Cystic fibrosis (CF) is a disease caused by changes in the gene that encodes the cystic fibrosis transmembrane conductance regulator protein (CFTR),1 found in the membrane of exocrine glands. Out of the more than 2000 CFTR variants known to date, the most frequent one is F508del, corresponding to the loss of an amino acid, phenylalanine, at position 508. The CFTR protein is responsible for chloride transport in the cell membrane, and changes in it result in changes in ion concentrations leading to dehydration of secretions in affected organs. The associated increase in morbidity and mortality is associated with the development of chronic obstructive pulmonary disease, which determines the prognosis and survival of individuals with CF.2

The recent introduction of CFTR modulators has been a considerable advance in the treatment of CF, achieving a substantial improvement in function in the abnormal protein.3–5 Ivacaftor (IVA), lumacaftor (LUM), tezacaftor (TEZ) and elexacaftor (ELE) are the molecules responsible for these striking changes.6 They are available as combinations in a single tablet as LUM/IVA, TEZ/IVA (dual combinations) or ELE/TEZ/IVA (ETI) (triple combination).6 The efficacy of the earlier combinations developed to treat patients homozygous for F508del (LUM/IVA o TEZ/IVA) was promising, but the outcomes were modest in clinical trials and real-world practice. However, the ETI combination, referred to as “triple therapy”, for treatment of patients carrying the F508del variant in at least one allele, has exhibited a significantly greater efficacy than its predecessors.7 Treatment with CFTR modulators decreases the frequency of respiratory exacerbations and improves lung function and quality of life in affected patients, drastically changing the course and prognosis of the disease.8–10 There is still a dearth of evidence on the changes in nutritional, anthropometric11 or gastrointestinal outcomes associated with the use of CFTR modulators, but a growing number of studies have found improvements in other aspects, such as a reduction in intestinal inflammation.

Fecal calprotectin (FC) is a biomarker of intestinal inflammation and its levels tend to be higher in patients with CF compared to healthy controls. This elevation may be due to chronic bowel inflammation resulting from the accumulation of thickened mucus, changes in the intestinal microbiota due to the use of antibiotics or to recurrent respiratory infections, among other possible causes. Multiple factors contribute to the elevation of FC in the context of CF, reflecting the complexity of this disease, which affects both the respiratory and the digestive systems.12,13

We conducted a prospective study in 15 pediatric cystic fibrosis reference units in Spain to assess changes in intestinal inflammation through the measurement of FC in patients with cystic fibrosis treated with LUM/IVA, TEZ/IVA and ETI at three time points: before treatment and at 6 and 12 months of treatment.

The sample included 117 patients, with a median age of 15.5 years (95% CI, 14.0–17.0) and ages ranging from 3.2 to 47.1 years, with no differences based on sex, all of whom carried the F508del variant in at least one allele (69% homozygous). Table 1 presents the demographic and baseline clinical characteristics of the sample. These characteristics were similar in the two groups under study with the exception of age, the genotype and the detection of Pseudomonas aeruginosa.

At baseline, the FC values ranged from 1 to 1450 μg/g (median, 49 μg/g; IQR, 23–108). When we analyzed baseline FC values in relation to different variables, we only found differences based on age using the nonparametric Mann-Whitney test (Fig. 1), with detection of higher values in the group aged more than 14 years. We did not find differences in relation to chronic treatment with azithromycin, colonization by Pseudomonas aeruginosa, exocrine pancreatic insufficiency or probiotic use. There were no differences in FC levels at baseline between the two treatment groups (LUM/IVA or TEZ/IVA, 48 μg/g [IQR, 26–91] vs ETI group 52 μg/g [IQR, 22–127]; P = .5677). We ought to highlight that at the start of the study, nearly half the patients (n = 57 [48%]) had FC values in the abnormal range (>50 μg/g) and 11% (all in the ETI group) had values greater than 250 μg/g indicative of intestinal inflammation.

Figure 1.

Fecal calprotectin levels by age group.

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In the total sample, we found a statistically significant decrease in FC levels at 6 and 12 months of treatment relative to baseline (Table 2). We also found a progressive reduction in the proportion of patients with FC levels greater than 50 μg/g relative to baseline: at 6 months, 48.7% compared to 33.1% (P = .0067), and at 12 months, 54% compared to 33.5% (P = .0218). We did not find significant differences between 6 and 12 months of treatment. In the ETI group, only two patients at 6 months and one patient at 12 months had FC levels greater than 250 μg/g (Fig. 2).

Figure 2.

Fecal calprotectin after double or triple modulator therapy.

LUM/TEZ + TEZ/IVA, lumacaftor/ivacaftor or tezacaftor/ivacaftor; ELE/TEZ/IVA, elexacaftor/tezacaftor/ivacaftor.

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The estimated change (95% CI) from treatment initiation to 12 months of treatment was greater in the ETI compared to the LUM/IVA or TEZ/IVA group, with a difference of −133 μg/g (−254 vs −13; P = .030). In the analysis adjusted for sex, probiotic use and isolation of Pseudomonas aeruginosa, the change was −130 μg/g (−259 vs −1; P = .049) (Fig. 2).

