Study Evaluating Fosfomycin/Tobramycin for Inhalation in Cystic Fibrosis Patients With Pseudomonas Aeruginosa Lung Infection

Inclusion Criteria: * Males or females aged 18 years and older * Patients with CF as diagnosed by one of the following: * Documented sweat chloride greater than or equal to 60 mEq/L by quantitative pilocarpine iontophoresis test, OR * Documented sweat sodium greater than or equal to 60 mmol/L, OR * Abnormal nasal potential difference, OR * Two well-characterized genetic mutations in the CF transmembrane conductance regulator (CFTR) gene, AND * Accompanying symptoms characteristic of CF * Documented presence of PA in an expectorated sputum or throat swab culture at Visit 1 OR documented PA in 2 expectorated sputum or throat swab cultures within 12 months prior to Visit 1; one of the previous PA-positive cultures must be within 3 months prior to Visit 1 * Patients must be able to provide written informed consent prior to any study related procedures * FEV1 greater than or equal to 25% and less than or equal to 75% predicted at Visit 1 * Ability to perform reproducible pulmonary function tests * Chest radiograph at Visit 1 without significant acute findings (e.g., infiltrates \[lobar or diffuse interstitial\], pleural effusion, pneumothorax); or chest radiograph, CT, or MRI obtained within the 90 days prior to Visit 1 without acute findings or significant intercurrent illness; chronic, stable findings (e.g., chronic scarring or atelectasis) are allowed. Exclusion Criteria: * Current use of oral corticosteroids in doses exceeding the equivalent of 10 mg prednisone a day or 20 mg prednisone every other day * History of sputum or throat swab culture yielding B. cepacia in the previous 2 years * Current requirement for daily continuous oxygen supplementation or requirement for more than 2 L/minute at night * Administration of any investigational drug or device within 28 days of Visit 1 or within 6 half-lives of the investigational drug (whichever is longer) * Known local or systemic hypersensitivity to monobactam antibiotics * Known allergies/intolerance to tobramycin or other aminoglycosides * Known allergies/intolerance to fosfomycin * Inability to tolerate inhalation of a short acting beta2 agonist * Changes in or initiation of chronic azithromycin treatment within 14 days prior to Visit 1 * Administration of antipseudomonal antibiotics by inhalation, IV, or oral routes within the 14 days prior to Visit 1 * Changes in antimicrobial, bronchodilator (BD), corticosteroid, hypertonic saline, or dornase alfa medications within 7 days prior to Visit 1 * Changes in physiotherapy technique or schedule within 7 days prior to Visit 1 * History of lung transplantation * Abnormal renal or hepatic function or serum chemistry at Visit 1, defined as: * AST, ALT \> 3 times upper limit of normal range (ULN) * Creatinine \> 1.5 times ULN * Positive pregnancy test at Visit 1; all women of childbearing potential will be tested * Female patients of childbearing potential who are lactating or are not (in the opinion of the investigator) practicing an acceptable method of birth control; female patients who utilize hormonal contraceptives as a birth control method must have used the same method for at least 3 months before study dosing * Any serious or active medical or psychiatric illness, which in the opinion of the investigator, would interfere with patient treatment, assessment, or compliance with the protocol