SD Cystic Fibrosis Study

Inclusion Criteria: * Have Cystic Fibrosis * Male greater or equal to 18 years of age or female greater or equal to 16 years of age. * Must not be a smoker, or have smoked cigarettes or used other tobacco products regularly in the last 6 months * Must be clinically stable with no change in symptoms or medication, no admissions to hospital, no intravenous antibiotic therapy for at least 2 weeks before study start. * Able to perform lung function tests * Lung test reading with FEV1 \>40% predicted * Lung test with FEV1 has not changed by \>10% over past 12 months * Must have a normal ECG. * Women of child bearing potential must use an effective method of contraception. * Male subjects must agree to abstain from or use a condom during sexual intercourse or use a condom/spermicide, in addition to having their female partner use another form of contraception. * Aspartate aminotransferase (AST) and alanine aminotransferase (ALT) normal at study start. * Signed and dated written informed consent. * The parent/guardian must give written informed consent for the child to participate in this investigation. Adolescents must also sign the informed consent * The subject is able to understand and follow protocol. Exclusion Criteria: * Any clinically abnormality found at screening that is not part of the disease of cystic fibrosis. * any problem with pancrease * fatty feces * liver problems * sudden weight loss or poor nutritional status. * high blood pressure * infected with the hepatitis B, hepatitis C, or HIV virus * History of regular alcohol use * a current non-smoker * uses corticosteroids; regular use of high dose NSAIDs, within 2 months of study start. * have had positive Burkholderia cepacia, or MRSA within the last 12 months * on treatment for any mycobacterial infection * cannot be withdrawn from oral azithromycin during study * any marked bleeding haemoptysis in the last 12 months. * has taken more than 4 new chemical entities within the last year. * donate more than 500 mL within the last 56 day. * taken part in a drug trial in 30 days or taken part in a trial with a new chemical within the last 2 months. * on drugs that are CYP3A4, CYP2B6, CYP2C8 or OATP1B1 substrates with a narrow therapeutic index are excluded. * using non-prescription drugs, including, herbal and dietary supplements (including St John's Wort) within 7 days or unless permitted by the Investigator and sponsor * Consumption of grapefruit juice in last 7 seven day before study start. * Pregnant or breast feeding.