Many drugs commonly used in CF patients possibly inhibit CYP3A (e.g., importantly by azole antifungals such as itraconazole) or are metabolized by CYP3A (e.g., antibiotics, steroids, and hormonal contraceptives), and/or are substrates of P-gp (e.g., tacrolimus, ciclosporin, and digoxin) [27,53]. This evidence concerns the gene CYP3A4 and cystic fibrosis.