The Merck diabetic macular edema trial known as BRUNELLO delivered a result with two sides. Presenting one-year data on 10 October 2026, Merck reported that its experimental eye drug remigromig met the main goal of matching an established injection, ranibizumab, on vision gains in people with diabetic macular edema. The same data showed more eye events linked to proliferative diabetic retinopathy, a sight-threatening complication, in patients given remigromig.
Here is what the numbers show, what the company says about them, and what remains unexplained.
Key takeaways from the Merck diabetic macular edema trial
- Both remigromig doses met the prespecified non-inferiority test against ranibizumab for visual acuity at week 52.
- Ranibizumab still produced larger average gains: 11.8 letters against 9.1 and 8.7 letters for the two remigromig doses.
- Events in a composite proliferative diabetic retinopathy (PDR) category occurred in 6.7% and 6.1% of remigromig patients, against 0.9% on ranibizumab.
- No secondary endpoint showed superiority over ranibizumab, and the non-inferiority margin was not disclosed in the material we reviewed.
- Merck plans to discuss the results with regulators. It has not announced a filing.
Merck diabetic macular edema trial: design and results
BRUNELLO (NCT06571045) is a Phase 2b/3 study that enrolled 984 adults with diabetic macular edema, a build-up of fluid in the central retina that blurs vision in people with diabetes. Participants were randomised one to one to one to remigromig 0.5 mg, remigromig 0.8 mg or ranibizumab 0.5 mg. All three groups received injections into the eye every four weeks in the first year. The second year uses a personalised treatment-interval approach. Full design details are in the ClinicalTrials.gov registry entry for BRUNELLO (NCT06571045).
The primary endpoint was the average change in best-corrected visual acuity, measured in letters on a standard eye chart, at week 52. According to the company, the results were:
- Remigromig 0.5 mg: +9.1 letters (95% confidence interval 8.1 to 10.1).
- Remigromig 0.8 mg: +8.7 letters (95% confidence interval 7.7 to 9.8).
- Ranibizumab 0.5 mg: +11.8 letters (95% confidence interval 10.7 to 12.8).
By our arithmetic, ranibizumab was ahead by 2.7 letters over the lower remigromig dose and 3.1 letters over the higher one. Both doses cleared the non-inferiority test, with adjusted p-values reported as 0.0129 and 0.0222. But non-inferiority means the new drug was not worse than the comparator by more than a set margin. It does not mean equivalent, and the margin itself was not given.
What the Merck diabetic macular edema trial found on safety
The disclosure that drew attention was in the eye-safety tables. Adverse events in a composite PDR-related category, which includes proliferative diabetic retinopathy, vitreous haemorrhage, iris and retinal neovascularisation and neovascular glaucoma, were reported in 6.7% of patients on remigromig 0.5 mg, 6.1% on 0.8 mg and 0.9% on ranibizumab. By our calculation that is roughly seven times the comparator rate. Discontinuations because of adverse events followed a similar pattern: 4.9%, 4.5% and 0.9%.
Merck describes both doses as generally well tolerated and says the PDR cases were generally manageable with standard care. It has also suggested the events could reflect the natural progression of diabetic eye disease. Those are the company’s interpretations. The category is a composite, so it is not a confirmed rate of PDR alone, and the material we reviewed gave no absolute event counts, severity, timing or baseline retinopathy by treatment group. Merck has said it is still analysing the signal.
Why the Merck diabetic macular edema trial matters
Most current treatments block a protein called VEGF. Remigromig works differently: it is a tri-specific antibody that activates the Wnt pathway, which is involved in maintaining the blood-retina barrier. A drug with a new mechanism could help patients who respond poorly to existing injections, and a personalised dosing schedule could in principle reduce visits. In our assessment, matching an established standard on vision is a real step for a first-in-class approach. But the mechanism cannot yet be linked to the safety imbalance, and the data do not show that it was caused by Wnt activation, only that it occurred more often.
Merck gained the drug through its 2024 acquisition of EyeBio, a deal worth $1.3 billion upfront with up to $1.7 billion more in milestones. A second pivotal diabetic macular edema study, BAROLO, is ongoing, and a Phase 2 study is testing the drug in neovascular age-related macular degeneration and retinal vein occlusion.
What we still do not know about the Merck diabetic macular edema trial
- The non-inferiority margin and the full statistical plan.
- Central retinal thickness results, which were not reported in the material we reviewed.
- Year-two outcomes under the personalised dosing schedule.
- Whether the PDR-related events happened in patients with more advanced retinopathy at baseline.
- What regulators will make of the safety balance. The general route to approval is described in the FDA drug development process.
What patients should know after the Merck diabetic macular edema trial
Remigromig is investigational and not approved anywhere. People with diabetes are advised to have regular dilated eye examinations, because early diabetic eye disease often causes no symptoms. The National Eye Institute has patient information on diabetic retinopathy. Treatment decisions belong with an eye specialist.
For other recent trials where the headline and the detail did not match, see our reports on the aprocitentan hypertension analysis, the pulmonary fibrosis Phase 3 trial, the tovinontrine heart failure study and the Bristol Myers radiopharmaceutical trial, or browse more pharmaceutical news.
Frequently asked questions
Did the Merck diabetic macular edema trial succeed?
On its primary endpoint, yes: both remigromig doses met non-inferiority to ranibizumab for visual acuity at week 52. It did not show superiority, and it raised safety questions.
What is remigromig in the Merck diabetic macular edema trial?
An investigational tri-specific antibody that activates the Wnt pathway, developed by Merck after its acquisition of EyeBio.
What safety concerns came out of the Merck diabetic macular edema trial?
A higher rate of PDR-related events, 6.7% and 6.1% against 0.9% on ranibizumab, plus more discontinuations because of adverse events.
Is remigromig from the Merck diabetic macular edema trial approved?
No. Merck says it will discuss the results with regulators.
How many patients were in the Merck diabetic macular edema trial?
984 adults with diabetic macular edema were randomised across three groups.
How we reported this: we relied on the company’s announcement of one-year data and on the trial registry entry. Results are the company’s and have not been peer reviewed. Figures labelled as ours are our own calculations. Last updated: 13 October 2026. This article is news reporting and not medical advice.