Abstract: The present invention relates to the use of N-[2,4-bis(1,1-dimethylethyl)-5-hydroxyphenyl]-1,4-dihydro-4-oxoquinoline-3-carboxamide (Compound 1), solids forms, and pharmaceutical compositions thereof for the treatment of CFTR-mediated diseases, particularly cystic fibrosis, in patients possessing specific genetic mutations. The present invention also relates to the use of Compound 1 in combination with 3-(6-(1-(2,2-difluorobenzo[d][1,3]dioxol-5-yl)cyclopropanecarboxamido)-3-methylpyridin-2-yl)benzoic acid (Compound 2), and Compound 1 in combination with (S)-1-(2,2-difluorobenzo[d][1,3]dioxol-5-yl)-N-(1-(2,3-dihydroxypropyl)-6-fluoro-2-(1-hydroxy-2-methylpropan-2-yl)-1H-indol-5-yl)cyclopropanecarboxamide (Compound 3), for the treatment of CFTR-mediated diseases, particularly cystic fibrosis, in patients possessing specific genetic mutations.