(AP) -- Drugmaker Pfizer Inc. said Thursday that the European commission has approved treating children with its medicine for a rare, deadly lung condition - a drug better known as Viagra.

The drug, Revatio, was approved in Europe about six years ago for treating adults with what's called pulmonary arterial hypertension, or in lung arteries. Now it can be given to children aged 1 to 17.

The medicine is better known as Viagra, the erectile dysfunction drug that quickly became a blockbuster for New York-based after it was approved in 1998.

Viagra, known chemically as sildenafil citrate, was originally developed to treat blood pressure problems. But when some men participating in clinical tests reported a welcome but unexpected side effect - better erections - researchers switched tracks and began focusing on it as an impotence treatment.

Viagra has since brought Pfizer many billions of dollars. It now generates close to $2 billion in annual sales, despite fierce competition from two heavily advertised rival pills, Levitra and Cialis.

A recent study in children found the formulation in Revatio reduced blood pressure in lung arteries and helped them breathe and function better.

Revatio is approved for adults with the lung condition in more than 50 countries, including the United States. Pfizer is now seeking approval in numerous countries for treating children with .

The rare, leads to and premature death. Its cause can't always be determined.

"These young patients now have an important treatment option that may help manage their condition," Dr. Cara Cassino, head of Pfizer's medicines development group, said in a statement.

In the 234-patient study that led to the new European approval, side effects were similar to those in adults, including vomiting, nausea, fever, cough, abdominal pain and extreme .

©2011 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.