to include children as young as 6 years old who have cystic fibrosis.
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The drug was approved in 2018 for patients aged 12 years and older who have the most common cause of the disease, two alleles for the F508del mutation in the gene that codes for the cystic fibrosis transmembrane conductance regulator (CFTR) protein, or at least one other CFTR mutation responsive to the combination, as listed in labeling.
The original approval was based on three phase 3, double blind, placebo-controlled trials, which demonstrated improvements in lung function and other key measures of the disease. One trial that found a 6.8% mean improvement in lung function testing over placebo at 8 weeks, and another that found a 4% improvement at 24 weeks, with fewer respiratory exacerbations and improved respiratory-related quality of life. A third trial in patients without the indicated genetic mutations was ended early for futility.
The efficacy in children under 12 years was extrapolated from those trials, plus an open-label study that found similar effects.
Labeling warns of elevated liver enzymes and cataracts in children, and notes that the drug should be taken with food that contains fat. Labeling also recommends against use with strong cytochrome P450 3A4 (CYP3A) inducers – rifampin, phenobarbital, St. John’s wort, among others – because they might reduce efficacy, and against use with CYP3A inhibitors – ketoconazole, clarithromycin, Seville oranges, grapefruit juice, etc. – because of the risk of increased exposure.
The most common side effects are headache, nausea, sinus congestion, and dizziness. The FDA has cleared a CF gene test to check for the required mutations. Symdeko is marketed by Vertex Pharmaceuticals.