Effects of Sildenafil on CFTR-dependent Ion Transport Activity
Condition: Cystic Fibrosis
MeSH terms: Cystic Fibrosis; Fibrosis
Intervention: Sildenafil; Placebo
Intervention description: During the course of the study, patients will receive 4 weeks of therapy: 28 days of placebo orally t.i.d. or 28 days of days of sildenafil orally t.i.d. Dosing of sildenafil will be escalated after the first week (20 mg orally t.i.d for the first week, then subjects will take 40 mg orally t.i.d. for 3 weeks). Patients not tolerating dose escalation will be discontinued from the study.; Patients receiving placebo will have sham dose escalation to maintain blinding.
Intervention MeSH terms: Sildenafil Citrate
Phase: Phase 2
Study type: Interventional
Primary purpose: Treatment
Allocation: Randomized
Intervention model: Parallel Assignment
Masking: Quadruple (Participant, Care Provider, Investigator, Outcomes Assessor)
Enrollment: 19.0
Sex: All
Minimum age: 18 Years
Healthy volunteers: No
Keywords: Cystic fibrosis; CFTR; Phosphodiesterase inhibitor; Nasal potential difference; Sweat test

Summary:

      Dehydrated airway surfaces resulting from sodium hyperabsorption and lack of chloride
      secretion are critical to the pathology that leads to the morbidity and mortality from Cystic
      Fibrosis (CF) lung disease. Previously published work in CF cell lines has demonstrated that
      by increasing cGMP and restoring inhibition of ENaC, sodium hyperabsorption may be reversed
      following administration of a phosphodiesterase inhibitor (PDEi,) such as sildenafil.
      Additionally it has been shown in CF cell lines and animal models, that phosphodiesterase
      inhibitors/analogues can enhance chloride secretion and/or correct surface localization of
      ΔF508 CFTR. The goal of this project is to translate the results of this work from the
      laboratory into a clinical trial in patients with CF using an FDA-approved therapy. The
      Specific Aims of this project are to: 1) Evaluate the effect of systemically administered
      phosphodiesterase inhibitors on ion transport in CF by measurement of Na+ and Cl- conductance
      by NPD and Na+ and Cl- concentration in sweat utilizing pilocarpine iontophoresis 2) To
      establish appropriate dosing of sildenafil in CF by performing a dose-escalation study during
      which patients are carefully monitored for side effects, plasma sildenafil levels are
      obtained and outcome measures are compared based on the dose of sildenafil administered. The
      results of this study in conjunction with those from an ongoing study examining the role of
      sildenafil as an anti-inflammatory in CF will aid in establishing safety, pharmacokinetics
      and mechanism of action of sildenafil in the treatment of CF lung disease.
    

Eligibility criteria:

        Inclusion Criteria:

          1. Confirmed diagnosis of CF based on the following criteria: Positive sweat chloride
             ≥60mEq/liter (by pilocarpine iontophoresis) and genotype with two F508del CFTR
             mutations, and accompanied by one or more clinical features consistent with the CF
             phenotype

          2. Male or female subjects ≥ 18 years of age

          3. FEV1 ≥ 50% predicted (Hankinson)

          4. Clinically stable without evidence of acute upper or lower respiratory tract infection
             or current pulmonary exacerbation within the 14 days prior to the screening visit

          5. Ability to reproducibly perform spirometry (according to ATS criteria)

          6. Ability to understand and sign a written informed consent or assent and comply with
             the requirements of the study

          7. Willing and able to perform nasal potential difference testing

          8. No changes in use of nasal medications within 2 weeks of screening visit

          9. If on Orkambi, has been on stable Orkambi dose for at least 4 weeks at day 1.

        Exclusion Criteria:

          1. History of hypersensitivity to sildenafil

          2. Use of an investigational agent within the 4-week period prior to Visit 1 (Day 0)

          3. Breastfeeding, pregnant, or verbal expression of unwillingness to practice an
             acceptable birth control method (abstinence, hormonal or barrier methods, partner
             sterilization or intrauterine device) during participation in the study

          4. History of significant hepatic (SGOT or SGPT > 3 times the upper limit of normal at
             screening, documented biliary cirrhosis, or portal hypertension), cardiovascular
             (history of aortic stenosis, coronary artery disease, pulmonary hypertension with
             right ventricular systolic pressure >55 mmHg or life-threatening arrhythmia),
             neurological (history of stroke), hematologic (history of bleeding diathesis),
             ophthalmologic (history of retinal impairment or non-arteritic ischemic optic
             neuritis) or renal impairment (creatinine >1.8 mg/dL.)

          5. Inability to swallow pills

          6. Previous lung transplantation

          7. Use of concomitant nitrates, α-blocker, or Ca channel blocker

          8. Use of concomitant medications known to be potent inhibitors of CYP3A4 (e.g.
             ketoconazole, itraconazole, ritonavir, clarithromycin, erythromycin, rifampin,
             verapamil)

          9. Presence of a condition or abnormality that in the opinion of the investigator would
             compromise the safety of the subject or the quality of the data

         10. Weight less than 40 kg

         11. History of sputum or throat swab culture yielding Burkholderia cepacia within 2 years
             of screening

         12. History of nasal disease or nasal surgery that would, in the opinion of the
             investigator, impede accurate measurements of NPD

         13. Use of anticoagulant medication (e.g. heparin, coumadin)

         14. Resting room air oxygen saturation <93%

         15. Use of nighttime oxygen

        15) History of migraine headaches 16) Baseline BP of < 90/50 mm Hg