NEW YORK (CNN/Money) - The Food and Drug Administration approved Revatio, a treatment for pulmonary arterial hypertension that uses the same active ingredient as Viagra, said Pfizer Inc. on Monday.

However, Pfizer won't get a big lift in sales from Revatio, because the target population is relatively small and some of those patients are already using Viagra to treat pulmonary arterial hypertension, or PAH, according to Pfizer and analysts.

"[Revatio] is not a big revenue maker," said Pfizer spokesman Daniel Watts. "We felt that it was worth pursuing from a clinical standpoint. We certainly didn't promote it, but there were some reports that it was being used off-label."

Barbara Ryan, analyst for Deutsche Bank North America, projected that Revatio will make $200 million in annual sales by 2008. Ryan said this is "not a big deal" for Pfizer, the world's largest drug company with $52.5 billion in 2004 sales.

The active ingredient, sildenafil citrate, would be used in Revatio to fight a rare, aggressive and life-shortening vascular disease, known as PAH, which affects about 100,000 people worldwide. Untreated patients with PAH, which causes high pressure in blood vessels leading from the heart to the lungs, have an average survival time of less than three years following diagnosis, the company said.

Sildenafil citrate is also the ingredient in Viagra, an erectile dysfunction drug also made by Pfizer and used by more than 26 million men worldwide. Viagra sales totaled $1.7 billion in 2004.

Revatio is expected to enter the market in mid-July, said Watts, but for some PAH patients it will merely legitimize the use of sildenafil citrate in treating their disease.

"We believe that some [PAH] patients are already using the active ingredient for pulmonary arterial hypertension," said Robert Hazlett, analyst for Suntrust Robinson Humphrey.

Pfizer (up $0.05 to $28.01, Research) stock prices moved only slightly following the pre-market announcement.

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The analysts interviewed for this story do not own Pfizer stock. An affiliate of Suntrust received money from Pfizer and Deutsche Bank NA owns Pfizer stock.