Cystic fibrosis (CF) is an inherited disorder which results in increased thickness of secretions, especially in the lungs. By adulthood, the majority of patients with CF will have a bacteria living in their lungs, called Pseudomonas aeruginosa which can cause lung infections. This usually results in worsening respiratory symptoms and often an acute deterioration in their lung function. They are usually treated with antibiotics that target the Pseudomonas aeruginosa. These antibiotics are typically given as short intravenous infusions several times a day. This study aims to compare the standard method of giving these antibiotics with a different strategy of giving these antibiotics to see if this can improve the outcomes of treatment of these infections and reduce the amount of Pseudomonas aeruginosa in the lungs of these patients. This strategy consists of giving the same antibiotics continuously, to ensure there is always enough antibiotic in the bloodstream and the lung to be able to kill the bacteria.

Inclusion Criteria:

1. Patients >= 18 years of age,

2. Pseudomonas aeruginosa isolated in sputum within the last 12 months,

3. has an acute infective exacerbation, defined by international standards of 2 or more of the following in the last 2 weeks:

   • change sputum volume or colour,
   • increased cough,
   • increased dyspnoea,
   • increased malaise, fatigue or lethargy,
   • anorexia or weight loss,
   • decrease in pulmonary function by 10% or more, or
   • new radiographic changes

Exclusion Criteria:

1. patients < 18 yrs of age,
2. patients that do not meet the criteria for an acute infective exacerbation,
3. concurrent pulmonary embolism, significant haemoptysis, pneumothorax, or respiratory failure,
4. impaired renal function with an estimated creatinine clearance < 60 mls/min,
5. patients allergic to ß-lactam antibiotics,
6. aminoglycoside contra-indicated,
7. intravenous antibiotics in the last 2 weeks, prior to this admission,
8. received more than 24 hours of intravenous antibiotics in this admission,
9. previous lung transplantation,
10. pregnancy or lactation, or
11. inability to consent.