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NHLBI Cans Sildenafil Study After Reports of Severe Pain

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The National Heart, Lung, and Blood Institute (NHLBI) announced, on Tuesday, that it was ending a clinical study involving Pfizer’s Revatio (sildenafil), a hypertension treatment and the active ingredient in Viagra, due to safety concerns.

According to a lengthy release from the Institute, researchers realized that the patients in the study for the treatment of pulmonary hypertension in adults with sickle cell disease were more likely to be hospitalized for severe pain than patients taking the placebo.  Pulmonary hypertension occurs in patients with blocked or constricted arteries in the lung, which could lead to heart failure.

The study, called “walk-PHaSST,” was stopped one year into testing, and no deaths have been attributed to the treatment in this trial. The NHLBI stated that 38 percent of the patients taking the medication showed side effects, including sickle cell pain.

“The increase in sickle cell medical problems is concern enough for us to stop this clinical trial to protect the safety of our participants,” said NHLBI Director Elizabeth Nabel. “We will continue to look into the possible causes of these preliminary results. In the meantime, we encourage patients with sickle cell disease who are taking sildenafil for pulmonary hypertension to talk with their physicians about the potential risks and benefits of the medication.”

Revatio is approved for the treatment of pulmonary arterial hypertension. According to Pfizer’s brand site, the drug allows blood vessels and muscles to relax, causing blood and oxygen to flow more freely. Side effects include sudden vision loss and diarrhea at dosages above the recommended 20 mg.

Patients currently taking Viagra or Revatio for their approved uses should not be concerned.

Pfizer told CNN that it’s working with the NHLBI to find out why these events happened and will look at existing data that it has on the treatment. “Revatio has a well-established safety profile for its approved indication, pulmonary arterial hypertension,” the company stated.

“Although these preliminary results are disappointing, we expect that the study’s results, once fully analyzed, will provide important insights into the role of pulmonary hypertension in sickle cell disease,” said Mark Gladwin, lead investigator for walk-PHaSST.

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