Low and moderate dosing shows the most potential in preventing AMD for patients with diabetes.
Researchers continue to pursue new preventative measures for age-related macular degeneration (AMD).
However, new research suggests metformin could be a valuable therapy in preventing the disease, which is the leading cause of irreversible blindness in older adults worldwide.
A team, led by Andrea L. Blitzer, MD, Department of Ophthalmology and Visual Science, University of Chicago Medical Center, examined whether metformin use is linked to reduced odds of developing AMD.
In the case-control study, the investigators identified 312,404 patients from a nationwide health insurance claims database that include a population-based sample of patients. They used the data from individuals at least 55 years old with newly diagnosed AMD from January 2008 to December 2017.
They then matched this patient population with a control group with 312,376 participants.
The exposures in the study included dosage of metformin and exposure to other prescribed medications, as identified from outpatient drug claims.
The investigators sought main outcomes of the risk of developing AMD.
Overall, the case group had a slightly higher percentage of patients with diabetes (n = 81,262; 26.0%) than the control group (n = 79,497; 25.5%).
The use of metformin was linked to reduced odds of developing AMD (OR, 0.94; 95% CI, 0.92-0.96). However, this association was dose dependent with low-to-moderate doses of the drug showing the greater potential benefit (dosages over 2 years, 1-270 g; OR, 0.91 95% CI, 0.88-0.94; 271-600 g; OR, 0.90; 95% CI, 0.87-0.93; 601-1080 g; OR, 0.95; 95% CI, 0.92-0.98).
In addition, doses more than 1080 g over 2 years did not reduce the odds of developing AMD.
Both the reduction in odds ratio and the dose-dependent response were found in a cohort consisting only of the patients with diabetes.
Overall, metformin was linked to a decreased odds ratio of AMD in patients with diabetes without coexisting diabetic retinopathy (OR, 0.93; 95% CI, 0.91-0.95). However, there was a risk factor in patients with diabetic retinopathy (OR, 1.07; 95% CI, 1.01-1.15).
Metformin Shows Promise
The results suggest metformin could ultimately be used as a preventative therapy for AMD and could be studied further in future clinical trials.
“When looking only at patients with diabetes, we saw a preservation of the dose-dependent decrease in the odds of patients developing AMD,” the authors wrote. “Metformin does not appear to be protective in patients with diabetes and coexisting diabetic retinopathy.”
In 2019, researchers found patients who take metformin had a 58% reduced risk of developing AMD (OR, 0.58; 95% CI, 0.43-0.79).
Investigators from the University of Florida conducted a retrospective case-controlled study examining whether metformin use was associated with decreased risk of developing AMD. The investigators pulled medical records from University of Florida health clinic patients older than 55 years and matched every AMD case with 3 controls.
There were significantly decreased odds of developing AMD among metformin users, the investigators learned. This was true when they used both univariate analysis and conditional multivariable logistic regression.
Diabetes itself was associated with a statistically significant decreased risk for developing AMD, the investigators found. They believe that the effect of metformin use is independent of a diabetes diagnosis.
The study, “Association of Metformin Use With Age-Related Macular Degeneration,” was published online in JAMA Ophthalmology.