Sitaxsentan (Thelin): Pulmonary Arterial Hypertension Treatment

Thelin has been granted Orphan drug status by the FDA, which gives the drug maker a seven year exclusivity once the medication is approved, The Food and Drug Administration grants orphan-drug status to therapies aimed at treating diseases and disorders affecting fewer than 200,000 people in the United States.

Sitaxsentan (Thelin) is an experimental treatment being tested by Encysive Pharmaceuticals to treat pulmonary hypertension. It is in a class of drugs called endothelin antagonists. Endothelin is a hormone which attaches to endothelin receptors in blood vessels causing them to narrow. Endothelin becomes more abundant in pulmonary hypertension and is believed to be the cause of the disease. By blocking the endothelin receptors, Sitaxsentan reverses the narrowing effect of pulmonary hypertension and assists blood flow.

One of the major draw backs of the endothelin antagonist class of drugs is their tendency to cause liver abnormalities. The hope for Sitaxsentan is that it will demonstrate relatively low liver toxicity and provide an effective alternative to other endothelin antagonists.

Encysive Pharmaceuticals recently concluded a Phase III clinical trial study that tested STRIDE (Sitaxsentan To Relieve Impaird Exercise) in patients with Pulmonary Arterial Hypertension. The study was a twelve week clinical trial involving 178 patients. The patients were divided into three categories: those receiving placebos, those receiving 100 mg of Sitaxsentan and those receiving 300 mg of Sitaxsentan.

The primary goal of the trial was to test how well Sitaxsentan increases breathing capacity. The secondary goal was to determine how well it affects exercise tolerance. i.e. the patients ability to walk a 6 minute distance.

The results were somewhat promising. Patients receiving the 300 mg treatments showed a 7% improvement in breathing capacity as compared to those taking the placebo, while patients taking the 100 mg treatments showed no improvement. However, both the patients taking 100mg and the patients taking 300mg showed a 9% improvement in exercise tolerance. Generally both dosages were found to ease pulmonary circulation and have beneficial therapeutic effects.

Of all the patients that participated in the trial, none of the patients taking 100mg dosage were required to stop their treatment either because of adverse effects or for other reasons, versus seven patients from the 300 mg group, and five from the placebo group. The most common side effect suffered by the patients being treated with Sitaxsentan were peripheral edema, head aches, dizziness and nasal congestion.

Predictably the 300 mg dose was found to be riskier in terms of liver toxicity with reversible liver abnormalities occurring in 9.5 % of the patients in this group. While less liver abnormalities (0%) occurred in the 100 mg group than the placebo group (3%). Overall, researchers felt that the 100 mg dose would be a more appropriate choice for the Pulmonary Hypertension patient in most cases. However, for more severely impaired patients researchers felt that the additional cardiopulmonary reserve offered by a larger dose may tip the scales in favor of the 300 mg dose.

Thelin once approved will compete with two similar drugs, Tracleer already widely used and the yet to be approved Ambrisentan.


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Although Pulmonary Hypertension cannot be cured using existing medicine. It can be controlled with new drugs and therapies.

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