CLINICAL TRIAL SPOTLIGHT
Niacin and Steroid Combination in Trial for Retinal Vein Occlusion
Could a B vitamin be the key to finding a long-term solution to RVO?
ANDREW E. MATHIS, PhD, MEDICAL EDITOR
Despite retinal vein occlusions (RVOs) being a common cause of vision loss, no standard of care exists for treating them. Fewer than 10 studies are currently recruiting patients to study the treatment of RVO. One trial is studying the effectiveness and safety of niacin (vitamin B3) in combination topical steroid eyedrops. Retinal Physician spoke with Michael W. Gaynon, MD, of the Palo Alto Medical Foundation about this study.
"This has been an effort to define a relatively safe, effective, and inexpensive intervention for RVOs that might be easily and broadly applied without requiring the expertise of a retinal specialist," Dr. Gaynon said. "It may be especially useful in remote settings where subspecialty care is limited or where the cost may be a limiting factor. It avoids intravitreal injections and the associated risks."
Dr. Gaynon described how niacin works in RVO cases. "It's a vasodilator that works by generating prostaglandins, which in turn aid the production of nitric oxide synthase and then nitric oxide," he said. "We noticed its efficacy observing a patient with a new central RVO (CRVO) who improved over a few months from counting fingers vision to 20/50 after being given niacin for hyperlipidemia. This was better than the natural history of RVO would predict."
These observations were made before the use of intravitreal steroids, and no effective treatment for RVO was yet known. "We weren't sure if this was a coincidental finding or if niacin was somehow acting as a vasodilator to encourage more rapid collateral vessel formation and/or to alter retinal or choroidal blood flow in such a way as to reduce hypoxia and thereby downregulate VEGF," Dr. Gaynon said. A second patient had a similar experience. "We gradually felt our way forward, exploring the potential of this intervention in individuals who were not improving with observation, and along the way we found there was reversibility of effect if the niacin was discontinued." Plus, Dr. Gaynon has found that dosing RVO patients with niacin has had the benefit of improving lipid profiles, as niacin is a good drug for reducing LDL and raising HDL levels.
Another of the interesting things that Dr. Gaynon has found thus far is that this combination therapy seems more durable than others. Of course, there are significant variables. "The treatment seems to work best in nonischemic vein occlusions," Dr. Gaynon said. "It works less well in those patients with pre-existing diabetic retinopathy."
Dr. Gaynon explained the role of steroids, using an example of a highly myopic patient with macular edema whose vision had fallen from 20/25 to 20/200. "After a year and a half, she was still 20/200 in the CRVO eye," Dr. Gaynon said. "By this time, intravitreal steroids were being tried, but she wasn't willing to consider intravitreal or subtenons injections. She was willing to use a steroid eyedrop, which I doubted would work. We began topical steroids without much hope for improvement, but I was surprised to find she improved to 20/60 within 2 months and a month or 2 later reached 20/50." A few years later, she is now 20/30 on niacin alone, he says.
"I suspect the drops were being absorbed systemically and reached the posterior segment by that route, as opposed to direct penetration from the anterior segment," Dr. Gaynon continued. "More patients appeared to improve with this innocuous additional intervention, so we continued forward, in combination with the niacin. Here again, we observed reversibility of effect with discontinuation of the topical steroids."
Regarding other uses for niacin, Dr. Gaynon said, "It may turn out that this approach can be combined with anti-VEGF agents to decrease the number of injections required and speed the development of collaterals, which anti-VEGF agents and intravitreal steroids are unlikely to do. We have not used that approach in this study, since it would confuse interpretation of outcomes." RP