Finerenone Cuts Proteinuria in Type 1 Diabetes Kidney Disease Trial, but Long-Term Benefit Unproven

For the first time in more than a generation, a drug has been shown in a large clinical trial to improve a key marker of kidney damage in people with type 1 diabetes—a group that faces high risks of kidney failure with few treatment options beyond blood sugar and blood pressure control.

In a study published March 5 in The New England Journal of Medicine, researchers reported that finerenone significantly reduced protein in the urine (albuminuria), a marker of kidney injury, in adults with type 1 diabetes and chronic kidney disease (CKD) when added to standard care over six months.

The trial, known as FINE-ONE, was not designed to show whether finerenone prevents dialysis, kidney transplant, or death in this population. Still, it represents the first modern phase 3 kidney trial to post a positive result in type 1 diabetes and relies on a lab measure that regulators and specialists already use in type 2 diabetes.

“In this trial involving adults with type 1 diabetes and CKD, finerenone resulted in a significantly greater decrease in the urinary albumin-to-creatinine ratio than placebo over 6 months of treatment,” the investigators wrote.

What the trial found

Researchers enrolled 242 adults (18 and older) with type 1 diabetes and CKD at more than 80 sites in nine countries. All participants were receiving standard kidney-protective therapy, including a stable dose of either an angiotensin-converting enzyme (ACE) inhibitor or an angiotensin receptor blocker (ARB)—treatments that have anchored diabetic kidney care since the 1990s.

To qualify, patients needed:

• An estimated glomerular filtration rate (eGFR) between 25 and <90 mL/min/1.73 m², and
• Significant albuminuria, with a urinary albumin-to-creatinine ratio (UACR) of at least 200 mg/g.

The trial excluded people with type 2 diabetes, symptomatic heart failure requiring traditional mineralocorticoid receptor antagonists, or recent use of SGLT2 inhibitors or GLP-1 receptor agonists.

Participants were randomly assigned to once-daily finerenone (10 mg or 20 mg depending on kidney function) or placebo, on top of their usual medications, for six months, followed by a washout and follow-up period.

Albuminuria: the primary endpoint

At baseline, median UACR was 574.6 mg/g in the finerenone group and 506.4 mg/g in the placebo group. After six months:

• Median UACR fell to 373.5 mg/g with finerenone
• Median UACR was 475.6 mg/g with placebo

That translated into a 34% reduction in UACR from baseline in the finerenone group versus 12% in the placebo group. Overall, finerenone produced a 25% greater reduction in albuminuria than placebo, a statistically significant difference.

Depending on the analysis, roughly half to two-thirds of patients taking finerenone achieved at least a 30% drop in UACR, compared with about one-third to one-half of those taking placebo.

eGFR changes

Kidney filtration (eGFR) declined more during treatment in the finerenone group—by 5.6 mL/min/1.73 m², compared with 2.7 in the placebo group—but the difference largely disappeared during washout. Investigators and editorialists described this as consistent with a hemodynamic (blood flow–related) effect seen with other kidney-protective therapies, rather than ongoing structural damage.

Safety and side effects

Overall adverse events were similar in both groups:

• 47.1% in the finerenone group
• 49.2% in the placebo group

Serious adverse events occurred in about 12% of participants in each arm.

The primary safety concern was hyperkalemia (high blood potassium), a known risk with finerenone and related drugs. Hyperkalemia occurred in:

• 10.1% of patients on finerenone
• 3.3% of patients on placebo

Two patients (1.7%) in the finerenone group discontinued the study drug due to elevated potassium.

Bayer, which developed finerenone and funded the trial, said the safety profile aligned with prior finerenone studies.

A long-standing gap in type 1 diabetes care

Epidemiologic studies suggest roughly 30% of people with type 1 diabetes develop CKD, and about one in four of those may progress to kidney failure. Kidney disease is a leading contributor to mortality in type 1 diabetes, due to both kidney failure and associated cardiovascular complications.

Yet many therapies that have reshaped kidney care in type 2 diabetes—including SGLT2 inhibitors, GLP-1 receptor agonists, and finerenone—have not been tested in large, dedicated outcomes trials in type 1 diabetes. Regulatory approvals and major guideline recommendations, including those from Kidney Disease: Improving Global Outcomes (KDIGO) and the American Diabetes Association, therefore focus on type 2 diabetes.

Hiddo Lambers Heerspink, a nephrologist at University Medical Center Groningen in the Netherlands and chair of the FINE-ONE study, called the results a “landmark moment” in a Bayer news release, citing limited options for patients with type 1 diabetes and CKD.

What finerenone is—and what it is not yet

Finerenone (marketed as Kerendia) is a nonsteroidal mineralocorticoid receptor antagonist. By blocking a hormonal pathway implicated in inflammation and fibrosis in the kidneys and heart, it is intended to slow organ damage.

In July 2021, the U.S. Food and Drug Administration approved finerenone to reduce the risk of sustained kidney function decline, kidney failure, cardiovascular death, nonfatal heart attack, and hospitalization for heart failure in adults with CKD associated with type 2 diabetes. Similar approvals have been issued in Europe and other regions.

Those decisions were supported by the large phase 3 trials FIDELIO-DKD and FIGARO-DKD, which enrolled more than 13,000 patients with type 2 diabetes and CKD and tracked hard outcomes over years.

By contrast, FINE-ONE lasted six months, enrolled 242 participants, and used UACR rather than kidney failure or mortality as its primary outcome. While albuminuria reductions have been linked to better long-term outcomes in type 2 diabetes, that relationship is not definitively established in type 1 diabetes.

Caution from kidney specialists

In an accompanying editorial, Mayo Clinic nephrologists Aleksandra Kukla and Marie C. Hogan described FINE-ONE as “an important step” toward expanding treatment options for people with type 1 diabetes and kidney disease, but emphasized limits in what the results can prove.

They noted that the trial was relatively short and focused on patients with high albuminuria. Some people with type 1 diabetes experience progressive kidney decline even with low or normal UACR, and they were not represented.

The editorial also highlighted that the study excluded patients using SGLT2 inhibitors and GLP-1 receptor agonists—agents some clinicians prescribe off-label in type 1 diabetes despite concerns such as diabetic ketoacidosis risk—leaving unanswered questions about how finerenone might fit into future combination regimens.

Regulatory and access questions ahead

As of mid-March, finerenone’s approved indication remains limited to adults with CKD associated with type 2 diabetes. Bayer has said it plans to submit FINE-ONE data to regulators in the United States, Europe, and other regions to seek an expansion to type 1 diabetes.

Regulators will need to weigh whether improvements in a surrogate marker over six months are sufficient for a new indication, and how confidently evidence from type 2 diabetes can be extended to type 1 diabetes, which has different underlying biology and a thinner outcomes evidence base.

If approval expands, payers would still face decisions on cost and coverage. For now, any prescribing of finerenone for type 1 diabetes would be off-label and may not be reimbursed.

Clinicians say the findings should be viewed as an encouraging signal rather than an immediate new standard of care. Patients with type 1 diabetes and CKD are advised to continue prioritizing glucose and blood pressure control and established kidney-protective therapy such as ACE inhibitors or ARBs, while discussing emerging options and research opportunities with their care teams.

Whether finerenone becomes the first kidney-specific drug approved for type 1 diabetes will ultimately depend on evidence that it can do more than lower a lab value—that it can meaningfully change the long-term course of a disease that has gone too long without new answers.