Spironolactone with drug combination to improve health in adults with Fontan circulation (clinical trial)

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What is this study about?

The study focuses on adults who have a Fontan circulation, a condition that results from a special heart operation performed in childhood to allow blood to flow when only one functional pumping chamber is present. Over time, many individuals with this circulation develop problems such as fluid buildup and reduced ability of the heart to fill properly. The trial tests whether taking a combination of two medicines – Spironolactone, which helps the body eliminate excess fluid, and dapagliflozin, a drug that assists the kidneys in removing extra sugar and fluid – can improve these issues compared with a placebo.

The purpose of the study is to determine if the drug combination improves the way blood moves through the body in people with a Fontan circulation. Participants will receive either the active medicines or the placebo for a defined period and will attend regular clinic visits where simple tests are performed, including measurements of peripheral venous pressure (the pressure in the veins that indicates how much fluid is backing up) and pulmonary capillary wedge pressure (a reading that reflects the pressure inside the left side of the heart). Blood samples, basic exercise assessments, and safety checks such as blood chemistry will also be done to monitor how the body responds and to watch for any side effects.

1 randomization and start of study medication

after enrollment, a computer assigns the patient to either the active treatment group or the placebo group. the assignment is not known to the patient.

if assigned to the active group, the patient receives two oral tablets each day: one tablet of spironolactone 100 mg and one tablet of dapagliflozin (brand name for‑xiga) 10 mg. both tablets are taken once daily with water.

if assigned to the placebo group, the patient receives matching tablets that contain no active drug but are taken in the same way.

2 daily medication intake

the patient takes the assigned tablets every morning, preferably at the same time each day, for the entire period of study participation.

the tablets are swallowed whole; they are not broken, chewed, or dissolved.

the dose of spironolactone remains 100 mg per day and the dose of dapagliflozin remains 10 mg per day unless a safety assessment requires a temporary change.

3 regular clinic visits for safety monitoring

the patient attends a clinic visit approximately every four weeks. during each visit, blood is drawn to check serum potassium, creatinine, and other safety markers.

the study staff measures blood pressure, heart rate, and asks about any side effects or new health problems.

if any test result is outside the predefined safe range, the study doctor may adjust the medication schedule or pause treatment for a short period.

4 intravenous imaging with [al[18f]f]fapi‑74

at scheduled imaging visits (for example at the start of the trial and after six months), the patient receives an intravenous injection of the tracer [al[18f]f]fapi‑74.

the injection contains 310 megabecquerel (MBq) of the tracer, which is a very small amount of radioactivity used for a special type of PET scan that looks at heart tissue.

the scan takes about 30–60 minutes and helps researchers evaluate fibrosis (scarring) in the heart muscle.

5 functional and hemodynamic assessments

at baseline and at predefined follow‑up times, the patient performs a 6‑minute walk test, walking back and forth in a hallway for six minutes while the distance covered is recorded.

the patient also undergoes a cardiopulmonary exercise test (cpet) on a stationary bike or treadmill, which measures oxygen uptake, heart rate, blood pressure, and breathing efficiency during increasing levels of effort.

during these visits, doctors measure peripheral venous pressure (the pressure in a vein in the arm) and pulmonary capillary wedge pressure (an estimate of pressure inside the left side of the heart) while the patient is at rest and during peak exercise.

6 final study visit and end of treatment

at the last scheduled visit, usually near the end of the trial period, the patient repeats all safety blood tests, functional tests, and imaging procedures performed earlier.

the study medication (or placebo) is stopped after the final assessments are completed.

the patient receives a summary of the study results when they become publicly available, but no individual medical advice is given as part of the trial.

Who Can Join the Study?

Have already had a Fontan operation, which is a surgery used for people with a single working heart chamber called univentricular heart disease.
Show signs that the pressure in the veins returning blood to the heart is high, measured by a recent test. This includes any of the following: resting peripheral venous pressure (PVP) of 14 mmHg or more, PVP over 25 mmHg during exercise, a PVP‑to‑cardiac output slope greater than 3 mmHg per L/min, or currently taking medicines called diuretics that help remove extra fluid.
Have been medically stable (no hospital stays for problems with the Fontan circulation, irregular heartbeats (arrhythmia), or worsening heart failure) for at least three months before joining the study.
Have been on the same heart‑failure and blood‑thinning (anticoagulation) medicines for at least eight weeks before screening and plan to keep them unchanged during the trial, unless the study protocol requires a change.
Be able and willing to attend all study visits and follow all study procedures, such as special tests that change blood flow (preload modulation), blood draws, and a heart imaging scan called cardiac magnetic resonance (CMR), and to take the study medication as directed.
Provide a signed written informed consent (a document showing you understand the study and agree to take part) before any study procedures are done.
Be at least 18 years old at the time you sign the consent form.
If you are a woman who could become pregnant, agree to use birth control and follow the pregnancy‑testing rules required by the study.

