Inclusion Criteria:

• Confirmed diagnosis of CF (sweat tests/genotype)
• The subject, or their legal guardian for children under 18 years old, must provide written informed consent.
• The subject must be in stable clinical condition at the time of and for a period of 14 days prior to their recruitment into the study.
• Age > 6 years old
• FEV1 > 40% predicted for height, age and gender
• Proven or anticipated compliance with therapy or study protocol
• Regular attendee at a Cystic Fibrosis Clinic (> 2 visits per year)
• Able to reproducibly perform lung function tests (spirometry)
• Relatively stable nutritional status (< 2 kg weight loss in last 6 months and < 5 kg weight loss in last year)
• Known to have “normal” (for CF subject) laboratory tests - haematology, biochemistry, immunology, coagulation, etc.

Exclusion Criteria:

• Requiring home oxygen (pO2 <55mmHg or pCO2 >50mmHg) or assisted ventilation.
• Considered “terminally ill” or listed for transplantation (either lung or liver). Subjects that are listed for transplant after being enrolled in the trial are eligible to continue in the trial.
• Subjects colonised with Burkholderia cepacia. However, if a subject becomes colonised with B. cepacia during the trial, they should continue in the trial. Subjects should be considered to be B. cepacia positive if they have had even a single lifetime isolate. In these subjects, spirometry should be measured on a dedicated spirometer.
• Cigarette smoker.
• Exposure to investigational drugs within the past 30 days.
• Major haemoptysis (> 60 mL in a single episode) within the last twelve months.
• Concurrent illnesses eg. cor pulmonale, clinically significant liver disease (portal hypertension, varices).
• Known allergy to quinine sulphate, Glucose 6-phosphate dehydrogenase deficiency.
• Immune thrombocytopaenic purpura.
• Pregnant or lactating females.
• At risk females unwilling to use appropriate contraception to prevent pregnancy for the duration of their enrolment in the study.