Washington, May 28: US regulators has said they have received more than 40 reports of a type of blindness in men taking impotence drugs, most involving Pfizer Inc.'s Viagra, but have not determined if the medicines were responsible.
The food and drug administration said yesterday it has about 38 reports of the rare condition among Viagra users, four reports among users of Eli Lilly and Co.'s Cialis and one report in a man who took Glaxosmithkline PLC's Levitra.
More than 23 million men worldwide have taken Viagra over the past seven years, Pfizer said. Reports are extremely rare of the condition known as non-arteritic anterior ischemic optic neuropathy (NAION), the company said. Naion can cause permanent vision loss in one or both eyes.
''FDA is aware of these reports but has not determined there is a cause and effect due to use of Viagra ... We're working with the company to make sure this information is available to doctors and patients,'' FDA spokeswoman Susan Cruzan told news agencies.
New York-based Pfizer said it is weighing a change to the Viagra label. But it emphasized no proof exists that links the blindness to the drug, which was introduced in 1998 and had 1.68 billion dollars in sales in 2004.
''While we expect the FDA to take these cases seriously, we do not believe they warrant concern with the product at this time,'' AG Edwards sons analyst Al Rauch said in a research note.
The news pushed shares of Pfizer, a component of the Dow Jones industrial average, down more than 2 percent, weighing on the broader market.
Viagra's label currently lists the most common side effects as headache, facial flushing and upset stomach, and says less common events are bluish or blurred visions and sensitivity to light that may occur for a short time.
''There is no evidence showing that Naion occurred more frequently in men taking Viagra than men of similar age and health who did not take Viagra,'' Pfizer said in a statement.
Dr. Michael Berelowitz, Pfizer's vice president for worldwide medical, said in an interview he did not think the FDA would require a ''black box'' warning - the strongest for prescription drugs - about the Naion reports.
Pfizer contacted the FDA about the blindness cases in March, after a study in the journal of neuro-ophthalmology reported seven Naion cases in Viagra users, Berelowitz said. The study said the cases occurred within 36 hours after the men took Viagra.
Bureau Report