What FLOW Actually Changes in Clinical Practice

At a glance

Field	Detail
Trial name	FLOW (Evaluate Renal Function with Semaglutide Once Weekly)
N	3,533
Intervention	Subcutaneous semaglutide 1 mg weekly
Comparator	Matched placebo
Duration	Median 3.4 years (stopped early at prespecified interim analysis)
Primary endpoint	Composite of persistent ≥50% eGFR decline, persistent eGFR <15 mL/min/1.73 m², kidney replacement therapy initiation, or kidney death
Key result	HR 0.76 (95% CI 0.66 to 0.88; P = 0.0003) for the primary composite (PubMed 38785350)

The Trial Population Most Clinicians Overlook

Reading the abstract gives you the topline. Reading the supplementary appendix gives you prescribing guidance. FLOW enrolled adults with type 2 diabetes, an eGFR of 50 to 75 mL/min/1.73 m² with a urine albumin-to-creatinine ratio (UACR) of 300 to 5,000 mg/g, or an eGFR of 25 to 50 with a UACR of 100 to 5,000 mg/g (PubMed 38785350). That second stratum matters. It means FLOW deliberately tested semaglutide in patients with stage 3b and stage 4 CKD, a group that had been largely excluded from prior GLP-1 receptor agonist cardiovascular outcome trials.

Baseline characteristics reinforce the point. Mean eGFR was 47 mL/min/1.73 m². Median UACR was roughly 568 mg/g. Over 95% were already on renin-angiotensin system (RAS) blockade, and approximately 15.6% were on SGLT2 inhibitors at randomization. These patients were sick, treated, and still progressing. That is the exact population where clinicians need new options.

How the Kidney Composite Broke Down

The primary composite favored semaglutide across every component, but the magnitudes differed.

The hard endpoint of kidney replacement therapy showed no statistically significant separation. The trial's power for that single component was limited by both sample size and early termination. Clinicians should recognize that the 24% composite reduction was driven predominantly by sustained eGFR decline rather than by dialysis prevention directly measured in this trial (PubMed 38785350).

eGFR Slope: The Number That Changes Prescribing Conversations

Beyond the composite, FLOW reported the annual rate of eGFR change. In the semaglutide arm, the total slope was approximately -2.19 mL/min/1.73 m² per year versus -3.36 in placebo, yielding a between-group difference of 1.16 mL/min/1.73 m² per year. Over a decade, that difference compounds meaningfully. For a patient starting at eGFR 45, an extra 1.16 mL/min per year of preserved function could delay stage 5 CKD by several years, a framing patients understand immediately when discussing treatment.

There is a caveat. GLP-1 receptor agonists produce an initial hemodynamic eGFR dip similar to the pattern seen with SGLT2 inhibitors. FLOW's chronic slope (from week 8 onward) showed an even more favorable difference: 1.39 mL/min/1.73 m² per year. Clinicians familiar with the "dapagliflozin dip" from DAPA-CKD (PubMed 32970396) should counsel patients that the same early eGFR drop can occur with semaglutide and does not warrant discontinuation.

The HealthRX.com Practice-Change Framework

Not every positive RCT changes what happens in clinic. We score FLOW against five gates that separate "interesting data" from "Monday morning behavior change."

1. Regulatory label update. In March 2025, the FDA expanded the semaglutide (Ozempic) label to include reduction in the risk of sustained eGFR decline, end-stage kidney disease, and cardiovascular death in adults with type 2 diabetes and CKD (FDA Ozempic label). Label change is the strongest lever for formulary access.

2. Guideline incorporation. The 2024 KDIGO guideline update explicitly recognized GLP-1 receptor agonists as having kidney outcome data, moving them up the treatment algorithm for patients with T2D and CKD who have not reached glycemic targets or who need cardiovascular/kidney risk reduction beyond SGLT2 inhibitors (KDIGO 2024 guideline). The ADA Standards of Care 2025 similarly elevated GLP-1 RAs for kidney protection.

3. Formulary and access shift. Semaglutide is already on most commercial formularies for diabetes. The new kidney indication gives endocrinologists and nephrologists a second prior authorization pathway. In practice, supply constraints from obesity-indication demand have been the real barrier, not formulary status.

4. Additive benefit with existing standard of care. About 15.6% of FLOW participants were on an SGLT2 inhibitor at baseline. The trial was not designed or powered to test semaglutide as add-on to SGLT2 inhibition specifically, so the interaction is uncertain. Post-hoc subgroup analyses did not show a significant interaction by baseline SGLT2i use, but the subgroup was small. This is the single most important unanswered clinical question coming out of FLOW.

5. Population generalizability. FLOW excluded patients with type 1 diabetes, non-diabetic CKD, and eGFR <25 without heavy albuminuria. The results should not be extrapolated to those groups. For CKD patients without diabetes, the EMPA-KIDNEY trial with empagliflozin (PubMed 36331190) and the ongoing studies of GLP-1 RAs in non-diabetic kidney disease will need to fill that gap.

Where FLOW Sits Relative to SGLT2 Inhibitor Kidney Trials

Clinicians will inevitably compare FLOW to CREDENCE (canagliflozin), DAPA-CKD (dapagliflozin), and EMPA-KIDNEY (empagliflozin). Direct cross-trial comparisons are unreliable, but the magnitudes are informative for calibrating expectations.

The hazard ratios overlap. FLOW's slightly wider confidence interval and higher NNT partly reflect the early stop, which tends to overestimate treatment effects in some analyses and underestimate them in others depending on the alpha spending function. The point is that semaglutide adds a second mechanistic class with kidney protection. It does not replace SGLT2 inhibitors.

