Retatrutide and Kidney Disease: CKD Research

Introduction

Chronic kidney disease (CKD) affects an estimated 850 million people worldwide and is closely linked to obesity, type 2 diabetes, and cardiovascular disease. GLP-1 receptor agonists have recently demonstrated kidney-protective effects in dedicated trials, most notably the semaglutide FLOW trial. Retatrutide, as a triple receptor agonist targeting GIP, GLP-1, and glucagon receptors, is now being evaluated for potential kidney benefits through both post-hoc analyses of its Phase 2 program and a dedicated Phase 2b kidney trial (TRANSCEND-CKD).

It is important to state clearly that evidence for retatrutide in kidney disease is emerging and preliminary. No Phase 3 kidney outcomes trial has been completed. The data discussed below come from post-hoc subgroup analyses and a small mechanistic trial, and should be interpreted with appropriate caution.

Phase 2 Post-Hoc Kidney Data

Urinary Albumin-to-Creatinine Ratio (UACR)

Post-hoc analyses of the Phase 2 retatrutide trials examined changes in urinary albumin-to-creatinine ratio (UACR), a key marker of kidney damage. Elevated UACR indicates that the kidneys are leaking protein into the urine, which is both a marker of existing kidney injury and a predictor of future kidney function decline.

In participants with type 2 diabetes, retatrutide 12 mg was associated with approximately 37% reduction in UACR. In the obesity population (without diabetes), the reduction was approximately 31.5% at the same dose.

These reductions are notable because UACR lowering has been established as a reliable surrogate for kidney protection. Therapies that reduce UACR, such as SGLT2 inhibitors and ACE inhibitors, have consistently demonstrated kidney outcomes benefit in subsequent outcomes trials.

Estimated Glomerular Filtration Rate (eGFR)

In the obesity population, retatrutide was associated with an increase in estimated glomerular filtration rate (eGFR) of approximately 8.5 mL/min/1.73m² at the 12 mg dose. An increase in eGFR suggests improved kidney filtration capacity, though the interpretation requires nuance.

Short-term eGFR increases can reflect improved hemodynamic conditions (better blood flow to the kidneys) rather than structural kidney improvement. The clinical significance of eGFR changes observed over the relatively short Phase 2 treatment period is uncertain. Longer-duration studies are needed to determine whether these changes are sustained and translate into kidney function preservation.

Limitations of Post-Hoc Analyses

These kidney findings come from post-hoc analyses, meaning they were not pre-specified endpoints of the original trials. Post-hoc analyses are hypothesis-generating rather than confirmatory. The trials were not designed or powered to detect kidney outcomes, the patient populations were not selected based on kidney disease status, and there is an inherent risk of finding favorable results by selectively analyzing subgroups after seeing the data. These results should be viewed as early signals warranting further investigation, not as established evidence.

TRANSCEND-CKD Trial

Trial Design

To prospectively evaluate retatrutide’s effects on kidney function, Eli Lilly initiated TRANSCEND-CKD, a Phase 2b mechanistic study. The trial design paper was published in Nephrology Dialysis Transplantation (NDT) in 2025, providing detailed rationale and methodology.

Key design features:

Significance of Trial Design

The eGFR eligibility range of 25-75 mL/min/1.73m² encompasses moderate to severe CKD (stages 3a, 3b, and 4). This range is clinically important because it includes patients at substantial risk of progression to kidney failure but who still have sufficient kidney function to potentially benefit from early intervention.

By including patients with and without type 2 diabetes, the trial can help determine whether retatrutide’s kidney effects are mediated purely through metabolic improvements (glycemic control, weight loss, blood pressure reduction) or whether there are direct kidney-protective mechanisms independent of diabetes status.

Mechanistic Endpoints

As a mechanistic study, TRANSCEND-CKD is designed to explore how retatrutide affects kidney physiology rather than to prove that it prevents hard kidney outcomes (such as progression to dialysis). Expected endpoints include changes in eGFR, UACR, kidney biomarkers, and potentially measured GFR using gold-standard techniques. This approach provides deeper insight into the drug’s kidney effects than a standard efficacy trial, though it cannot substitute for a large outcomes trial.

Potential Mechanisms of Kidney Benefit

Retatrutide’s triple receptor mechanism offers several pathways through which it could affect kidney function.

GLP-1 Receptor-Mediated Effects

GLP-1 receptors are expressed in the kidney, and GLP-1 receptor agonism has been associated with several renal effects:

• Natriuresis: GLP-1 receptor activation promotes sodium excretion, which may reduce intraglomerular pressure and protect the kidney from hyperfiltration injury
• Anti-inflammatory effects: GLP-1 receptor agonism reduces kidney inflammation and oxidative stress in preclinical models
• Hemodynamic effects: GLP-1 receptor activation may improve renal blood flow and reduce glomerular hypertension

GIP Receptor-Mediated Effects

The role of GIP receptor agonism in kidney physiology is less well characterized than GLP-1. GIP receptors are expressed in renal tissue, and emerging data suggest that GIP signaling may influence tubular sodium handling and electrolyte balance. The contribution of GIP receptor agonism to retatrutide’s kidney effects, if any, remains to be elucidated.

