NEW YORK (Dow Jones)--Pfizer Inc's (PFE) Revatio, which is identical to Viagra but in different dosage, missed the main goal of a study in an advanced form of a fatal lung disease, although improvements in some symptoms may aid patients that currently have no options.

The study, published in The New England Journal of Medicine, comes just two weeks after the Food and Drug Administration rejected InterMune Inc.'s (ITMN) pirfenidone as the first treatment for the condition, called idiopathic pulmonary fibrosis, which usually kills patient within a few years. Unlike pirfenidone, Pfizer's drug is available on the market and could potentially be used by physicians who can prescribe FDA-approved drugs in any way they see fit.

The researchers who conducted the study concluded that the symptomatic improvements were "no doubt important to patients, especially those with disease as severe as the ones we enrolled", in light of there being no treatments.

The study was conducted by the National Heart, Lung, and Blood Institute, which is part of the National Institutes of Health. Pfizer donated the drug and placebo for the trial.

Viagra, which brought $1.9 billion in sales 2009, is also sold as Revatio, which had $450 million in sales last year. The latter is sold as a treatment for pulmonary arterial hypertension, which is high blood pressure in the pulmonary arteries that makes patients susceptible to heart failure. The published study used Revatio, which is 20 milligrams of the compound taken three times a day.

The drug, with a generic name of sildenafil works by dilating some of the body's key blood vessels, so the researchers hypothesized that improving blood flow in functioning portions of the lungs would improve respiration.

Idiopathic pulmonary fibrosis involves the scarring of the lungs, often from an unknown cause, which makes it hard for oxygen to enter the blood.

About 200,000 Americans have the condition, with about 50,000 new cases every year, according to the National Institutes of Health. It mostly affects people between 50 and 75 years old, and patients generally live three to five years after diagnosis.

In the study, 180 patients with an advanced stage of the disease were split into two groups to either receive Revatio or a placebo for 12 weeks.

The data showed that the drug didn't achieve its main goal of a 20% improvement in the distance walked by patients in six minutes. But it did show improvements in lung function, shortness of breath and quality of life among those taking the drug.

After 12 weeks, patients who were initially on placebo were switched to Revatio, with their knowledge, for 12 weeks. Those patients didn't achieve an improvement in walking distance or in other symptoms.

The researchers note that the improvements in symptoms in the first stage of the study were "of a magnitude that other observers have found to be clinically meaningful."

They warned that the study was limited by factors including its size, duration and inclusion of only advanced patients. Serious side effects were similar in both arms of the study.

Although it failed to meet its main goal, the study concludes that the benefits of Revatio in the disease are uncertain and warrant further clinical trials.

"While such trials are being designed and implemented, our finding that sildenafil was associated with symptomatic improvement may be of value to patients with advanced idiopathetic pulmonary fibrosis," the researchers wrote.