Who Cannot Join the Study?

History of heart transplantation, mechanical circulatory support, or being on the waiting list for a new heart.
Unstable heart condition or worsening Fontan circulation within the past month, such as being hospitalized for heart failure, having a serious irregular heartbeat that needed treatment, or sudden decline in organ function.
Currently in the hospital or expected to be hospitalized soon because of Fontan circulatory failure.
Problems with kidney, liver, or potassium levels: blood potassium higher than 5.0 mmol/L, kidney function (eGFR) less than 30 mL/min/1.73 m² or no urine production, or liver enzymes or bilirubin more than twice the normal upper limit.
Low blood pressure with a systolic reading below 80 mmHg or feeling symptoms of low blood pressure (hypotension).
Ongoing acute illness such as appendicitis, COVID‑19, or stomach flu.
History of diabetic ketoacidosis or having type 1 diabetes.
Taking spironolactone, eplerenone, or SGLT2 inhibitor medicines now or within the last 8 weeks, unless they can be safely stopped before the study.
Having Addison’s disease or other significant adrenal gland problems.
Not able to understand the study information well enough to give personal informed consent.
Very high exercise capacity (peak VO₂ ≥ 35 mL/kg/min), which suggests the Fontan circulation is not limited.
Known allergy or strong reaction to the study drugs or any of their ingredients.
Having a pacemaker, implantable cardioverter‑defibrillator (ICD), or any device that cannot be scanned by cardiac MRI (CMR), or any other reason that makes MRI unsafe.
Difficulty placing an IV in the upper arm or known blockage in the veins that are part of the Glenn or Fontan connections or in the lung blood vessels.
Being pregnant, breastfeeding, planning to become pregnant during the study, or a woman who could become pregnant and cannot follow the required birth‑control rules.
Already taking part in another trial that uses an experimental drug or device.
Any medical, mental health, or social condition that the doctor believes could put the participant at risk, make it hard to follow the study, or affect the quality of the data.
Having had heart surgery or a heart‑related catheter procedure within the past 30 days, or planning such a procedure while in the study.

Where you can join this trial?

Verified and Recommended Sites

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Verified Sites

Site Name	City	Country	Status
Katholieke Universiteit te Leuven	Leuven	Belgium

Other Sites

No sites found in this category

Trial status

Country	Status	Recruitment Start
Belgium	Not yet recruiting	01.10.2026

Trial locations

Investigated Drugs:

Spironolactone is a pill taken by mouth that helps the body get rid of extra fluid and reduces the amount of salt it holds onto. In this trial it is being tested to see if it can lower the pressure in the veins and heart chambers of people who have a Fontan circulation, which may improve their overall heart function.

[AL[18F]F]FAPI-74 is a special injectable solution that contains a tiny amount of a radioactive tracer. It is used to create detailed images of the heart and blood vessels during a scan. In the study it helps researchers see how the heart and circulation are working and whether the other medicines are making any changes.

Dapagliflozin (also known as the brand name Forxiga) is an oral tablet that belongs to a group of drugs called SGLT2 inhibitors. It works by helping the kidneys remove more sugar and fluid from the body. In this trial it is combined with spironolactone to test whether together they can lower the pressure inside the heart and improve blood flow in people with a Fontan circulation.

Investigated Diseases:

Fontan procedure

Fontan circulation – Fontan circulation is a surgical arrangement used for people born with a single functional heart chamber. Blood from the body returns to the lungs without passing through a pumping chamber, relying on passive flow. Over time, this can lead to increased pressure in the veins and reduced filling of the heart. The heart may become stiff and less able to relax. The condition can cause a gradual decline in circulation efficiency as the patient ages.

Trial ID:

2025-524783-38-00

Trial Phase:

Therapeutic confirmatory (Phase III)

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Spironolactone with drug combination to improve health in adults with Fontan circulation (clinical trial)

What is this study about?

Who Can Join the Study?

Who Cannot Join the Study?