Indirect Effects Through Metabolic Improvement

Many of retatrutide’s metabolic effects independently benefit kidney function:

• Weight loss: Obesity is an independent risk factor for CKD development and progression. The 26-29% weight loss achieved with retatrutide reduces kidney hyperfiltration, intraglomerular pressure, and adipose-derived inflammation
• Blood pressure reduction: Hypertension is the second leading cause of CKD. The 14 mmHg SBP reduction observed with retatrutide 12 mg (TRIUMPH-4 data) would be expected to slow kidney function decline
• Glycemic control: In patients with type 2 diabetes, the potent HbA1c reductions achieved with retatrutide reduce glucotoxicity-mediated kidney damage
• Lipid improvement: Dyslipidemia contributes to kidney inflammation and fibrosis; the substantial lipid improvements observed with retatrutide may provide additional renal benefit

Cross-Trial Context

Semaglutide FLOW Trial

The semaglutide FLOW trial (2024) was the first dedicated kidney outcomes trial for a GLP-1 receptor agonist. It demonstrated that semaglutide 1.0 mg reduced the risk of clinically important kidney outcomes by 24% in patients with type 2 diabetes and CKD. The trial was stopped early for efficacy, establishing that GLP-1 receptor agonism provides meaningful kidney protection in diabetic kidney disease.

The FLOW trial result is relevant to retatrutide because it establishes proof of concept that the GLP-1 component of retatrutide’s mechanism has kidney-protective potential. However, whether retatrutide’s additional GIP and glucagon receptor agonism enhances, diminishes, or does not affect this benefit is unknown.

Tirzepatide Kidney Data

Tirzepatide (dual GIP/GLP-1 agonist) has shown kidney-related biomarker improvements in its clinical program, including UACR reductions in the SURPASS trials for type 2 diabetes. Dedicated kidney outcome analyses for tirzepatide are ongoing. These data will help clarify whether adding GIP receptor agonism to GLP-1 agonism provides incremental kidney benefit.

TRIUMPH-Outcomes

The TRIUMPH-Outcomes trial (NCT06383390) includes kidney outcomes as part of its combined cardiovascular and kidney endpoint. This event-driven trial in patients with obesity and established ASCVD or CKD will ultimately provide the most definitive evidence regarding retatrutide’s kidney effects, but results are not expected until approximately 2029 or later.

Current Evidence Level

The kidney evidence for retatrutide should be classified as emerging:

• Available: Post-hoc Phase 2 analyses showing UACR reduction (37% in T2D, 31.5% in obesity) and eGFR improvement (8.5 mL/min/1.73m² in obesity)
• Underway: TRANSCEND-CKD (Phase 2b, 146 participants, mechanistic endpoints)
• Planned/Recruiting: TRIUMPH-Outcomes (Phase 3, event-driven, cardiovascular + kidney outcomes)
• Not yet available: No Phase 3 kidney outcomes data; no evidence that retatrutide prevents CKD progression, kidney failure, or dialysis

Patients with CKD should not use retatrutide based on current evidence. The drug is investigational and not approved for any indication. Established therapies for CKD, including SGLT2 inhibitors, ACE inhibitors/ARBs, and finerenone, have robust outcomes evidence and should form the foundation of CKD management.

Summary

Retatrutide has shown encouraging early signals for kidney benefit, including UACR reductions and eGFR improvements in Phase 2 post-hoc analyses. The TRANSCEND-CKD Phase 2b trial (146 participants, eGFR 25-75) is designed to provide mechanistic understanding of these effects. The drug’s multiple mechanisms of action, including GLP-1-mediated natriuresis and anti-inflammatory effects, substantial weight loss, blood pressure reduction, and glycemic control, provide biological plausibility for kidney protection.

However, all kidney evidence is currently preliminary. No Phase 3 kidney outcomes data exist. The TRIUMPH-Outcomes trial will eventually provide definitive evidence, but results are years away. Until then, retatrutide’s kidney effects remain a promising research direction, not an established clinical benefit.

Frequently Asked Questions

Is retatrutide being studied for kidney disease?

Yes. Eli Lilly is conducting TRANSCEND-CKD, a Phase 2b mechanistic trial in 146 participants with overweight/obesity and CKD (eGFR 25-75 mL/min/1.73m²). The trial design paper was published in Nephrology Dialysis Transplantation in 2025. Additionally, the TRIUMPH-Outcomes trial includes kidney endpoints.

Has retatrutide shown any kidney benefits in clinical trials?

Post-hoc analyses of Phase 2 data showed UACR reductions of approximately 37% in participants with type 2 diabetes and 31.5% in participants with obesity, along with eGFR increases of approximately 8.5 mL/min/1.73m² in the obesity population at the 12 mg dose. These are preliminary findings from analyses that were not pre-specified.

Can retatrutide replace current CKD treatments?

No. Retatrutide is investigational and not approved for any indication. Established CKD therapies with proven outcomes data, including SGLT2 inhibitors, ACE inhibitors/ARBs, and finerenone, remain the standard of care. Any eventual role for retatrutide in CKD management would depend on Phase 3 outcomes data that do not yet exist.

How does retatrutide compare to semaglutide for kidney disease?

Semaglutide has proven kidney outcomes data from the FLOW trial, which demonstrated a 24% reduction in clinically important kidney outcomes in patients with type 2 diabetes and CKD. Retatrutide has only preliminary surrogate marker data from post-hoc analyses and a small mechanistic trial. No direct comparison is possible at this stage of development.

When will kidney outcomes data for retatrutide be available?

The TRANSCEND-CKD trial (Phase 2b, mechanistic) should report relatively soon given its 24-week duration, though no public timeline has been provided. The definitive kidney outcomes data will come from the TRIUMPH-Outcomes trial, which is event-driven and not expected to report until approximately 2029 or later.

Does retatrutide affect kidney function in people without kidney disease?

In the Phase 2 obesity trial (participants without known CKD), retatrutide was associated with eGFR increases and UACR reductions, suggesting that even in populations without established kidney disease, there may be favorable effects on kidney biomarkers. However, these findings are preliminary, and the clinical significance for people with normal kidney function is uncertain.