The caftor dose–response relationships with the usual CF disease parameters (i.e., sweat chloride concentration, FEV1, and BMI) show high variability in the treatment response, found even in patients with the same CFTR genotype and dosage regimen [14], suggesting that interindividual differences in PKs are likely to explain, at least in part, such inconsistency in drug responses [16]. The gene discussed is CFTR; the disease is cystic fibrosis.