THE MEDIA BUSINESS: ADVERTISING; With its Viagra under attack by new rivals, Pfizer chooses a new agency for ads in the United States.

THE three-way war in the $2 billion-a-year category of prescription drugs that treat erectile dysfunction has claimed an initial casualty. The market leader, Viagra, pressed to defend its hegemony against two upstart competitors, is changing its general creative agency for campaigns aimed at American consumers.

Pfizer, the maker of Viagra, said yesterday that it would shift the creative duties for its general advertising, including television commercials and print ads, to McCann Erickson Worldwide in New York from Cline Davis & Mann in New York. Spending for the assignment was estimated at $100 million. The change, which came after a four-month review, was reported Monday night on Adage.com.

The shift expands McCann’s relationship with Pfizer; the agency already creates campaigns for Viagra in 30 countries in Asia, Europe and South America. McCann has also handled Bextra, a Pfizer drug for arthritis, for almost a year.

The work on Viagra for the United States will be led by McCann HumanCare, a recently formed health care marketing division of McCann, part of the McCann Worldgroup of the Interpublic Group of Companies.

Cline Davis, part of the Omnicom Group, keeps its assignments for Viagra campaigns aimed at health-care professionals, as well as for interactive advertising. Viagra has had no other agency for its domestic consumer ads since Pfizer established the erectile-dysfunction category in 1998, although the company recently replaced the work from Cline Davis with commercials created for the Canadian market by an agency in Toronto called Taxi.

The shift of the Viagra general consumer tasks reflects the blurring of ads for prescription drugs aimed at consumers — once forbidden — and those for products in traditional categories, like cereal and automobiles.

One hallmark of traditional marketing is competition among brand sellers, and that has certainly been the case with erectile-dysfunction drugs as Viagra, alone in the category for five years, confronts two new rivals.

”In a competitive market place, where you are no longer the only player, the power of your brand becomes even more important,” said Andrew F. Schirmer, managing director at McCann HumanCare.

”As an organization, we’re very comfortable building brands in some hotly contested market places,” he added, citing the ”Priceless” campaign by the McCann New York office for MasterCard International.

Although Mr. Schirmer declined to discuss details of the approach the agency might take for Viagra in the United States, he did cite the fact that there were many men who go without treatment and that with Viagra ”as the market leader, it’s our responsibility to get our fair share of those.”

”It means there’s work to be done,” he said. The drug makers estimate that only 13 percent of men with trouble getting and keeping erections are being treated.

One Viagra rival, Levitra, was introduced in August by the Bayer Pharmaceuticals division of the Bayer Corporation and GlaxoSmithKline. The other, Cialis, was introduced in November by Lilly Icos, a joint venture of Eli Lilly & Company and the Icos Corporation. By the spring, Levitra and Cialis had taken a combined share of about 15 percent of the market from Viagra, and more recently their combined market share has reached an estimated 25 percent, with about 14 percent for Cialis and about 11 percent for Levitra.

Focusing on only new prescriptions, Viagra’s market share has declined further, to an estimated 66 percent, with Cialis at around 19 percent and Levitra at 15 percent.

Cialis has used a single, consistent campaign since its debut, featuring couples in side-by-side bath tubs as a branding device. The ads are created by Grey Worldwide in New York, part of the Grey Global Group.

”We are so focused on one path, and we think it’s the right path,” said Matt Beebe, the brand team leader responsible for Cialis in the United States for Lilly Icos in Indianapolis.

”Cialis is a very different product, with 36 hours of efficacy, and as a result we have very different advertising,” he added. His reference was to the average duration of the effects of Cialis, compared with the average four-hour duration of Viagra and Levitra.

”While we’ll continue to make small adjustments in our ads like different visuals coming up,” Mr. Beebe said, ”our core message is going to be exactly the same.”

By contrast, Levitra, like Viagra, has been making more substantive changes in its ads. Levitra was introduced with a campaign infused with masculine imagery like a game of tossing a football through a tire swing and pep talks from the former coach Mike Ditka.

The brand switched gears in April, softening the tone by adding women to the pitches and spicing up the mood with sly suggestions about improved sexual performance. The Levitra agency is the Quantum Group in Parsippany, N.J., part of the WPP Group.

A spokeswoman at Ogilvy Public Relations, representing the Levitra marketers, Bayer and GlaxoSmithKline, said yesterday that they were at an offsite meeting and she had left a message for them seeking comment.

A spokesman for Pfizer in New York, Paul Ewing, said McCann was selected in the review because the agency ”brought unique insights to the table,” centered on ”the obstacles that prevent men with erectile dysfunction from seeing their doctors and if appropriate trying Viagra” as well as ”what motivates them to take action.”

While Pfizer ”really values our partnership with Cline Davis & Mann,” Mr. Ewing said, since the Viagra introduction ”our ongoing mission has been to continue to ensure we’re using the best insights available to break through the barriers and motivate consumer action.”

”We have been continually refreshing our message” since 1998, he added, and the review ”was part of that.”

Among the campaigns McCann will create, Mr. Ewing said, will be ads to continue a promotion introduced in April called the Viagra Value Card, which offers customers a free prescription for each six they buy. While such loyalty programs are unusual for prescriptions drugs, they are common in traditional product categories, representing another signal of the convergence in marketing techniques.

In addition to Cline Davis continuing with the health-care and interactive assignments, Mr. Ewing said, Pfizer will continue using Digitas as the direct marketing and relationship marketing agency for Viagra, an assignment awarded to the Digitas New York office in April.

The creative review for Viagra had been narrowed to McCann and another agency on the Pfizer roster, Merkley & Partners Healthworks in New York, part of the Merkley & Partners division of Omnicom.

Adage.com reported that the competition between the two finalists was so intense as to be tied at one point in the review.

”I’m not surprised by the strength of the competition,” Mr. Schirmer said, ”because it’s an agency where I used to be.” Indeed, he joined McCann HumanCare almost a year ago from Merkley, where he had been president and executive creative director.

When the creative review began, McCann and Merkley Healthworks were also competing against Cline Davis and another Pfizer roster agency, Berlin Cameron/Red Cell, part of the Red Cell division of WPP. Berlin Cameron was eliminated in late April and Cline Davis sometime after that.

A version of this article appears in print on , Section C , Page 6 of the National edition with the headline: THE MEDIA BUSINESS: ADVERTISING; With its Viagra under attack by new rivals, Pfizer chooses a new agency for ads in the United States. . Order Reprints | Today’s Paper | Subscribe