Ambrisentan Treatment for Pulmonary Arterial Hypertension

Ambrisentan is a vasodilator drug that has been developed by Myogen for the treatment of pulmonary arterial hypertension (PAH). Ambrisentan is in the midst of ongoing phase III clinical trials testing the safety and efficacy of the PAH drug.

Pulmonary arterial hypertension is a deadly type of lung disease that is characterized by a higher-than-normal blood pressure in the pulmonary artery (exceeding 25 mmHg). PAH is often referred to as primary pulmonary hypertension (PPH), instances of which can cause the gradual degrading of the heart and lungs, culminating in patient death.

Ambrisentan has been manufactured with the initial aim of serving as a viable drug treatment for people suffering from PAH; however, it is viewed to have a future in the treatment of a variety of diseases requiring the regulation of vascular constriction.

Ambrisentan Treatment - Mechanism of Action

Ambrisentan is an endothelin receptor antagonist drug that blocks the action of endothelin, a very potent, naturally occurring vasoconstrictor that is capable of causing severe narrowing of the blood vessels.

Studies show that endothelin is present in larger amounts in patients suffering from PAH. There are two types of naturally occurring endothelin receptors: ETA and ETB. When endothelin binds with ETA receptors, it causes the narrowing of the blood vessels (vasoconstriction). When endothelin binds with ETB receptors, it produces nitric oxide and prostacyclin, relaxing and widening the blood vessels (vasodilation). The ETB receptors exist to counteract the ETA receptors and prevent against excessive narrowing of the blood vessels.

Ambrisentan is one of several newly developed vasodilator drugs that specifically target the ETA receptors, inhibiting their action and preventing vasoconstriction. Although Ambrisentan remains in the clinical trial process awaiting FDA approval, it is expected to function as a once-a-day oral medication.

Ambrisentan Side Effects

Ambrisentan is expected to provide optimal results in the treatment of PAH once the endothelin receptor antagonist has been approved for widespread use by the FDA. However, like all drugs, there are certain side effects that can be expected when undergoing Ambrisentan drug treatments, the most common of which is the occurrence of a headache. Ambrisentan patients also face the risk of developing liver function abnormalities; thus far, there has been a low incidence of this side effect in clinical trial testing.

Ambrisentan Clinical Trial Testing

The Ambrisentan Phase II Clinical Trial was a randomized dose-ranging study that included a total of 64 patients suffering from pulmonary arterial hypertension. The phase II trial involved four groups, each being administered a different dose of Ambrisentan on a daily basis for a 12-week period; groups were given 1.0 mg, 2.5 mg, 5.0 mg or 10.0 mg of Ambrisentan.

Phase II of the Ambrisentan clinical trial concluded in September of 2003. From the results, Myogen reported that Ambrisentan appears to be a safe and effective drug in the treatment of PAH.

Ambrisentan phase III clinical trials were initiated in January of 2004 so as to further evaluate the safety and efficacy of the endothelin receptor antagonist drug in the treatment of PAH. The placebo-controlled phase III trials are expected to end sometime in 2006.

PAH Drugs - Ambrisentan vs. Thelin

Ambrisentan and Thelin are two newly developed PAH drugs that are currently awaiting FDA approval. Initially, it appeared that Ambrisentan would be approved roughly one to two years after Thelin because the latter's clinical trials began earlier. However, the FDA posed additional questions regarding the safety and efficacy of Thelin to the drug's manufacturer, Encysive Pharmaceuticals Inc., delaying its approval. As a result of this delay, Ambrisentan could potentially be released to consumers prior to Thelin, gaining a stranglehold on the market share that was assumed to be reserved for Encysive's endothelin receptor antagonist.

Regardless of which drug receives FDA approval first, both are expected to provide beneficial results in the ongoing treatment of pulmonary arterial hypertension.

Last Revision: September 9, 2013