Itraconazole is used to treat serious fungal or yeast infections. Itraconazole oral solution is only used to treat oropharyngeal or esophageal candidiasis (thrush, oral thrush). Itraconazole capsule is used to treat fungal infections, such as aspergillosis (fungal infection in the lungs), blastomycosis (Gilchrist’s disease), or histoplasmosis (Darling’s disease). Itraconazole capsule is also used to treat onychomycosis (fungal infection in the fingernails or toenails). Itraconazole is only used to treat onychomycosis of the toenails. This medicine works by killing the fungus or yeast and preventing its growth.