Early Methicillin-resistant Staphylococcus Aureus (MRSA) Therapy in Cystic Fibrosis (CF)

Inclusion Criteria: 1. Male or female ≥ 4 and ≤ 45 years of age at the Screening Visit. 2. Documentation of a CF diagnosis as evidenced by one or more clinical features consistent with the CF phenotype and one or more of the following criteria: * sweat chloride ≥ 60 mEq/liter by quantitative pilocarpine iontophoresis test (QPIT) * two well-characterized mutations in the cystic fibrosis transmembrane conductive regulator (CFTR) gene * Abnormal nasal potential difference (change in NPD in response to a low chloride solution and isoproteronol of less than -5 mV) 3. First OR early repeat MRSA colonization defined as: * First MRSA colonization: first documented isolation of MRSA from respiratory tract occurred ≤ 6 months prior to screening * OR Early repeat MRSA colonization: MRSA was previously isolated from the respiratory tract (≤ 2 times), but this was followed by at least 1 year of documented negative cultures for MRSA as noted below: \-- At least 2 cultures performed at least 3 months apart to document 1 year of culture negativity. Each of these cultures should be documented to have been collected at least 1 week after end of any antibiotic prescription with MRSA activity. Patient again recently positive for MRSA from the respiratory tract (within 6 months prior to screening) 4. Clinically stable with no significant changes in health status within the 14 days prior to screening 5. Written informed consent (and assent when applicable) obtained from subject or subject's legal representative and ability for subject to comply with the requirements of the study A repeat culture from the respiratory tract is obtained at screening but does not have to be positive to be able to enter the study. Exclusion Criteria: 1. Received antibiotics with activity against MRSA within 28 days prior to screening (see study manual for list of antibiotics) 2. Use of an investigational agent within 28 days prior to screening 3. For subjects ≥ 6 years of age: FEV1 at screening \< 30% of predicted for age based on the Wang (males \< 18 years, females \< 16 years) or Hankinson (males ≥ 18 years, females ≥ 16 years) standardized equations 4. MRSA from the screening culture resistant to rifampin OR resistant to both TMP/SMX and minocycline 5. History of intolerance to oral rifampin, or topical chlorhexidine or mupirocin 6. History of intolerance to both TMP/SMX and minocycline 7. \< 8 years of age and either allergic or intolerant to TMP/SMX or screening MRSA resistant to TMP/SMX 8. ≥ 8 years of age and allergic or intolerant to TMP/SMX and screening MRSA resistant to minocycline 9. ≥ 8 years of age and allergic or intolerant to minocycline and screening MRSA resistant to TMP/SMX 10. For females of child bearing potential: pregnant, breastfeeding, or unwilling to use barrier contraception through Day 15 of the study 11. Abnormal renal function at Screening, defined as estimated creatinine clearance \<50 mL/min using the Cockcroft-Gault equation 12. Abnormal liver function at the time of screening, defined as ≥2x upper limit of normal (ULN), of serum aspartate transaminase (AST) or serum alanine transaminase (ALT) 13. History of solid organ or hematological transplantation 14. Presence of a condition or abnormality that in the opinion of the Investigator would compromise the safety of the patient or the quality of the data.