporation of [3H]thymidine with IC50 of 2 μM and 13 μM in the Evsa-T cell line and MDA-MB-231 cell line, respectively. Ketoconazole induces a decrease of the number of cells in S phase and a corresponding increase of the percentage of cells in Go-G1 in HT29-S-B6 cells. [3] Ketoconazole is susceptable to several Malassezia species with minimum inhibitory concentrations (MICs) of 0.03 µg/mL. [4]