Practical Prescribing Scenarios After FLOW

Patient already on an SGLT2 inhibitor and still progressing. Adding semaglutide is now reasonable and label-supported, though evidence for the combination specifically is still weak. Start at 0.25 mg weekly, titrate to 1 mg over 8 weeks, monitor GI tolerability, and recheck eGFR/UACR at 3 months.

Patient intolerant of SGLT2 inhibitors. Semaglutide becomes the preferred second agent after maximized RAS blockade and finerenone (if indicated by the FIDELIO/FIGARO data). FLOW provides the kidney composite evidence that was previously missing for this clinical slot.

Patient with eGFR 25 to 30. FLOW included these patients (the lower eGFR stratum went to 25). The Ozempic label does not require dose adjustment for kidney function. GLP-1 RAs are not renally cleared, so the pharmacokinetic argument for use in low-eGFR patients is sound.

Patient with obesity-related CKD but no diabetes. FLOW does not cover this population. Prescribing off-label for kidney protection without diabetes is unsupported by these data.

Limitations the Authors Reported (and One They Didn't)

The FLOW investigators acknowledged several constraints. The trial was stopped early after a median follow-up of 3.4 years, limiting the ability to assess very long-term outcomes and hard endpoints like dialysis. GI adverse events (nausea, vomiting, diarrhea) were more common with semaglutide (approximately 45.5% vs. 33.0%), and a higher proportion of semaglutide-treated patients discontinued for adverse events.

The limitation the paper does not emphasize: FLOW was sponsored by Novo Nordisk and conducted almost entirely within the company's clinical operations infrastructure. This is standard for large outcome trials, but it means independent replication does not yet exist. The single-sponsor, single-molecule design is a structural feature of the evidence base, not a flaw per se, but it warrants acknowledgment when translating to practice.

What Should Change on Monday Morning

For nephrologists and endocrinologists managing type 2 diabetes with CKD stages 3 to 4: semaglutide now has a kidney-specific evidence base. It should be discussed alongside SGLT2 inhibitors and finerenone at the point of care. The remaining question is sequencing and combination, not whether semaglutide has kidney benefit. That question was answered by FLOW (PubMed 38785350).

Frequently asked questions

›How large was the kidney benefit of semaglutide in FLOW?

Semaglutide reduced the primary kidney composite endpoint by 24% (HR 0.76, 95% CI 0.66 to 0.88). The trial was stopped early for overwhelming efficacy after a median of 3.4 years of follow-up.

›Did FLOW show semaglutide prevents dialysis?

The kidney replacement therapy component alone did not reach statistical significance (HR 0.95). The composite benefit was driven by prevention of sustained eGFR decline. Longer follow-up would be needed to demonstrate dialysis prevention definitively.

›Can semaglutide be used with an SGLT2 inhibitor for kidney protection?

About 15.6% of FLOW participants were on an SGLT2 inhibitor at baseline. The trial was not powered to confirm additive benefit of the combination. Prescribing both is reasonable but based on indirect evidence and guideline recommendations rather than a dedicated combination trial.

›Does semaglutide need dose adjustment in CKD?

No. GLP-1 receptor agonists are not renally cleared. The Ozempic prescribing label does not require dose modification based on eGFR. FLOW enrolled patients with eGFR as low as 25 mL/min/1.73 m².

›Which guidelines changed after FLOW?

KDIGO's 2024 update and the ADA's 2025 Standards of Care both elevated GLP-1 receptor agonists in the treatment algorithm for type 2 diabetes with CKD. The FDA also expanded the Ozempic label to include kidney risk reduction.

›How does FLOW compare to DAPA-CKD or CREDENCE?

Direct comparisons across trials are unreliable. Hazard ratios for the primary composite were 0.76 for FLOW, 0.61 for DAPA-CKD, and 0.70 for CREDENCE. Differences in populations, endpoint definitions, and follow-up durations limit head-to-head interpretation.

›What about patients with CKD but no diabetes?

FLOW enrolled only patients with type 2 diabetes. There is no RCT evidence supporting semaglutide for kidney protection in non-diabetic CKD. Ongoing studies may address this gap.

›What were the main side effects in FLOW?

Gastrointestinal events (nausea, vomiting, diarrhea) occurred in roughly 45.5% of semaglutide patients versus 33.0% on placebo. Treatment discontinuation due to adverse events was higher with semaglutide. No new safety signals emerged beyond the known GLP-1 RA profile.

›Was the FLOW trial stopped early, and does that matter?

Yes, FLOW was terminated at a prespecified interim analysis for efficacy. Early stopping can inflate effect estimates in some statistical frameworks. The robustness of the benefit across sensitivity analyses reduces but does not eliminate this concern.

›Should nephrologists prescribe semaglutide now?

For patients with type 2 diabetes and CKD stages 3 to 4 who remain at risk despite RAS blockade (and potentially an SGLT2 inhibitor), semaglutide is now a guideline-supported option with a kidney-specific indication on the FDA label.

References

1. Perkovic V, Tuttle KR, Rossing P, et al. Effects of semaglutide on chronic kidney disease in patients with type 2 diabetes. N Engl J Med. 2024;391(2):109-121. PubMed
2. Heerspink HJL, Stefánsson BV, Correa-Rotter R, et al. Dapagliflozin in patients with chronic kidney disease. N Engl J Med. 2020;383(15):1436-1446. PubMed
3. The EMPA-KIDNEY Collaborative Group. Empagliflozin in patients with chronic kidney disease. N Engl J Med. 2023;388(2):117-127. PubMed
4. Ozempic (semaglutide) prescribing information. U.S. Food and Drug Administration. FDA Label
5. KDIGO 2024 Clinical Practice Guideline for Diabetes Management in Chronic Kidney Disease. Kidney Int. 2024. PubMed