The purpose of this study is to determine whether the nasal inhalation of Gernebcin® is effective to decrease the Pseudomonas aeruginosa bacterial count in the nasal lavage fluid.

Inclusion Criteria:

• subject has a confirmed diagnosis of cystic fibrosis
• detection of P. aeruginosa in nasal lavage (culture) with chronic P.a. colonization of the lung (from day -28)
• informed consent of the patients or parents
• subject is older than 7 years
• subject is able to comply with the inhalation procedures and nasal lavage procedures scheduled in the protocol
• women of childbearing potential are only included into the study, if they are using an effective method of birth control during the protocol

Exclusion Criteria:

• subject has a critical condition defined as: FEV1 < 30% and / or SaO2 < 93% without O2-substitution; need of O2-substitution
• subject had an ENT surgery within 3 months prior to study
• subject shows signs of nasal bleeding
• subject has an ear drum perforation
• subject had an acute rhinosinusitis or a pulmonary exacerbation at study entry with need of additional systemic antibiotic therapy against pseudomonas aerug.
• subject is unlikely to comply with the procedures scheduled in the protocol
• subject has a known allergic reaction to the medication
• subject is pregnant or breastfeeding
• subject participates in another clinical trial within 30 days prior to study entry or 30 days after end of the study.
• systemic (oral or intravenous) antibiotic treatment against P.a. 14 days prior to the inclusion and during the study
• if serum level of tobramycin is above 2 mg/l one hour after inhalation, subject has to withdraw the participation in the study.
• progressed renal insufficiency
• severe damage of the N. acusticus
• dizziness (potential damage of. N. vestibularis)