Pfizer Inc., the world’s biggest drug maker, plans to use television commercials to pitch the first inhaled insulin treatment directly to diabetics after the product failed to catch on with doctors.

Approved by the U.S. Food and Drug Administration in January 2006, the drug, called Exubera, has been largely spurned by diabetes specialists, generating only about $5 million in sales last year, or one-tenth as much as some analysts forecast. Pfizer will start the advertisements in the second half of this year.

Ads also are scheduled for magazines as part of a marketing strategy designed to overcome the product’s higher cost and the inconvenience of the device used to administer the drug, analysts say. The New York-based drug maker, which employs more than 300 Rhode Islanders at the company’s world headquarters for research and development in New London and Groton, Conn., is risking criticism by members of Congress and physician groups who say consumer advertising encourages excessive use of costly therapies.

“Pfizer is now putting on a full-court press, creating an expectation” with the ad campaign that “prescriptions should start going up,” Jim Reddoch, an analyst with Freidman, Billings, Ramsey & Co. in Arlington, Va., said in a research report.

Doctors say the inhaler, as big as a half-liter bottle, is unwieldy and patients can pay about $600 a year more for Exubera than injectable forms of insulin, under certain health plans. Clinical trials have found that the product can reduce lung function for some patients. Pfizer says the condition is reversible and is conducting a five-year study among users to monitor it.

Some analysts reduced by 50 percent their 2010 sales estimates, which had reached as high as $1.8 billion when the drug was first approved. Pfizer wants Exubera to help offset revenue that will be lost when several big-selling medicines no longer have patent protection.

Pfizer’s 2006 earnings more than doubled, to $19.3 billion, or $2.66 a share, from the year before. The company’s share price fell 20 cents to $25.87 yesterday in New York Stock Exchange composite trading and has fallen 1.2 percent in the past 12 months.

“I’ve brought it up to a few patients, and many just aren’t that interested in it,” Christopher Saudek, a professor of medicine at Johns Hopkins University who specializes in diabetes, said of Exubera. “It is a cumbersome device.”

The television ads will target newly diagnosed diabetics who may not want to inject themselves daily, said Ian Read, president of Pfizer’s worldwide pharmaceutical operations. Patients who develop diabetes later in life may put off using insulin because of needle phobia, he said.

“The heart of the issue in diabetes therapy is the delay in getting patients to begin taking insulin, a delay that often lasts more than eight years,” Read said.

About 14.6 million Americans are diagnosed with diabetes, according to the American Diabetes Association. In the disease, the pancreas either doesn’t produce enough of the hormone insulin or the body doesn’t properly use it. Cells require insulin to turn glucose, or blood sugar, into energy. Untreated, diabetes can lead to blindness, kidney disease, nerve damage and risk of heart attacks and strokes.

Pfizer chief executive officer Jeffrey Kindler said at a January analysts’ meeting that it will take longer than 2010 to reach a goal of $1.9 billion in peak annual sales. Pfizer is testing smaller inhalers, although they probably won’t become available until at least 2010, analysts said.

Pfizer needs to spur Exubera sales because Indianapolis-based Eli Lilly & Co. and Denmark’s Novo-Nordisk A/S are testing insulin inhalers that are smaller and less complex, analysts say.

Pfizer, which once expected to introduce Exubera by 2002, delayed seeking approval for the device for four years after finding a 1-percent reduction of patient lung function in a trial. While Pfizer has since said any impact on the lungs appears to be reversible, doctors are required to test patients to avoid giving it to those with reduced capacity.

The drug’s packaging also says the product shouldn’t be used by smokers because that interferes with the lung’s ability to absorb insulin.

Pfizer also was forced to delay marketing the drug to primary-care doctors by several months after last year’s approval because the new technology used to make the product wasn’t initially able to produce large quantities, the company said in an October regulatory filing.

Insurance coverage is another impediment, doctors say. Exubera costs patients $616 more a year than Lilly’s Humalog insulin injection pen under certain insurance plans that provide coverage for recipients of Medicare, the health plan for the elderly.

“Insurers are trying to push people towards cheaper insulin,” said Richard Hellman, president-elect of the American Association of Clinical Endocrinologists. “There are many people who would welcome it if it wasn’t for the cost.”

Some 2,300 Pfizer sales representatives have been promoting Exubera to more than 5,000 doctors. Analysts say they are skeptical that consumer ads will produce better results.

“We are not aware of any pharmaceutical product that has ever become a blockbuster that was not endorsed by specialists,” says Merrill Lynch analyst David Risinger, who last month lowered his initial 2008 sales projection to $175 million from $300 million.