After over 40 incidents of sudden, irreversible vision loss among users of the drug Viagra and other similar drugs which treat impotency, the U.S. Food and Drug Administration (FDA) is investigating whether the drugs can cause a rare kind of sudden blindness.
FDA officials are now in talks with Pfizer Inc., the maker of Viagra, about adding the new information to its product label.
But worrying though the incidents are, both the agency and Pfizer say it is unclear whether the drug was actually associated with the blindness as many Viagra users suffer from diabetes and high blood pressure, which are conditions that have been previously linked to a similiar sudden vision loss.
Sudden blindness is caused by the blockage of blood flow to the optic nerve and is most common in older people, the ones more likely to use Viagra. Upto an estimated 6,000 Americans suffer an optic blockage each year.
Pfizer estimates that about 23 million men worldwide have taken the drug and the company says that a review of 103 clinical trials with Viagra involving 13,000 patients found no reports of the sudden blindness, known as non-arteritic anterior ischemic optic neuropathy (NAION).
Suzanne Trevino a spokeswoman for the FDA, also says that it has not been determined that there is a cause and effect due to these drugs. She says the FDA is working with the company to ensure that this information is available to doctors and patients.