The National Institutes of Health (NIH) said on Tuesday it had halted a trial of the drug sildenafil for patients with sickle cell disease, saying the drug caused serious medical problems.
The trial was testing the safety and effectiveness of sildenafil, sold by Pfizer as Viagra and Revatio, as a treatment for pulmonary hypertension in patients with sickle cell disease, said the National Heart, Lung, and Blood Institute (NHLBI).
Patients without sickle cell disease taking the sildenafil — which is approved under the Revatio brand name to treat pulmonary hypertension in otherwise healthy adults — are not at risk, the NHLBI added.
The researchers found that 38 percent of patients taking Revatio had serious adverse effects such as painful sickle cell “crises”, compared with just 8 percent of patients taking a placebo.
“The increase in sickle cell medical problems is concern enough for us to stop this clinical trial to protect the safety of our participants,” NHLBI Director Dr. Elizabeth Nabel told Reuters.
“We will continue to look into the possible causes of these preliminary results,” she added.
“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 and what actions they should consider, including whether to taper off this medication and how to best manage both sickle cell disease and pulmonary hypertension.”
“No deaths have been associated with the drug in the clinical trial,” said the NHLBI said in a statement.
Pulmonary hypertension is high blood pressure within the arteries that carry blood to the lungs. The condition can cause heart failure and death. Sildenafil treats pulmonary hypertension by relaxing the blood vessels in the lungs so the blood can flow more easily.
Roughly 30 percent of those with sickle cell disease develop pulmonary hypertension, which can cause sudden death.
The U.S. Food and Drug Administration (FDA) has not approved sildenafil to treat pulmonary hypertension in patients with sickle cell disease, so the NHLBI was conducting a small trial to see if the drug would help these patients.
Sildenafil is currently sold under the name Viagra as a treatment for erectile dysfunction or impotence.
Shares of Pfizer were down 3.55 percent on Tuesday, closing at $16.03 on the New York Stock Exchange.
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