The inhaled drug that has served as the gold standard for clearing mucus in cystic fibrosis lungs is dornase alfa, sold under the brand name Pulmozyme. Approved decades ago and recommended by the Cystic Fibrosis Foundation for children aged six and older with mild-to-severe lung disease, this nebulized enzyme works by breaking apart the tangled strands of DNA released by dying white blood cells in the airways, reducing the thick, sticky mucus that defines the disease. For roughly 40,000 Americans and more than 105,000 people worldwide living with CF, that daily 2.5 mg inhaled dose has been a cornerstone of airway clearance therapy. But the landscape is shifting, and dornase alfa may soon share the stage with fundamentally different approaches.
A new generation of inhaled therapies is moving through clinical trials with the ambition of going beyond symptom management to address the root biology of CF mucus. Arcturus Therapeutics is testing ARCT-032, the first inhaled mRNA drug designed to deliver working copies of the CFTR protein directly to the lungs. Meanwhile, Enterprise Therapeutics is advancing ETD001, a long-acting inhaled blocker of the epithelial sodium channel that aims to rehydrate airway surfaces from the inside out. Neither is approved yet, and both carry the uncertainties that come with early-phase data. This article walks through what each of these therapies does, how their trial results stack up, and what the limitations are that patients and caregivers should understand before getting ahead of the science.
Table of Contents
- How Does an Inhaled Drug Clear Mucus in Cystic Fibrosis Lungs?
- ARCT-032 — Can Inhaled mRNA Fix the Root Cause of CF Mucus?
- ETD001 — A New Approach to Rehydrating CF Airways
- How Do These Inhaled Therapies Compare for CF Mucus Clearance?
- Limitations and Warnings About Emerging CF Inhalation Therapies
- The Role of Airway Imaging in Measuring Mucus Clearance
- What Comes Next for Inhaled CF Therapies
- Conclusion
- Frequently Asked Questions
How Does an Inhaled Drug Clear Mucus in Cystic Fibrosis Lungs?
To understand how inhaled mucus-clearing drugs work, you need to understand why CF mucus is so difficult to move in the first place. In healthy lungs, a thin layer of fluid coats the airways, and cilia — tiny hair-like structures — sweep mucus and trapped debris upward and out. In CF, a defective CFTR protein causes cells to absorb too much sodium and water from the airway surface, leaving behind mucus that is dehydrated, viscous, and prone to trapping bacteria. White blood cells rush to fight the resulting infections and then die, spilling their DNA into the mucus and making it even thicker. CF affects roughly 1 in 2,500 Caucasian live births, with incidence varying across ethnic backgrounds — about 1 in 13,500 Hispanic-Americans and 1 in 15,000 African-Americans. More than 75 percent of diagnoses happen before age two, and about 1,000 new cases are identified each year in the United States. Dornase alfa attacks this problem at the DNA level.
As a recombinant human DNase I enzyme, it cleaves the extracellular DNA strands that give CF mucus much of its gel-like rigidity. Once those strands are cut, the mucus becomes thinner and easier for the lungs to clear through coughing and chest physiotherapy. Clinical trials lasting from one month to two years have shown that dornase alfa improves FEV1, a key measure of how much air the lungs can force out in one second. In trials running six months or longer, it also reduced pulmonary exacerbations and lowered the risk of respiratory tract infections severe enough to require injectable antibiotics. It is not a cure, and it does not fix the underlying CFTR defect, but it has reliably kept lungs functioning better for longer in a disease where every percentage point of lung function matters. A second established option is inhaled hypertonic saline, typically at a 7 percent concentration, delivered twice daily. Rather than breaking down DNA, it works osmotically — drawing water into the airways to hydrate the mucus from the outside. The two therapies are often used together, though hypertonic saline can cause coughing and bronchospasm in some patients, and its effects on long-term lung function decline are more modest than those seen with dornase alfa.
