Caution is advised in case of combination with CYP3A4 substrates having a narrow therapeutic margin i. e. immunosuppressive agents (cyclosporine, tacrolimus, sirolimus) as well as CYP3A4- metabolised cytotoxics, i. e. cyclophosphamide, etoposide, finasteride, ifosfamide, tamoxifen, vinca- alcaloids.