Myogen Announces Achievement Of Target Enrollment For Pivotal Phase 3 ARIES-1 Trial Of Ambrisentan In PAH

DENVER, Nov. 10 /PRNewswire-FirstCall/ -- Myogen, Inc. , a biopharmaceutical company focused on the discovery, development and commercialization of small molecule therapeutics for the treatment of cardiovascular disorders, today announced the achievement of target enrollment of 186 patients in ARIES-1, one of the Company's two pivotal Phase 3 trials of ambrisentan in patients with pulmonary arterial hypertension (PAH). A number of additional patients are in screening and the Company will allow those patients to complete the process and either be randomized into the trial or disqualified, in accordance with the trial protocol. The Company expects to report top line results of the trial in the second quarter of 2006. In addition, as previously announced, the Company expects to report top line results of ARIES-2, the other pivotal Phase 3 trial of ambrisentan in PAH, in December of this year.

"The completion of patient enrollment in ARIES-1 is an important milestone for ambrisentan and Myogen," said J. William Freytag, President and Chief Executive Officer of Myogen. "We are gratified by the continuing support and confidence of the patients, clinical investigators and our scientific advisors participating in the ARIES trials. Based on the properties of the compound and the results of our Phase 2 trial, we believe ambrisentan's efficacy and safety profile may position it as the best-in-class among endothelin receptor antagonists. We are excited by the progress of our ambrisentan clinical program and look forward to sharing the results of the ARIES-2 trial in December."

In January 2004, Myogen initiated two pivotal Phase 3 clinical trials, ARIES-1 and ARIES-2, evaluating the safety and efficacy of ambrisentan in patients with PAH. The ARIES trials are randomized, double-blind, placebo-controlled trials of identical design except for the doses of ambrisentan and the geographic locations of the investigative sites. Both trials were designed to enroll 186 patients (62 patients per dose group). ARIES-1 evaluates once daily doses of 5 and 10 mg of ambrisentan and ARIES-2 evaluates once daily doses of 2.5 mg and 5 mg of ambrisentan. The primary efficacy endpoint is exercise capacity, measured as the mean change from baseline at 12 weeks in the 6-minute walk test compared to placebo. Secondary endpoints include time to clinical worsening, World Health Organization (WHO) functional class and Borg dyspnea index. ARIES-1 enrolled patients primarily from North America plus selected international sites, while ARIES-2 enrolled patients primarily in Europe plus selected international sites.

In September 2003, Myogen reported results of a Phase 2 clinical trial of ambrisentan in patients with PAH. To date, the results of the Phase 2 trial and related long-term trial have demonstrated:

* Significant improvements in 6-minute walk distance, Borg dyspnea index and WHO functional class * Durable efficacy with long-term ambrisentan monotherapy and a possible survival benefit * Comparable efficacy in patients with WHO functional class 2 and class 3 symptoms * Dose flexibility * True once-daily dosing * No drug-drug interactions (no p450 induction or inhibition) * No evidence of drug-drug interaction with warfarin anticoagulation * Low incidence and severity of liver function test abnormalities that do not appear to be dose related

Based on these Phase 2 clinical trial results, the Company believes ambrisentan may by useful in treating patients with PAH and may offer several clinical benefits over existing PAH therapies.

About Pulmonary Arterial Hypertension

PAH is a highly debilitating disease characterized by severe constriction of the blood vessels in the lungs leading to very high pulmonary arterial pressures. These high pressures make it difficult for the heart to pump blood through the lungs to be oxygenated. Patients with PAH suffer from extreme shortness of breath as the heart struggles to pump against these high pressures causing such patients to ultimately die of heart failure. PAH can occur with no known underlying cause, or it can occur secondary to diseases like scleroderma (an autoimmune disease of the connective tissues), cirrhosis of the liver, congenital heart defects and HIV infection. PAH afflicts approximately 200,000 patients worldwide.

About Ambrisentan

Ambrisentan is being developed as an oral therapy for patients with PAH and has been granted orphan drug designation for the treatment of PAH in both the United States and European Union.

Ambrisentan is a type-A selective propanoic acid-class endothelin receptor antagonist, which acts as a potent inhibitor of endothelin-induced proliferation and 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.

About Myogen

Myogen is a biopharmaceutical company focused on the discovery, development and commercialization of small molecule therapeutics for the treatment of cardiovascular disorders. Myogen currently markets one product in Europe for the treatment of acute decompensated heart failure and has two product candidates in late-stage clinical development: ambrisentan for the treatment of patients with pulmonary arterial hypertension and darusentan for the treatment of patients with resistant hypertension. The Company, in collaboration with Novartis, also conducts a target and drug discovery research program focused on the development of disease-modifying drugs for the treatment of chronic heart failure and related cardiovascular disorders. Please visit Myogen's website at www.myogen.com.

Safe Harbor Statement

This press release contains forward-looking statements that involve significant risks and uncertainties, including statements relating to ambrisentan clinical data and the completion and release of results of the Company's ARIES clinical trials. Actual results could differ materially from those projected and the Company cautions investors not to place undue reliance on the forward-looking statements contained in this release.

Among other things, the projected completion of the Company's clinical trials, including the ARIES trials, and the timing of the release of results of clinical trials may be affected by difficulties or delays, including difficulties or delays in patient treatment, data collection and data analysis. Delays in clinical trials, whether caused by competition, adverse events, patient enrollment rates, regulatory issues or other factors, could adversely affect the Company's financial position and prospects. The results of Myogen's prior clinical trials of its product candidates, including ambrisentan, do not necessarily predict the results of later-stage clinical trials, including the results of the Company's ARIES-1 and ARIES-2 clinical trials. Top line results of a clinical trial may not be confirmed upon full analysis of the detailed results of the trial. If the Company's product candidates, including ambrisentan, do not meet safety or efficacy endpoints in clinical evaluations, they will not receive regulatory approval and the Company will not be able to market them. Even if the Company's product candidates meet safety and efficacy endpoints, regulatory authorities may not approve them, or the Company may face post-approval problems that require the withdrawal of its product from the market. There can be no assurance that Myogen's product candidates, including ambrisentan, have better efficacy or safety profiles than competing products, including a lower incidence of liver toxicity or liver toxicity that is not dose dependent. Myogen's results may also be affected by competition from other pharmaceutical and biotechnology companies, Myogen's ability to successfully develop and market its current products, regulatory developments involving current and future products and its effectiveness at managing its financial resources. If the Company is unable to raise additional capital when required or on acceptable terms, it may have to significantly delay, scale back or discontinue one or more of its drug development or discovery research programs. Myogen is at an early stage of development and may not ever have any products that generate significant revenue.

Additional risks and uncertainties relating to the Company and its business can be found in the "Risk Factors" section of Myogen's Form 10-K for the year ended December 31, 2004 and Myogen's reports on Form 10-Q and Form 8-K. It is Myogen's policy to only update or reconfirm its public guidance by issuing a press release or filing a periodic or current report with the Securities and Exchange Commission. The Company generally plans to provide guidance as part of its annual and quarterly earnings releases but reserves the right to provide guidance at different intervals or to revise its practice in future periods. All information in this press release is as of November 10, 2005. Myogen undertakes no duty or obligation to update any forward-looking statements contained in this release as a result of new information, future events or changes in the Company's expectations. The Company also disclaims any duty to comment upon or correct information that may be contained in reports published by the investment community.

Myogen, Inc.

CONTACT: Derek K. Cole, Director, Investor Relations of Myogen, Inc.,+1-303-464-3986, derek.cole@myogen.com

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