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Safety and Efficacy of VX-828, Deutivacaftor, and Tezacaftor in Adults with Cystic Fibrosis

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What is this trial about?

A plain-language summary of the goals, design and what participants do

The study focuses on Cystic fibrosis, a genetic condition that affects the lungs and digestive system. Participants will receive an oral tablet that combines VX-828 with Deutivacaftor, and in some groups the drug will also include Tezacaftor. A standard medication containing Ivacaftor may be used as a reference treatment in the trial.

The purpose of the trial is to evaluate the safety and efficacy of the new combination therapy. Over a period of about four weeks, subjects will take the study medication once daily, while other participants receive a matching placebo. Safety will be monitored through reports of any side effects, regular blood tests, standard 12‑lead ECG recordings to check heart rhythm, and measurements of Sweat chloride levels, which reflect how the disease is affecting the body.

Effectiveness will be assessed by measuring lung function using the percent predicted forced expiratory volume in one second (ppFEV1) and by having participants complete a disease‑specific questionnaire that evaluates breathing symptoms (CFQ R). The study involves several clinic visits for these tests and for overall health checks.

The research process

The trial runs in 6 steps – from screening to follow-up. Each step says what happens and what the team monitors.

  1. Step 1

    Enrollment and baseline assessment

    After signing the informed consent, you attend the first study visit where baseline data are collected.

    Baseline procedures include a physical examination, blood tests, a 12‑lead electrocardiogram (ecg), measurement of vital signs, sweat chloride testing, lung function testing (percent predicted forced expiratory volume in 1 second, ppfev1), and completion of the cystic fibrosis questionnaire revised (cfq‑r) respiratory domain.

  2. Step 2

    Randomization and start of medication

    Based on a computer‑generated schedule, you are assigned to one of the study arms in a randomized, double‑blind manner; the specific medication you receive is unknown to you and to the study staff.

    If assigned to the test arm, you receive a vx‑828 tablet 20 mg and a deutivacaftor film‑coated tablet 250 mg taken orally each day; some participants also receive a tezacaftor tablet 100 mg daily.

    If assigned to the comparator arm, you receive either a fixed‑dose combination tablet containing tezacaftor 450 mg, elexacaftor 450 mg, and ivacaftor 450 mg or a kalydeco tablet 150 mg, taken orally each day.

    The tablets are taken once daily with water, preferably at the same time each day, for a total treatment period of 28 days.

  3. Step 3

    Daily medication administration

    Each morning you swallow the assigned tablet(s) with a glass of water.

    The dose is not altered during the 28‑day treatment period unless a safety concern arises, which would be addressed by the study physician.

    You keep a diary to record the date and time each dose is taken and any symptoms you experience.

  4. Step 4

    Mid‑study safety visit (day 14)

    On day 14 you return to the study site for a safety evaluation.

    The visit includes a brief physical examination, blood tests, an ecg, measurement of vital signs, and review of your symptom diary.

    The study staff also ask you to complete the respiratory domain of the cfq‑r again.

  5. Step 5

    End‑of‑treatment visit (day 28)

    On day 28 you attend the final study visit where the primary efficacy and safety assessments are repeated.

    Procedures include repeat sweat chloride testing, lung function testing (ppfev1), blood tests, an ecg, vital signs, and completion of the respiratory domain of the cfq‑r questionnaire.

    The study team also collect information about any adverse events (ae) that occurred during the treatment period.

  6. Step 6

    Study completion

    After the day‑28 visit, the study medication is stopped and you are advised not to start any new study drug.

    The study staff may provide a summary of your individual results and discuss any necessary follow‑up care.

Who can join the trial?

9 criteria

  • Weigh at least 35 kilograms (about 77 pounds).
  • Be able to give a proper sweat test at the first visit, and have a sweat chloride level of 30 mmol/L or higher. If the first sample is too small, one more sample may be taken.
  • Have a confirmed diagnosis of cystic fibrosis (CF) as decided by the study doctor.
  • Have the correct genetic makeup for the study:
    • For parts 1 and 2: carry one copy of the F508del mutation and a second CFTR gene that has a “minimal function” change that does not respond to the study drug.
    • For parts 3 and 4: carry two copies of the F508del mutation (called “homozygous”).
    • Show a lung function measurement called forced expiratory volume in 1 second (FEV1) that is at least 40 % of the normal value for your age, sex and height, measured according to standard testing rules.
    • Have stable CF disease as judged by the study doctor, meaning no recent major worsening.
    • Agree to stay on the same CF medicines and treatments throughout the study.
    • Be either male or female and fall within the age range allowed for the trial (generally children and adolescents).

Who cannot join the trial?

