People taking rosiglitazone (Avandia) to treat type 2 diabetes may be getting more from their prescription than anticipated. According to a study published in the June 2008 issue of the journal Archives of Ophthalmology, the drug may delay a disease that poses a major threat to the eyes of people with diabetes.

The disease—proliferative diabetic retinopathy—is caused when high blood glucose (hyperglycemia) damages the blood vessels in the back of the eye, prompting new, abnormal blood vessels to grow. While there are various stages of diabetic retinopathy, the advanced proliferative stage can lead to vision loss.

But new research, led by Lucy Q. Shen, MD, a fellow with the Jules Stein Eye Institute at the University of California, Los Angeles, suggests that those on rosiglitazone may delay progression to the serious proliferative stage. She says this may be because the drug inhibits abnormal blood vessels from forming. “If the cells can’t grow,” she says, “you can’t get retinopathy.”

Shen and colleagues reviewed medical information from 124 patients taking rosiglitazone who had received eye and medical care at the Joslin Diabetes Center in Boston between May 2001 and May 2003. Within the study group, including a matched control of 158 patients, was a subset of people who had severe nonproliferative diabetic retinopathy (an earlier stage of the disease).

After one year, 29 percent of the control group with severe nonproliferative diabetic retinopathy had the disease progress to the proliferative stage compared to 7.7 percent in the rosiglitazone group. After three years, 47 percent in the control group advanced from nonproliferative to proliferative retinopathy, while only 19.2 percent of the rosiglitazone group saw their disease progress to the more serious phase. The researchers calculated that taking rosiglitazone led to a 59 percent relative risk reduction of advancing to the more serious form of eye disease.

Shen and her team also found that over an average follow-up period of 2.8 years, those with severe nonproliferative diabetic retinopathy taking rosiglitazone were less likely to experience a three or more line decrease in clarity on a visual chart.

Does this mean you should switch to rosiglitazone right away? Not necessarily. Additional studies need to be conducted, Shen says, to analyze the possible benefits and drug safety risks: “This medication is not without its side effects, especially cardiovascular problems. The safety needs to be considered.”