ARCT-032 — Can Inhaled mRNA Fix the Root Cause of CF Mucus?
The most conceptually ambitious inhaled therapy in development is ARCT-032, an investigational mRNA drug from Arcturus Therapeutics. Unlike dornase alfa, which manages the downstream consequences of thick mucus, ARCT-032 is designed to deliver functional CFTR protein directly to lung cells by providing the mRNA instructions to produce it. If it works as intended, this approach would address the fundamental defect in CF rather than just thinning the mucus it produces. The first U.S. dosing of this inhaled mRNA therapy for CF was conducted at New York Medical College, marking a significant milestone for the technology. Phase 2 interim data released in October 2025 offered an early and incomplete picture.
After 28 days of inhaled 10 mg daily doses, four out of six participants with Class I CF mutations showed reductions in both mucus plug number and mucus volume on high-resolution CT scans, analyzed using FDA 501(k)-cleared AI imaging technology from Thirona. A post hoc exploratory analysis found an average absolute FEV1 increase of 3.8 percent and a relative increase of 5.1 percent among those four responders. However, these results come with significant caveats that deserve honest emphasis. The trial enrolled only six participants, making it impossible to draw firm conclusions about efficacy. The FEV1 improvements fall within the range of natural variability in lung function measurements, meaning they could reflect normal fluctuation rather than a true drug effect. The market appeared to agree with that cautious reading — Arcturus stock dropped on the announcement, and analysts described the data as “mixed.” The company has planned a 12-week safety and efficacy trial enrolling up to 20 CF participants in the first half of 2026, which should provide a somewhat clearer signal but still represents early-stage work. For families desperate for a breakthrough, it is worth remembering that promising Phase 2 signals fail to replicate in larger trials more often than not.
ETD001 — A New Approach to Rehydrating CF Airways
While ARCT-032 tries to replace the broken protein, ETD001 from Enterprise Therapeutics takes a different angle entirely. This inhaled drug blocks the epithelial sodium channel, known as ENaC, in airway cells. In CF, the defective CFTR protein fails to regulate ENaC properly, leading to excessive sodium absorption from the airway surface. Water follows the sodium, dehydrating the mucus layer. By blocking ENaC, ETD001 aims to keep more fluid on the airway surface, rehydrating the mucus so the lungs can clear it more effectively. ENaC blockers are not a new idea. Earlier attempts, including the well-known diuretic amiloride delivered by inhalation, failed largely because the drug was absorbed out of the lungs too quickly to maintain a therapeutic effect.
ETD001 was specifically engineered to overcome this limitation. Phase 1 results published in December 2025 tested doses ranging from 0.06 mg to 10.8 mg in 42 healthy volunteers. The drug was safe and well tolerated, with no serious adverse events, no treatment-related study withdrawals, and — critically for an ENaC blocker — no changes in blood potassium levels. The pharmacokinetic data showed slow absorption out of the lung, consistent with the prolonged retention needed for extended duration of action. ETD001 is currently being tested in a Phase 2 trial involving 28 days of treatment in CF patients, with headline data expected in early 2026. If the drug demonstrates meaningful mucus clearance and lung function improvement in actual CF patients, it could eventually complement or even partially replace existing hydration strategies like hypertonic saline. But Phase 1 safety in healthy volunteers does not guarantee efficacy in diseased lungs, and ENaC modulation has a long history of promising preclinical results that have not translated to clinical success.
How Do These Inhaled Therapies Compare for CF Mucus Clearance?
Choosing among inhaled mucus-clearing strategies involves understanding fundamentally different mechanisms and levels of evidence. Dornase alfa has decades of clinical use behind it, Cochrane-reviewed efficacy data, and Cystic Fibrosis Foundation guideline endorsement. It works for most CF patients regardless of their specific genetic mutation because it targets downstream mucus composition rather than the CFTR defect itself. The tradeoff is that it manages symptoms rather than addressing root causes, and it requires daily nebulization indefinitely. Hypertonic saline offers a low-cost, widely available alternative that works through simple osmotic hydration. It can be used alongside dornase alfa, and the Cystic Fibrosis Foundation recommends it as a mucus thinner.