Pulmonary disease has been the main focus of clinical research on CF, since it is the factor most strongly associated with patient morbidity and mortality. The advent of CFTR modulators has been a significant therapeutic breakthrough, achieving significant improvements in lung function and a decrease in pulmonary exacerbations. However, few studies to date have described the changes in gastrointestinal health observed with these drugs, or, more specifically, analyzed potential improvements in intestinal inflammation by measuring FC levels.14–16

In our study, we analyzed a cohort of 117 patients with cystic fibrosis managed in 15 pediatric centers in Spain to describe observed changes in FC levels at 6 and 12 months of CFTR modulator therapy compared to baseline.

We found abnormal FC levels prior to treatment initiation in more than half of the patients, in agreement with previous studies,13,14 with higher levels in patients aged more than 14 years, a finding that could be related to the progression over time of chronic gastrointestinal and pulmonary inflammation and an altered intestinal microbiome, as reflected in the study conducted by De Freitas et al.12 We did not find an association with other factors, such as the use of probiotics, contrary to other authors that did find a decrease in FC with the use of certain probiotic strains.17,18 We also did not find a significant association with the presence of exocrine pancreatic insufficiency, contrary to the findings of the meta-analysis of Talebi et al.,19 who also described an association with lung function, body mass index and colonization by Pseudomonas aeruginosa. In this regard, our study did find a trend toward a positive association with colonization by Pseudomonas aeruginosa, although not statistically significant, possibly due to the smaller sample size in our study compared to the systematic review, so that FC may not only be a reliable noninvasive marker for the detection of gastrointestinal inflammation, but possibly also correlate to disease severity in patients with cystic fibrosis.

The anti-inflammatory effects at the level of the bowel already started to be described with the use of IVA as monotherapy, which was the first CFRT modulator authorized for treatment in patients with a class III genotype, in two case series that included 16 and 64 patients, respectively.20,21 Later on, following the marketing authorization of other CFTR modulators, a study assessed changes in intestinal inflammation following initiation of treatment with LUM/IVA in adolescents with cystic fibrosis followed up for one year. The median concentrations of FC decreased significantly after treatment initiation (102 μg/g [IQR, 69–210] vs713 μg/g [IQR 148–852]; P = .001).22 A recent open-label study assessed the effect of LUM/IVA in 44 children aged 1–2 years, finding a reduction in FC of –106 mg/kg at 24 weeks,23 the youngest population treated to date. However, an even more recent trial with TEZ/IVA with measurement of FC, assessment of changes in the intestinal microbiome and use of gut symptom questionnaires did not find significant differences, as was the case in our study.24

A salient finding in our study was the statistically significant difference in the decrease in FC levels when we compared treatment with dual combinations (LUM/IVA or TEZ/IVA) versus triple therapy with ETI, with the latter achieving a greater reduction in FC at both 6 and 12 months (−133). The results of triple therapy observed in our study were even better than those obtained in PROMISE, a prospective study conducted in 56 centers that found a mean difference of −66.2 μg/g (95% CI, −86.1 to −46.2) at 6 months of treatment in patients aged more than 12 years,25 and other pediatric studies, like the one conducted by Reasoner et al.,26 who found a mean decrease of −64 μg/g at 12 months (95% CI, −16 to −112).26 To date, ours is the only study that has assessed the improvement in FC levels following treatment with ETI compared to other CFTR modulator therapies, such as LUM/IVA or TEX/IVA.

There are limitations to our study, given its observational nature and the lack of randomization. However, it must be taken into account that the safety and efficacy of CFTR modulator therapy has already been proven in clinical trials, so it would be unethical to undertake a randomized study or to deny patients with eligible variants access to these drugs. On the other hand, the fact that the measurement of FC levels was not centralized may have affected the precision of the calculated magnitude of the changes. In order to minimize the impact of these limitations, we proposed comparing the results in patients treated with a dual versus triple combination in the study protocol, as well as adjusting results for factors known to affect intestinal inflammation in the statistical analysis, such as the use of probiotics or the isolation of Pseudomonas aeruginosa. We also assessed changes in FC in terms of the estimated change in each patient, as there could be differences based on the laboratory that conducted the tests.

Among the strengths of our study, we ought to highlight the prospective and multicenter design, in addition to being the largest case series published to date and the first study in Spain to assess the effectiveness of these drugs in reducing intestinal inflammation in real-world practice.

The use of ETI was associated with a significant reduction in FC levels compared to dual-combination therapy with LUM/IVA or TEZ/IVA, demonstrating that triple therapy is not only effective in improving respiratory parameters, but also gastrointestinal parameters such as intestinal inflammation.

This research did not receive any external funding.

The supplemental content for this article can be consulted in its online version, available at doi:10.1016/j.anpedi.2025.503836.