TUESDAY, Oct. 25 (HealthDay News) -- New research suggests that the active ingredient in the erectile dysfunction drug Viagra, which was initially developed as a treatment for heart disease, could help children with a rare condition called pulmonary arterial hypertension.

The drug, which is expensive to take regularly and has side effects, is already approved to treat the condition in adults. And some pediatricians use it to treat children, said Dr. Thomas Kulik, senior associate in cardiology at Children's Hospital Boston. But it has not yet received U.S. Food and Drug Administration approval for that purpose.

Pulmonary arterial hypertension, a rare condition, causes abnormally high blood pressure in the arteries that lead to the lungs. It can be inherited, accompany some forms of heart disease or occur for no known reason, Kulik said. The disease can limit the ability to exercise and lead to heart failure or even death.

In adults, research has shown that sildenafil -- best known by the brand name Viagra -- can help improve oxygen delivery and exercise tolerance, but it's not clear if it improves lifespan, said Kulik, who is also an associate professor of pediatrics at Harvard Medical School in Boston.

In the new study, researchers gave a placebo or low, medium or high doses of sildenafil to children aged 1 to 17 years for 16 weeks. After that time, they tested 105 of the children.

Previously, study author Dr. Robyn Barst of Columbia University in New York City led research that found that the active ingredient in another erectile drug, Cialis (tadalafil), seemed to effectively treat pulmonary hypertension in adults.

In the new study, researchers found that that children who took the drug and could exercise at the end of the study had more improvement in lung function than those who took the placebo. The researchers, including two from Pfizer, manufacturer of Viagra, also found that the children could exercise more and with greater ease.

Kulik, who is familiar with the findings but was not involved with the study, said the effect was modest at best. Still, he said, "sildenafil probably somewhat increases the ability of pediatric patients to exercise."

In adults, he said, the drug can cause vision problems, and in kids it can cause a condition called priapism, in which the penis remains erect. Lowering the dose can eliminate the problem, he said.

Overall, a medium dose appears safest and most effective, the researchers said, but still more research is needed. Kulik said it will take some time to determine if it improves lifespan for children with the condition.

The drug can cost several thousand dollars a year, he said.

The study was scheduled to be released Tuesday at the American College of Chest Physicians annual meeting, in Honolulu.

Research presented at meetings is considered preliminary until published in a peer-reviewed medical journal.

More information

To learn more about pulmonary arterial hypertension, visit the U.S. National Library of Medicine.