Its limitations include tolerability issues — the saltiness can trigger coughing fits and airway irritation — and its effects on mucus clearance are generally considered more modest than those of dornase alfa. The experimental therapies represent potential paradigm shifts but carry proportional uncertainty. ARCT-032’s mRNA approach could theoretically benefit patients who cannot use CFTR modulators like Trikafta, particularly those with Class I nonsense mutations that current modulators cannot address. ETD001’s ENaC blockade could work regardless of mutation type, much like dornase alfa, but through a different mechanism. Earlier ENaC work by Spyryx Biosciences with SPX-101 showed some promise in the Phase 2 HOPE-1 trial, where the high dose of 120 mg twice daily produced a placebo-adjusted FEV1 increase of 5.2 percentage points in patients with baseline lung function between 40 and 80 percent predicted, though the result narrowly missed statistical significance with a p-value of 0.054 in a 46-patient study. The drug was well tolerated, with increased sputum production and cough being the most common side effects and no major potassium concerns. That earlier ENaC data provides some validation for the general approach, but ETD001 will need to demonstrate its own clinical proof.
Limitations and Warnings About Emerging CF Inhalation Therapies
The excitement around mRNA and ENaC-blocking inhalation therapies should be tempered by the reality of drug development timelines and failure rates. ARCT-032 has been tested in only six patients over 28 days. The imaging-based endpoints used to measure mucus reduction, while supported by FDA-cleared AI analysis, are not the same as the spirometry-based lung function endpoints that regulators typically require for approval. The FEV1 signals were described as exploratory and post hoc, meaning they were not the study’s primary planned analysis. The upcoming 12-week trial with up to 20 participants will help, but a definitive answer about whether inhaled mRNA can meaningfully and durably improve CF lung health is likely years away.
ETD001 faces its own set of challenges. The history of inhaled ENaC blockers is littered with failures, and while ETD001’s pharmacokinetic profile appears to address the rapid-absorption problem that doomed earlier drugs, Phase 2 data in CF patients will be the real test. Potassium safety is a particular concern with ENaC modulation because the channel plays a role in kidney electrolyte handling, though ETD001’s lung-targeted delivery and slow systemic absorption may mitigate this risk. The Phase 1 data showed no potassium changes in healthy volunteers, but patients with CF often have complex metabolic profiles that could respond differently. Patients and families should also be aware that even if these drugs succeed in trials, the path from positive Phase 2 data to an approved, accessible therapy typically takes several more years and hundreds of millions of dollars. In the meantime, established therapies like dornase alfa and hypertonic saline remain the evidence-based foundation of CF airway clearance, and skipping or reducing them in anticipation of future options would be a serious mistake.
The Role of Airway Imaging in Measuring Mucus Clearance
One notable development emerging from the ARCT-032 trial is the use of AI-powered imaging to measure mucus plugging. Arcturus used high-resolution CT scans analyzed by Thirona’s FDA 501(k)-cleared technology to quantify changes in mucus plug number and volume. This represents a shift from relying solely on spirometry, which measures airflow but cannot directly visualize where mucus is accumulating in the lungs.
For CF patients, this matters because FEV1 — while the traditional gold standard endpoint — can miss regional improvements in mucus clearance and may not change meaningfully in short trials or small populations. Imaging endpoints could eventually allow researchers to detect drug effects earlier and with fewer patients, accelerating the development of new therapies. However, these endpoints are not yet validated as surrogate markers for clinical outcomes by regulatory agencies, meaning a drug that clears mucus on a CT scan still needs to prove it keeps patients healthier and out of the hospital.
