US pharmaceutical giant Pfizer announced on Friday it is pulling its blood pressure drug Thelin off the market due to a potentially life-threatening risk of liver damage.
Pfizer said it was voluntarily withdrawing Thelin in the European Union, Canada and Australia and is also suspending all clinical tests on the drug that treats pulmonary arterial hypertension (PAH), a rare, incurable disease that can result in heart failure and early death.
"While liver toxicity is a known complication of the class of drugs to which Thelin belongs, a new potentially life-threatening idiosyncratic risk of liver injury with Thelin has been observed," Pfizer said in a statement.
"Given the availability of alternate treatments, Pfizer has concluded that the overall benefit of Thelin no longer outweighs the risk in the general population of PAH patients."
The company said it had notified health authorities about its findings and its decision to withdraw Thelin from the market and stop clinical studies.
"Patients taking Thelin or participating in Thelin studies are advised to consult with their health care professional as soon as possible," it said.
It added that patients should not stop taking Thelin until they speak with their doctor.
The European Medicines Agency (EMA) said it had been informed of the move and would discuss the issue at its meeting next week.
Pfizer acquired the rights to Thelin - an oral, once-daily drug - when it took over Encysive Pharmaceuticals in 2008 in a 195-million-dollar deal.
Thelin had yet to be approved by the US Food and Drug Administration, which said it was not sufficiently effective.
PAH is estimated to affect 100,000 to 200,000 people in North America and Europe, including about 55,000 in the United States.
Though rare, the disease affects men and women of all races and ages, but is more common among women aged 20 through 40. The disease may be misdiagnosed as asthma, anemia or chronic obstructive pulmonary disease.
PAH is characterized by high blood pressure and structural changes in the walls of the pulmonary arteries, the blood vessels that connect the right side of the heart to the lungs.
The pulmonary arteries become thickened and constricted, forcing the heart to work harder to pump blood through the lungs, leading to fatigue and eventually to heart failure.
Thelin acts to dilate the constricted blood vessels, thereby reducing pulmonary arterial pressure and improving the heart's performance.
Thelin sales reached 44.4 million dollars in the first nine months of this year, according to Pfizer spokesman Allen Curtis.
The news did little to Pfizer's shares, which were virtually unchanged on Wall Street at 1530 GMT.