LOS ANGELES (Reuters) - Pfizer Inc. said on Saturday that new trial data show that its inhaled version of insulin, recently approved by regulators, safely controls blood sugar over a two-year period.

The world's largest drugmaker expects to launch Exubera in the United States next month after receiving U.S. Food and Drug Administration approval in January to market the product for adults with either Type 1 or Type 2 diabetes.

Industry analysts have forecast that sales will top $1 billion a year as millions of Americans who now rely on injected insulin to control their diabetes replace at least some of their shots with the short-acting powder form.

The company said two ongoing trials show that patients using Exubera experienced sustained blood sugar control over a two-year period and gained about half as much weight as those using injected insulin.

"There are a lot of physical barriers to injected insulin. This (Exubera) is a good tool to facilitate initiation of insulin treatment," said Dr. Julio Rosenstock, trial investigator and director of the Dallas Diabetes & Endocrine Center.

He leads a study involving 635 adults with type 2 diabetes being treated with injected insulin, who were then randomized to either Exubera or continued injections.

After two years, patients in both groups had similar improvement or maintained their blood sugar levels. Weight gain in patients taking Exubera was 1.7 kg (3.7 pounds), compared to 3 kg (6.6 pounds) in patients on injected insulin.

Coughing was more frequent in the Exubera group, but it was mostly mild and temporary, Rosenstock said, noting that just 2.2 percent of patients dropped out of the trial due to the side effect.

Lung function, which declines as people age, dropped by about 1.5 percent more in the Exubera group than it did in patients on injected insulin.

"The findings in terms of safety were very reassuring. The drop in pulmonary function was nonprogressive and reversible," Rosenstock said.

A second study, involving 582 adults with type 1 diabetes, also showed that after two years of treatment, patients improved or maintained their blood sugar control.     In this trial, Exubera patients gained an average of 0.8 kg (1.7 pounds), compared with 2 kg (4.4 pounds) for patients on injected insulin.

Both trials, results of which were presented in at a Washington, D.C., meeting of the American Diabetes Association, will continue for another 5 years, said Dr. David Simmons, Pfizer's U.S. medical director for Exubera.

He estimated that nearly 15 million Americans have been diagnosed with diabetes, which if left unchecked can cause heart disease, amputation, blindness, kidney failure and death.

"Many patients who need insulin aren't getting it. This is a revolutionary product," Simmons said.

In patients with Type 2 diabetes, Exubera can be used alone or in combination with diabetes pills or longer-acting insulin. In patients with Type 1 diabetes, Exubera should be used in combination with a longer-acting insulin.

It should not be used by smokers, people with underlying lung disease, or pregnant women.

Pfizer and drug delivery company Nektar Therapeutics developed Exubera, which is also approved for sale in Europe. The company launched sales last month in Germany and Britain at a price up to 3.5 times that of injected insulin.