The purpose of this study is to evaluate the safety and tolerability of a new inhaled sodium-channel blocker called 552-02 in teens and adults with cystic fibrosis. 552-02 will be inhaled once a day for 14 days using a nebulizer. A small subgroup of patients will donate blood samples for pharmacokinetic analysis to see how 552-02 is absorbed into the blood and eliminated after 14 days of treatment.