Shares of pharmaceutical giant Pfizer rose more than one percent in opening trade Tuesday after the company announced it would sell its men\'s sexual aid Viagra over the Internet to beat counterfeits. After an initial increase to $29.18, in late morning trade the shares had pulled back to $28.92, for an 0.7 percent gain. On Monday Pfizer announced it was beginning to sell online Viagra, its prescription drug for erectile dysfunction (ED), to beat back the market for fake versions of the popular blue pill. Pfizer, which has earned billions of dollars on Viagra since introducing it 15 years ago, said the medication is its most counterfeited product. \"There are almost 24 million searches a year for Viagra online,\" Pfizer marketing executive Victor Clavelli said in a statement. \"By offering men with ED convenient access and a legitimate alternative to purchase Viagra online, our hope is that Pfizer will help rein in the distribution of fake ED products,\" he said. Pfizer will distribute Viagra over the Internet directly to customers with valid prescriptions in cooperation with the online service of CVS, one of the largest pharmacy chains in the United States. Analysts said Pfizer stood to benefit but that its approach could eventually threaten to cut out the pharmacies as middle-men in the drugs business. \"The makers of other drugs will be watching as well,\" said 24/7 Wall St. \"Viagra, which sells by prescription for $25 a tablet, is often faked by online sellers and sold as the real thing. That damages the drug\'s brand and keeps profits out of Pfizer\'s hands.\" \"Makers of weight-loss drugs will be watching Pfizer\'s Web sales closely, and these may be the next drugs to hit the market directly from manufacturers to patients.\"