October 3, 2014 — Pfizer’s blockbuster erectile dysfunction drug Viagra is already known to cause vision problems, but a new study suggests that people with a common gene mutation might be at risk of permanent vision loss.
The active ingredient in Viagra, sildenafil, treats erectile dysfunction by inhibiting the enzyme PDE5, but it can also inhibit PDE6. The problem is that PDE6 is important for transmitting light signals from the retina to the brain.
In clinical trials, men on high doses of Viagra had side effects like blurry vision, sensitivity to bright light, and altered color vision.
About 1 in 50 people have a genetic mutation that produces less PDE6 than normal. When people have two copies of this genetic mutation, they can develop Retinis Pigmentosa, the most common genetic cause of blindness.
It is possible that people who have normal vision but carry one copy of the mutation could be more susceptible to visual side effects if they take Viagra.
Researchers decided to investigate the side effect in mice. They found that mice on Viagra had temporary vision problems. Mice who were carriers of the mutation had more serious vision problems, including early signs of cell death, suggesting a possible risk of permanent visual degeneration.
The study was published in Experimental Eye Research by researchers from the University of New South Wales in Australia.
Dr. Nivison-Smith, the lead author on the study, warned:
“We are concerned that people who have normal vision but who carry a single copy of the mutant gene for the blinding disease, Retinitis Pigmentosa, could be more susceptible to these changes. … These finding are highly significant because about one in 50 people are likely to be carriers of recessive genes which cause retinal disease but are unlikely to know this, because their vision is normal.”
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