Pfizer, the world's largest pharmaceuticals group, is in discussions with the US Food and Drug Administration (FDA) about updating the safety warnings for its impotence drug Viagra after rare reports of loss of vision among users.
News of the potential problem with the drug, one of the world's best-known medical brands, helped push Pfizer's share price down by nearly 2 per cent yesterday. One of the compounds in Viagra is manufactured at Pfizer's Cork plant.
The FDA confirmed that it was investigating 38 reports of partial blindness caused by non-arteritic anterior ischemic optic neuropathy (NAION) in Viagra users, but said it had not determined whether the drug was to blame.
The FDA probe comes at a time of heightened sensitivity to drug safety in the wake of a series of health scares including the withdrawal of cox-2 inhibitor anti-inflammatory drugs after concerns about strokes and skin conditions.
Pfizer released a statement saying it was talking to the FDA about updating the Viagra label to reflect these incidents. But it stressed: "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 it had identified 23 cases of NAION-linked blindness or partial blindness. It was aware of one lawsuit, and the link between the ailment and Viagra had been highlighted in the Journal of Neuro-Opthamology in March. It has since been discussing updating information to doctors and users.
It said NAION and erectile dysfunction were common in men over 50 with high blood pressure, high cholesterol and diabetes, making it impossible to determine how far Viagra could be a contributory factor to the condition.
