In the world of clinical trials, the most dramatic thing that can happen is a study being stopped early. Not because of safety concerns—but because the drug is working so well that it would be unethical to keep giving some patients a placebo. That’s exactly what happened with the FLOW trial.
Published in the New England Journal of Medicine in July 2024, FLOW was the first-ever dedicated kidney outcomes trial for a GLP-1 receptor agonist. The results were so compelling that the independent data monitoring committee recommended stopping the trial ahead of schedule.
Why Kidney Disease Matters
Chronic kidney disease (CKD) affects approximately 37 million Americans—about 15% of the adult population. Diabetes is the leading cause, and roughly one in three adults with diabetes will develop some degree of kidney disease. CKD is progressive, often silent in early stages, and can lead to kidney failure requiring dialysis or transplant.
Until recently, the treatment options for slowing kidney disease progression in diabetic patients were limited to blood pressure medications (ACE inhibitors or ARBs), SGLT2 inhibitors (like empagliflozin or dapagliflozin), and the mineralocorticoid antagonist finerenone. The FLOW trial added semaglutide as a fourth pillar of kidney protection.
How the Trial Was Designed
FLOW enrolled 3,533 patients with type 2 diabetes and chronic kidney disease across 28 countries, with a median follow-up of 3.4 years. Participants had significant kidney impairment at baseline—average eGFR of 47 mL/min/1.73m² (indicating moderate-to-severe kidney disease) and elevated urine albumin levels indicating kidney damage.
The study compared once-weekly subcutaneous semaglutide at 1.0mg to placebo, with both groups continuing standard kidney-protective therapies. The primary endpoint was a composite of major kidney disease events: kidney failure (need for dialysis or transplant, or eGFR falling below 15), a 50% or greater decline in kidney function from baseline, or death from kidney-related or cardiovascular causes.
The Results
| Outcome | Semaglutide | Placebo | Risk Reduction |
|---|---|---|---|
| Primary kidney endpoint | 18.7% | 23.2% | 24% |
| All-cause death | 12.8% | 15.8% | 20% |
| Cardiovascular death | 7.0% | 9.6% | 29% |
| Major cardiovascular events | — | — | 18% |
| eGFR decline (slowed by) | — | 1.16 mL/min/yr | |
Perhaps the most striking number: the number needed to treat (NNT) to prevent one death was just 39 patients over 156 weeks. In kidney medicine, that’s an exceptionally efficient intervention.
What “Stopped Early” Means
When a clinical trial’s data monitoring committee stops a study early for efficacy, it means the benefit is so clear that continuing to give some patients a placebo would be ethically unjustifiable. This has only happened a handful of times in kidney disease research. It’s a strong signal of real-world impact.
How Semaglutide Protects Kidneys
The kidney-protective effects of semaglutide appear to work through multiple pathways:
- Reduced inflammation: Chronic inflammation drives kidney damage in diabetes. Semaglutide reduced inflammatory markers significantly.
- Blood pressure lowering: Systolic blood pressure dropped by an additional 2.23 mmHg compared to placebo, reducing strain on the kidneys.
- Albuminuria reduction: Urinary albumin-to-creatinine ratio (a key marker of kidney damage) decreased by 38% with semaglutide.
- Weight loss: Participants lost an average of 5.55 kg more than placebo, reducing metabolic stress on the kidneys.
- Blood sugar improvement: HbA1c dropped by an additional 0.81 percentage points, though benefits extended beyond glucose control.
GLP-1 receptors are expressed directly in the kidney, particularly in the proximal tubule, where they promote natriuresis (sodium excretion) and diuresis. This direct kidney action may contribute to protection beyond the drug’s metabolic effects.
Benefits Were Consistent Across All CKD Severities
A subgroup analysis presented at Kidney Week 2024 by Dr. Katherine Tuttle showed that semaglutide’s kidney benefits held up regardless of how severe a patient’s kidney disease was at baseline. Whether eGFR was below 30, between 30 and 45, between 45 and 60, or above 60 mL/min/1.73m², the hazard ratios for the primary kidney endpoint were consistently in semaglutide’s favor.
Benefits were also consistent regardless of baseline urine albumin levels and KDIGO risk classification. This suggests that semaglutide could benefit a broad range of CKD patients—from early-stage disease to more advanced cases.
The “Fourth Pillar” of Kidney Protection
Nephrologists now describe four evidence-based pillars for managing diabetic kidney disease:
- RAS blockade (ACE inhibitors or ARBs)—the foundation for decades
- SGLT2 inhibitors (empagliflozin, dapagliflozin)—proven in DAPA-CKD and EMPA-KIDNEY
- Finerenone—a non-steroidal mineralocorticoid receptor antagonist
- GLP-1 receptor agonists—now validated by FLOW
Only about 15% of FLOW participants were on SGLT2 inhibitors at baseline, and early subgroup analyses suggest the benefits of semaglutide may be additive—meaning patients on existing kidney-protective regimens could still benefit from adding a GLP-1.
What This Means for You
If you have type 2 diabetes and any degree of kidney disease, the FLOW trial provides compelling evidence that GLP-1 therapy may slow kidney decline, reduce cardiovascular events, and lower your risk of death. This is on top of any benefits from weight loss or blood sugar improvement.
For the estimated 37 million Americans with CKD—and especially the millions whose kidney disease is driven by diabetes—the FLOW trial represents a genuine breakthrough in available treatment options.
Talk to your healthcare provider about whether semaglutide might be appropriate as part of your kidney protection strategy.
Sources
- Perkovic V, et al. “Effects of Semaglutide on Chronic Kidney Disease in Patients with Type 2 Diabetes.” N Engl J Med. 2024;391:109-121. DOI: 10.1056/NEJMoa2403347
- American Diabetes Association. “Semaglutide Reduced Risk for Major Kidney Disease Events by 24%.” ADA 84th Scientific Sessions. June 2024.
- Mahaffey KW, et al. “Cardiovascular Outcomes With Semaglutide by Severity of CKD.” Eur Heart J. 2024.
- American College of Cardiology. FLOW Trial Summary. acc.org.