The propose of this study to conduct a proof of concept clinical trial to test if administration of losartan augments CFTR function in vivo in patients who are on Orkambi™. The goal of this pilot clinical trial is to examine the ability of losartan on CFTR (primary hypothesis) and possibly BK rescue/augmentation (secondary hypothesis) in patients homozygous for F508del on Orkambi™ therapy. The additional benefit for Large, Ca 2+ - and voltage-activated K + channels (BK) channels could be important, but is harder to measure in vivo. Towards this end, however, the study will assess calcium-activated chloride channel (CaCC)/BK activity together as the response to adenosine triphosphate (ATP) during nasal potential difference (NPD) measurements, even though this is not an accurate reflection of either channel on its own.