What Comes Next for Inhaled CF Therapies
The first half of 2026 is shaping up as a pivotal period for inhaled CF drug development. Arcturus plans to begin its expanded 12-week ARCT-032 trial, and Enterprise Therapeutics expects headline Phase 2 data from its ETD001 study in CF patients. Both readouts will help determine whether these novel mechanisms can deliver on their theoretical promise in actual clinical practice.
Looking further ahead, the convergence of mRNA delivery technology, improved understanding of airway biology, and AI-powered imaging tools suggests that the next decade could see inhaled CF therapies move well beyond the enzyme replacement and osmotic hydration approaches that have defined the field for a generation. For the more than 105,000 people worldwide living with CF, and particularly for those whose mutations make them ineligible for current CFTR modulators, these inhaled approaches represent not just incremental improvements in mucus management but potential new treatment categories. The key word, for now, remains “potential.”.
Conclusion
Dornase alfa remains the proven, guideline-recommended inhaled drug for clearing mucus in cystic fibrosis lungs, supported by decades of clinical evidence showing improvements in lung function and reductions in pulmonary exacerbations. Hypertonic saline provides an additional, complementary hydration approach. Together, these therapies form the current backbone of CF airway clearance and should not be abandoned or deprioritized based on early-phase experimental data.
The emerging therapies — ARCT-032’s inhaled mRNA approach and ETD001’s long-acting ENaC blockade — represent genuinely novel strategies that could expand treatment options for CF patients, particularly those underserved by existing CFTR modulators. But both are in early clinical stages with limited patient data, and the road from promising Phase 2 signals to approved therapies is long and uncertain. Patients and caregivers should stay informed, discuss trial participation with their CF care teams, and continue to rely on established treatments while the science matures.
Frequently Asked Questions
What is the main inhaled drug used to clear mucus in cystic fibrosis?
Dornase alfa (brand name Pulmozyme) is the primary inhaled drug for CF mucus clearance. It is a recombinant enzyme that breaks down DNA in airway secretions, reducing mucus thickness. The standard dose is 2.5 mg inhaled once daily via nebulizer, and it is recommended by the Cystic Fibrosis Foundation for patients aged six and older.
How does hypertonic saline help with CF mucus?
Inhaled hypertonic saline at 7 percent concentration works by drawing water into the airways through osmosis, hydrating the mucus so it becomes thinner and easier to clear. It is typically inhaled twice daily and can be used alongside dornase alfa. Some patients find it irritating to the airways, causing coughing or bronchospasm.
What is ARCT-032 and how is it different from current CF treatments?
ARCT-032 is an investigational inhaled mRNA therapy from Arcturus Therapeutics that delivers instructions for making functional CFTR protein directly to lung cells. Unlike dornase alfa, which thins existing mucus, ARCT-032 aims to fix the underlying protein defect that causes excessive mucus production. It has been tested in only six patients so far, and results are preliminary.
What happened in the ARCT-032 Phase 2 trial?
In October 2025, Arcturus reported that after 28 days of daily inhaled doses, four of six Class I CF participants showed reductions in mucus plug number and volume on CT scans. FEV1 improvements averaged 3.8 percent absolute increase in four patients, but this was within the range of normal variability and the sample was too small for firm conclusions. A larger 12-week trial is planned for the first half of 2026.
What is ETD001 and when will we know if it works?
ETD001 is an inhaled ENaC blocker from Enterprise Therapeutics that prevents excessive sodium and water absorption from airway surfaces, keeping mucus hydrated. Phase 1 testing in 42 healthy volunteers showed it was safe with no serious side effects and demonstrated prolonged lung retention. Phase 2 results in CF patients are expected in early 2026.
How many people have cystic fibrosis?
Approximately 40,000 children and adults live with CF in the United States, with an estimated 105,000 or more diagnosed across 94 countries worldwide. About 1,000 new cases are diagnosed annually in the U.S., and more than 75 percent of those diagnoses occur before age two.
