Inclusion Criteria:  Diagnosed with cystic fibrosis (genetic diagnosis and/or abnormal sweat test and clinical phenotype of lung disease) Age ≥ 8 yrs and < 18 yrs Body weight ≥20 kg Presence of Aspergillus infection as defined for this study Clinically stable condition without a significant change in lung function (FEV1 +/- 10%) or significant worsening of respiratory symptoms over the previous month Able to perform lung function test (FEV1%) Able to produce a sputum sample (spontaneous or induced sputum) Informed Consent given If female and of childbearing age must be using highly effective contraception (and must agree to continue for 7 days after the last dose of investigational medicinal product [IMP]  Exclusion Criteria:  Non-CF lung disorder Age < 8 yrs or ≥ 18 yrs Body weight < 20 kg Not able to perform lung function test (FEV1%) Unable to produce a sputum sample (spontaneous or induced sputum) Clinically unstable condition with significant change in lung function or significant worsening of respiratory symptoms Unable to tolerate oral medication Known hypersensitivity to itraconazole or posaconazole, or it's excipients. On active transplant list or transplant recipient Azole resistant Aspergillus sp. cultured Patients receiving terfenadine, ergot alkaloids, astemizole, cisapride, pimozide, halofantrine, quinidine, or HMG-CoA reductase inhibitors metabolised through CYP3A4 (eg. simvastatin, lovastatin, and atorvastatin) Patients receiving omalizumab Received systemic mould-active antifungals in the last month Shortened or elongated QT interval Cardiac failure ALT ≥ 200 U/L AST ≥ 225 U/L Alkaline phosphatase ≥ 460 U/L Bilirubin ≥ 50 umol/L eGFR < 20 ml/min/1.73 m2 (calculated with the Schwartz formula) Patients with known glucose-galactose malabsorption problems Pregnancy2 or breastfeeding Females of childbearing age who do not intend to use contraception measures. Informed Consent not given