Myogen's Ambrisentan granted orphan drug designation by Europeans

May 2 2005

Myogen today announced that the Commission of the European Communities, with a favorable opinion of the Committee for Orphan Medicinal Products of the European Medicines Agency (EMEA), has granted orphan drug designation to ambrisentan for the treatment of pulmonary arterial hypertension (PAH) and chronic thromboembolic pulmonary hypertension.

In August 2004, Myogen announced that the United States Food and Drug Administration (FDA) granted orphan drug designation to ambrisentan for the treatment of PAH. Myogen is currently evaluating ambrisentan for the treatment of patients with PAH in two pivotal Phase 3 trials, ARIES-1 & -2.

Regulation (EC) No 141/2000 of the European Parliament and of the Council of the European Union of 16 December 1999 on orphan medicinal products is intended to introduce incentives for research, development and marketing of medicinal products for the prevention, diagnosis and cure of rare diseases and disorders, in particular by granting exclusive marketing rights for a ten-year period. Orphan medicinal products have access to protocol assistance and the "centralized" marketing procedure. The sponsor of an orphan medicinal product can be exempted from payment of the fees payable to the EMEA. Marketing exclusivity does not prevent the marketing of similar medicinal products if the holder of the marketing authorization of the original orphan product gives consent to the other applicants or is unable to supply sufficient quantities of product, or if another product proves safer, more effective or otherwise clinically superior to the first. Orphan medicinal products can be eligible for further incentives made available by the European Commission and the individual member countries to support the research, development and availability of orphan medicinal products.

Ambrisentan is a type-A selective endothelin receptor antagonist and potent inhibitor of endothelin-induced vasoconstriction. Endothelin is a small peptide hormone that is believed to play a critical role in the control of blood flow and cell growth. Elevated endothelin blood levels are associated with several cardiovascular disease conditions, including pulmonary arterial hypertension, chronic renal disease, coronary artery disease, hypertension and chronic heart failure. Therefore, the company believes that agents that block the detrimental effects of endothelin may provide significant benefits in the treatment of these conditions. Ambrisentan is selective for the ET(A) receptor versus the ET(B) receptor and demonstrates a half-life that may be suitable for once a day dosing.