In vitro activity: Itraconazole is metabolized into hydroxy-itraconazole (OH-ITZ), a known in vivo metabolite of ITZ, and two new metabolites: keto-itraconazole (keto-ITZ) and N-desalkyl-itraconazole (ND-ITZ). Itraconazole is a substrate for CYP3A in vitro and to characterize the metabolites generated. Itraconazole exhibits an unbound Km of 3.9 nM for CYP3A. Itraconazole metabolites are as potent as or more potent CYP3A4 inhibitors than ITZ itself. Itraconazole appears to act on the essential Hh pathway component Smoothened (SMO) by a mechanism distinct from that of cyclopamine and other known SMO antagonists, and prevents the ciliary accumulation of SMO normally caused by Hh stimulation. Itraconazole is active against 60 clinical isolates of Aspergillus spp. with geometric mean (GM) MICs of 0.25 mg/mL. Itraconazole acts primarily by impairing the synthesis of ergosterol, resulting in a defective fungal cell membrane with altered permeability and function. Itraconazole is effective for a wide variety of mycotic infections and some fungal meningeal infections. Itraconazole has an affinity for mammalian cytochrome P-450 enzymes as well as for fungal P-450-dependent enzyme, and thus has the potential for clinically important interactions (e.g., astemizole, terfenadine, rifampin, oral contraceptives, H2 receptor antagonists, warfarin, cyclosporine).