11 criteria

  • Any past illness or condition that could affect the study results or increase risk, such as liver disease with cirrhosis (severe scarring of the liver) or portal hypertension (high blood pressure in the vein that brings blood to the liver), organ transplants, alcohol or drug abuse in the last year, or cancer (except certain skin cancers and early‑stage cervical cancer that have not returned for at least five years).
  • Having taken part in another drug study that is still ongoing or was recent, unless a proper washout period (a break of at least 28 days or five drug half‑lives) has passed; simple observational studies are allowed.
  • Using medicines that are listed as prohibited medications within the time window before the first dose of the study drug.
  • Having a previous bad reaction to the study drug, such as past liver test problems that required stopping treatment or an allergy/hypersensitivity to the drug.
  • Having risk factors for a serious heart rhythm problem called Torsade de Pointes, including a family history of long QT syndrome (a heart electrical timing issue), low potassium levels (chronic hypokalemia), heart failure, thickened heart muscle (left ventricular hypertrophy), very slow heart rate (chronic bradycardia), past heart attack (myocardial infarction), heart muscle disease (cardiomyopathy), other heart rhythm problems (arrhythmias), recent serious brain bleeding or stroke (e.g., subarachnoid hemorrhage, intracranial hemorrhage, cerebrovascular accident), or nerve damage affecting automatic body functions (autonomic neuropathy).
  • Certain abnormal lab results at screening, such as total bilirubin (a waste product from the liver) that is 2 times higher than normal, liver enzymes AST, ALT, GGT or ALP that are 3 times higher than normal, low hemoglobin (less than 10 g/dL, a measure of blood’s ability to carry oxygen), or reduced kidney function measured by a glomerular filtration rate of 50 mL/min/1.73 m² or less.
  • Being pregnant, nursing, or planning to become pregnant during the study or within 90 days after the last dose (for women); or having a female partner who is pregnant, nursing, or planning pregnancy (for men). Participants must agree to use birth control as required.
  • Having an acute upper or lower respiratory infection, a lung flare‑up (called a pulmonary exacerbation), or recent changes in antibiotics for lung disease within 28 days before the first dose.
  • Having a lung infection with certain fast‑growing bacteria such as Burkholderia cenocepacia, Burkholderia dolosa, or Mycobacterium abscessus, unless you have had no positive cultures for these bugs in the past year and at least two negative cultures spaced at least three months apart, with the most recent one within six months.
  • Having an acute illness not related to cystic fibrosis, such as a stomach flu (gastroenteritis), within 14 days before the first dose.
  • Having a standard heart test (12‑lead ECG) that shows a QTcF interval longer than 450 milliseconds (a measure of the heart’s electrical recovery time) after up to three repeat tests.
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Investigated drugs

  • VX-445/VX-661/VX-770 film-coated fixed-dose combination tablet

    is a single pill that contains three medicines – tezacaftor, elexacaftor, and ivacaftor. These medicines work together to help the faulty protein in cystic fibrosis work more normally. In the study it is used as a reference treatment to compare the new drugs against.

  • VX-828 tablet

    is an experimental oral medication being tested in the trial. It is designed to improve the function of the cystic fibrosis protein, either by itself or when combined with other drugs such as tezacaftor and ivacaftor. The study looks at how safe it is and whether it helps patients feel better.

  • VX-561 film-coated tablet

    contains the experimental compound deutivacaftor. This medicine aims to correct the underlying protein problem in cystic fibrosis. In the trial it is examined alone and together with other agents to see if it is safe and effective.

  • Kalydeco film-coated tablets

    are a brand‑name product that contains ivacaftor. Ivacaftor is already approved for certain cystic fibrosis patients and helps the defective protein work better. In this study it serves as a standard treatment to compare the new drugs against.

  • VX-661 tablet

    is an experimental oral pill that provides tezacaftor. Tezacaftor helps the abnormal protein in cystic fibrosis function more correctly. The trial tests this medicine to see how it works alone or with other study drugs.

  • VX-121/VX-661/VX-561 film-coated tablet

    is a combination pill that includes tezacaftor, deutivacaftor, and vanzacaftor. All three components are intended to improve the performance of the cystic fibrosis protein. This product is used as another reference treatment to evaluate the safety and benefit of the new regimen.

What is already known about the treatment

  • Tezacaftor

    This medication is taken by mouth as a film‑coated tablet. It is an approved drug for cystic fibrosis and is well described in medical literature. It works by helping the faulty CFTR protein fold correctly and reach the cell surface, improving its function. It is classified as a CFTR corrector.

  • Elexacaftor

    Elexacaftor is administered orally in a film‑coated tablet form. It has received regulatory approval and is commonly referenced in CF treatment studies. It binds to a separate site on the CFTR protein, further increasing the amount of functional channel that reaches the cell surface. It belongs to the class of CFTR correctors.

  • Ivacaftor

    Ivacaftor is taken as an oral film‑coated tablet (brand name Kalydeco). It is an approved therapy for cystic fibrosis and is extensively documented in the literature. It acts as a CFTR potentiator, keeping the channel open longer so that chloride can pass through more efficiently. Its pharmacological class is CFTR potentiator.

  • Deutivacaftor

    Deutivacaftor is given orally as a film‑coated tablet. It is an investigational drug still under clinical study and not yet approved for general use. It functions as a potentiator of the CFTR channel, similar to ivacaftor, but its deuterium atoms give it a longer duration of action. It is classified as a CFTR potentiator.

  • Vanzacaftor

    Vanzacaftor is administered by mouth in a film‑coated tablet. It is an experimental CFTR corrector currently being evaluated in clinical trials and has not received regulatory approval. It helps the defective CFTR protein fold and move to the cell surface, increasing the number of working channels. It belongs to the class of CFTR correctors.

  • VX‑828

    VX‑828 is taken orally as a tablet. It is a novel, investigational compound that has not yet been approved and is being studied for cystic fibrosis treatment. It is designed to improve CFTR protein function, acting as a corrector that assists proper protein processing and trafficking. It is categorized as a CFTR corrector under development.

Investigated diseases

Cystic fibrosis - Cystic fibrosis is a genetic condition that causes the body to produce thick, sticky mucus. The mucus builds up in the lungs, making it harder to breathe and leading to repeated lung infections. Over time, the lung function can decline as the airways become damaged. The same thick mucus also blocks the ducts of the pancreas, which can interfere with the digestion of food. Digestive problems may cause poor weight gain and nutrient deficiencies. Symptoms often become more noticeable during childhood and can change as a person grows.
Trial detailsLast updated 7 Oct 2026
Age18+ yearsPhasePhase IITrial ID2025-523400-72-00Protocol codeVX25-828-101Estimated enrolment152 patientsSponsorVertex Pharmaceuticals Inc.

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