In cystic fibrosis, the airway gel-forming mucin MUC5B accumulates in the airways, preventing clearance of pathogens like Pseudomonas aeruginosa (PA). The CFTR-/- (KO) rat model exhibits a similar accumulation of Muc5b. Our lab has shown that increased Muc5b precipitates development of chronic PA infection. We hypothesized that reducing Muc5b in the KO rat airway would prevent occlusive mucus plugs and development of persistent PA infection. 6-month-old KO rats received Muc5b or scramble siRNA via intratracheal instillation. Rats were then inoculated with 106 colony forming units of mucoid P. aeruginosa isolate PAM57-15 and euthanized at 3- or 14-days post infection (dpi) to assess acute and persistent infection. At 14dpi, Muc5b siRNA treated KO rats had increased weight, decreased neutrophilic inflammation, and reduced mucus plugging in the small airways compared to scramble-treated KO and WT rats. These results indicate that pharmacologic intervention of Muc5b reduces mucus plugging during persistent PA infection.