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Update: Docs Release More Findings in Thelin PH Drug Trial
by John C. Martin
06-09-05 - Researchers at a California medical conference last month unveiled more findings of a pivotal Phase 3 clinical trial testing the safety and efficacy of an investigational medication for pulmonary arterial hypertension.1 The trial is one of the bases for a pharmaceutical manufacturer's move to seek approval of the drug from the U.S. government.
A Hidden Cause
Pulmonary hypertension is a rare lung disorder in which the blood pressure in the pulmonary artery which runs from the heart to the lungs rises far above normal levels. The reason is still unknown. This abnormally high blood pressure, in turn, leads to abnormal changes in the small blood vessels in the lungs. Increased resistance to blood flowing through the vessels results, placing a strain on the heart's right ventricle, eventually leading to right-heart failure, and possible death. In the United States, about 500 to 1,000 new cases of primary pulmonary hypertension are diagnosed each year. More women than men are diagnosed, according to estimates, and it's most commonly found in those between ages 20 and 40.2
Comparing Thelin to Placebo
The trial, lasting 18 weeks, put the drug Thelin, also known by its generic name sitaxsentan, to the test in a group of 246 patients with the disease. The participants were assigned at random to groups receiving one of two doses of the medication, or a group given a placebo as a comparison. A group in the study also received the already approved PH drug, Tracleer (bosentan), to compare the results.
The study investigators reported Thelin improved the distance that patients were able to walk in a standard 6-minute test. This was seen particularly in those taking 100 mg doses. Their walking distance increased "significantly", according to the drug's maker, Encysive Pharmaceuticals, by an additional 31 meters (34.3 yards) versus those on placebo.
By contrast, those taking Tracleer increased their walking distance in 6 minutes by about 29 meters (32.3 yards), the study team reported. While that was also a positive finding, it was later found that starting at week 12 of the study, those taking 100 mg of Thelin continued to improve, whereas those taking Tracleer "trended down". Thelin also improved function (based on WHO criteria) compared to placebo, but Tracleer did not, the investigators noted.
Patients were also assigned 50-milligram doses of the drug, but the investigators said the findings in that group were not significant. Thus, Encysive says it doubts the drug will be made available to patients at this dose.
Encysive Seeks FDA Endorsement
"We are very pleased with the clinical results of our second-generation, selective endothelin antagonist, whether compared to placebo or to bosentan, the only approved oral product for pulmonary arterial hypertension," said Bruce Given, MD, Encysive's President and CEO, in a company press release. "Data from [this trial] and our other Phase 2 and 3 studies form the basis of our New Drug Application", which was scheduled to be filed in May.
Side effects reported in trials of Thelin include headache, edema (fluid build-up), nausea, upper respiratory tract infection, dizziness, insomnia, nasopharyngitis, and nasal congestion.3
1. ATS 2005. The International Conference of the American Thoracic Society. 2005 May 20-25. San Diego, CA.
2. American Heart Association. Primary or Unexplained Pulmonary Hypertension. Available at: http://www.americanheart.org/presenter.jhtml?identifier=4752. Accessed June 9, 2005.
3. Barst RJ, Langleben D, Frost A et al. Sitaxsentan therapy for pulmonary arterial hypertension. Am J Respir Crit Care Med 2004 Feb 15;169(4):441-7. Epub 2003 Nov 20.
John Martin is a long-time health journalist and an editor for Priority Healthcare. His credits include overseeing health news coverage for the website of Fox Television's The Health Network, and articles for the New York Post and other consumer and trade publications.
Drug study news about Thelin and pulmonary hypertension.
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