Facing generic competition for its “little blue pill,” Pfizer recently started selling a chewable form of Viagra in Mexico. It is called Viagra Jet, and Pfizer says it may also market it to other nations in the developing world, if not the United States.

Levitra, another erectile dysfunction drug, is now sold as a dissolvable tablet in nine European countries and may come to American pharmacies as soon as this month under the name Staxyn. That new form of the drug, which fizzes and dissolves in seconds, is marketed in a pocket-size, midnight-black box for men who prefer to take it discreetly, without water.

The third drug for erectile dysfunction to reach the market, Cialis, now eight years old, is racing ahead of the others because of two ideas that have proven extremely popular: an everyday pill and a 36-hour “weekender.” Cialis is projected to become the top-selling of the three drugs in the world this year, passing Viagra.

The market for drugs to correct erectile dysfunction has passed $5 billion a year from sales to tens of millions of men. And it is increasingly being driven by novel applications to compete with the lower-priced generics on the horizon.

“ ‘Gimmick’ is a strong word, but all of this is designed to create new brand identities,” Dr. Joseph P. Alukal, an assistant professor and director of reproductive health at the New York University School of Medicine, said. “A newer product, less expensive, and a new form of taking it — all that might convince more people to try it.”

Research is also under way in Brazil on a faster-acting form of the drugs, which increase blood flow by relaxing smooth muscle cells. While the existing pills enter the bloodstream indirectly by way of the stomach, intestines and liver, this form would enter more directly, dissolving in a capillary-rich space under the tongue and increasing the blood flow within 10 or 15 minutes. The research in Brazil involves generic Viagra, but Pfizer says it is not sponsoring the work.

The Mexican experiment with Viagra Jet will show whether the chewable form of the drug has promise in other countries, particularly developing markets, Susan O’Connor, Pfizer’s vice president of global commercial development, said in an interview. Studies showed most Mexican men who used Viagra ground it up to make it easier to swallow or in the belief it would start acting faster.

In explaining why the drug is being test-marketed in Mexico, Ms. O’Connor cited “patient preference, found in market research.” Mexico is the biggest market for Viagra in the developing world, with about $55 million in sales last year. At this point, Pfizer does not have plans to bring Viagra Jet to the United States, she said.

In America, Pfizer is battling to keep low-price generic competition off the shelves a year from now, when the drug’s patent expires. The generic pills would cost only a fraction of the $10 or more that each pill now costs.

Bayer, meanwhile, has introduced the dissolvable form of its Levitra drug in Austria, France, Hungary, Germany, Spain, Poland, Sweden, Denmark and Britain, where it went on sale in late March. The drug is called Levitra ODT, for orodispersible tablets. It comes in a thin black package the size of a half-dozen stacked credit cards, with four pills on a card that slides out.

“It’s pocket-friendly, discreet and gives the product a playful edge over its competitors,” Thomas Proske, global brand manager for Levitra at Bayer Healthcare, said in a statement.

The same pill was approved in the United States last June under the brand name Staxyn.

It will be available in pharmacies this month, according to Jess Macnaught, marketing executive with Burgopak Design and Packaging, the London company that designed the new black package. GlaxoSmithKline and Merck have licensed American rights from Bayer, but they declined to reveal when the drug would be introduced. Last year, they said Staxyn would reach the market in late 2010.

Worldwide sales of erectile dysfunction drugs grew 6.9 percent in 2010, to about $5 billion, and 4.7 percent in 2009, according to the industry data firm IMS Health.

Dr. Alukal of New York University said he thought Staxyn could be sold for a much lower price than what Levitra and other pills now cost, in part to compete with a generic Viagra. No price has been revealed.

“I guess it could be easier to ingest, so it could expand its market somewhat, but in the end the bigger issue would be cost,” Dr. Alukal said. He said the companies, for whom he does not consult, had talked about lower pricing, perhaps to under $10 a pill.

But for now, Pfizer, the company that started it all, is focusing its attention on protecting the pricing power and brand integrity of Viagra.

Patrick Ford, a former F.B.I. agent who leads the company’s security operations in the Americas, says Viagra is the most counterfeited product in the world. His agents pose as buyers, collect evidence and bring fraud cases to prosecutors, and he says fake Viagra may be unsafe. Pfizer and other pharmaceutical companies are working with Victoria Angelica Espinel, the government’s intellectual property enforcement coordinator, a position President Obama appointed her to in 2009.

Pfizer is also using its legal firepower against would-be generic competitors. Pfizer has two patents for Viagra, one for its chemical, expiring in 2012, and the other for its use against impotence, expiring in 2019. Pfizer sued Teva Pharmaceutical Industries, the biggest generic-drug company, in March 2010 under the “use” patent. The suit is pending in a Virginia federal court.

MacKay Jimeson, a Pfizer spokesman, said the company was confident it would keep the 2019 patent protection, but industry analysts disagree.

“ ‘Use’ patents are not highly probable of being upheld in court,” said C. Anthony Butler, a Barclays Capital pharmaceuticals analyst. “Most if not all analysts assume the expiry of the drug upon expiry of the composition of matter patent.”

The chemical patent expires on March 27, 2012. Pfizer may be able to extend it another six months, to September 2012, under a federal law called the Best Pharmaceuticals for Children Act. The law is meant to encourage drug companies to study children’s uses, often a difficult and unprofitable area.

In this case, what would be studied is not Viagra for children, but Revatio, a formulation of the same chemical, sildenafil, which is approved for pulmonary arterial hypertension, a rare and dangerous condition affecting hundreds of children in the United States. Mr. Jimeson said the company was working closely with the Food and Drug Administration to discuss the pediatric studies of Revatio and the potential for an extension on the chemical patent, which would also protect Viagra and its prices.

Many men, though, have waited years for a lower-priced Viagra and their wish may come true next year.

Other researchers are testing new uses for Viagra that Pfizer says it is not financing. Boston University is studying it with testosterone gel in men 40 to 70. Laboratório Teuto Brasileiro, in Brazil, where the patent expired last year, has filed a notice of intent to test it in a tablet that dissolves under the tongue and has an effect in 10 minutes or so. Pfizer owns 40 percent of the lab but says that it did not initiate the study.

Eli Lilly, meanwhile, says it has no plans to try chewable or dissolvable or any other forms of its Cialis tablets, and why should it? Cialis sales have steadily increased since it was introduced in 2003, to $1.7 billion last year, close to Viagra’s $1.9 billion. The health care investment house Leerink Swann estimates that Cialis sales will edge past Viagra in 2011 and far surpass the iconic blue pill in 2012.

Shawn Heffern, Lilly’s United States marketing director for Cialis, says, “I couldn’t be more happy.”