General Information

Tracleer tablets have been approved by the FDA for the treatment of pulmonary arterial hypertension (PAH). This drug is indicated for use in improving exercise ability and decreasing the rate of clinical worsening in patients with WHO Class III or IV symptoms. Tracleer 125 mg (taken twice a day) is the first approved oral treatment for patients with PAH.

Tracleer belongs to a class of drugs known as endothelin receptor antagonists (ERAs). Patients with PAH have elevated levels of endothelin, a potent blood vessel constrictor, in their plasma and lung tissue. Tracleer blocks the binding of endothelin to its receptors, thereby negating endothelin's deleterious effects.

Clinical Results

Results of a pivotal trial known as BREATHE-1 (Bosentan: Randomized Trial of Endothelin Receptor Antagonist THErapy) supported the approval of Tracleer. In the 213-subject trial, Tracleer (125 mg b.i.d. and 250 mg b.i.d.) was administered on a twice-daily basis. For both primary and secondary PAH, results showed statistically significant improvements versus placebo in the primary efficacy endpoint, exercise capacity. The overall treatment effect for both doses of Tracleer combined was a 44-meter improvement in walking distance compared to placebo (as measured by a six-minute walk test). Tracleer also produced a significant delay in time to clinical worsening, defined as death, hospitalization, worsening PAH or initiation of intravenous therapy. Lastly, treatment with Tracleer resulted in significant improvement in functional status and breathlessness.

Side Effects

Adverse reactions reported in clinical testing of Tracleer include (but are not limited to) the following:

Headache

Nasopharyngitis (inflammation of the nose and pharynx)

Flushing

Edema, lower limb

Hypotension

Palpitations

Women who are pregnant, or who may become pregnant, should not take Tracleer due to the risk of birth defects. Additionally, patients receiving Tracleer should undergo monthly liver monitoring to ensure that proper enzyme levels are maintained.

Mechanism of Action

Endothelin-1 (ET-1) is a neurohormone, the effects of which are mediated by binding to ETA and ETB receptors in the endothelium and vascular smooth muscle. ET-1 concentrations are elevated in plasma and lung tissue of patients with pulmonary arterial hypertension, suggesting a pathogenic role for ET-1 in this disease. Bosentan is a specific and competitive antagonist at endothelin receptor types ETA and ETB . Bosentan has a slightly higher affinity for ETA receptors than for ETB receptors (from Tracleer Prescribing Information).