Pfizer to sue fake Viagra merchants

Pfizer, the world’s biggest drug-maker, is suing five Internet pharmacies and trying to seize the domain names of than two dozen others to stop the sale of counterfeit Viagra, the male impotence drug.

The company is starting an advertising campaign to warn consumers about fake Viagra.

Viagra’s worldwide revenue was $389m in the second quarter. About 20% of men who buy erectile dysfunction medicines do so over the Internet.