Hoping to improve sales of its Viagra drug, Pfizer Inc. has hired former presidential contender Bob Dole for a television advertising campaign to raise awareness about impotence. Dole, a former Senate majority leader, will participate in a series of public service activities, including speaking engagements and educational advertising that focus on impotence and men's health in general, the company said. New York-based Pfizer would not disclose how much it is paying Dole, who will not mention Viagra by name in the messages that will start early next year. The Dole ads mark Pfizer's first use of television advertising associated with Viagra. The company is weighing whether to use any ads that directly mention the product. In May, Dole, 75, acknowledged he participated in the trials for Viagra, which he has called "a great drug." Viagra was the most successful introduction of a new prescription drug in history, but its sales have not kept up the early pace. The drug is expected to have sales of $800 million for the year, far below the $1-billion estimates analysts initially predicted. Pfizer shares gained 88 cents to close at $114.88 on the New York Stock Exchange.