Dyax Presents Integrated Analysis of Phase 3 Data for DX-88 for Hereditary Angioedema

Dyax Corp. (Nasdaq:DYAX) announced presentation of an integrated analysis of the two DX-88 Phase 3 studies demonstrating that treatment with DX-88 (ecallantide) provided clinically meaningful, rapid and sustained relief of symptoms in acute attacks of hereditary angioedema (HAE), when compared to placebo. This analysis, which included 143 unique patients treated with DX-88 or placebo, reinforces the robust efficacy findings seen for DX-88 in both its Phase 3 studies.

Statistically significant improvement in symptoms was demonstrated with DX-88 at four hours after treatment and persisted throughout the 24-hour period of evaluation. The integrated analysis also demonstrated that DX-88 was efficacious in treating all acute attack locations (laryngeal, abdominal, peripheral) and was well tolerated, with no treatment-related serious adverse events. These findings were derived from an integrated analysis of the double-blind portion of the Company’s first Phase 3 trial, known as EDEMA3, and its second Phase 3 trial, known as EDEMA4, and were presented for the first time at the 6^th Annual International C1-INH Deficiency Workshop on May 24, 2009 in Budapest, Hungary¹ and subsequently on June 7, 2009, at the XXVIII European Asthma, Allergy and Clinical Immunology (EAACI) Congress in Warsaw, Poland.²

"The integrated analysis further underscores the efficacy and safety of DX-88 previously seen in the clinical trial experience,” stated Dr. Henry Li of the Institute for Asthma & Allergy in Wheaton, MD and EDEMA3 and EDEMA4 clinical trial investigator. "HAE patients live with a daily fear of the potential onset of a life-threatening laryngeal acute attack. With its demonstrated rapid relief of acute symptoms and durability of response, DX-88 offers hope for HAE patients to regain control of their everyday lives.”

Additionally, new data from EDEMA4 presented in a poster discussion led by Dr. Robyn Levy, allergist and immunologist at the Family Allergy & Asthma Center in Atlanta, GA and EDEMA4 principal investigator, suggested that DX-88 is able to stop progression of acute attacks of HAE. The data showed that fewer patients experienced emerging HAE symptoms after treatment with DX-88 (n=2) than did placebo-treated patients (n=7). Of the placebo-treated patients with emerging symptoms, three experienced emerging laryngeal symptoms, which can be fatal if untreated.³

"Preventing the emergence of additional HAE symptoms during an acute attack is of enormous significance to HAE patients, particularly in relation to a progression of a life-threatening laryngeal attack,” said Dr. Robyn Levy.

Highlights from the Integrated Analysis: ^1,2

The integrated analysis includes data from the first treatment episode for each patient in the Phase 3 trials. In the combined studies, 143 unique patients were treated with DX-88 or placebo.

Key findings include the following:

• DX-88 demonstrated statistically significant improvements in the severity of an HAE attack compared to placebo. From baseline to 4 hours, median severity in Mean Symptom Complex Severity (MSCS) scores decreased significantly with DX-88 (-1.0) versus placebo (-0.3; p<0.001). Median Treatment Outcome Score (TOS) at 4 hours was significantly higher with DX-88 (50.0) versus placebo (0.0; p<0.001).
• Durability of response was demonstrated by a statistically significant decrease in MSCS score at 24 hours for the DX-88 group versus placebo (p=0.028) and a significantly higher TOS at 24 hours (p=0.041).
• Rapid relief with DX-88 was indicated by statistically significant improvement in TOS within 2 hours after dosing (p=0.012).
• DX-88 demonstrated significantly better response than placebo for all HAE attack locations. Mean TOS 4 hours after dosing was significantly higher for abdominal (p=0.026), laryngeal (p=0.041) and peripheral (p=0.035) attacks.
• DX-88 was well tolerated, with no reported treatment-related serious AEs. Treatment-related adverse events (AEs) were similar for each patient group: DX-88 (15%) and placebo (14%). The majority of AEs reported were mild or moderate.

Summary of Phase 3 Evaluation (EDEMA3 and EDEMA4)

EDEMA3, a 72-patient, placebo-controlled, multi-center, Phase 3 trial was conducted in the United States, Europe, Canada and Israel. The trial had two phases: a double-blind, placebo-controlled phase and a repeat dosing phase. EDEMA4, a 96-patient, double-blind, placebo-controlled, multi-center, Phase 3 trial, was conducted in the United States and Canada.

The primary objective of EDEMA3 and EDEMA4 was to determine the efficacy and safety of the fixed 30 mg subcutaneous dose of DX-88 for patients suffering from moderate to severe acute HAE attacks. Two HAE-specific patient reported outcome (PRO) measures were developed to assess efficacy endpoints in the EDEMA3 and EDEMA4 trials. The Mean Symptom Complex Severity (MSCS) score is a point-in-time assessment of individual symptom burden that accounts for symptom location and severity of the attack using a score from 0 to 3 (0=normal, 3=severe). The Treatment Outcome Score (TOS) is a composite measure of treatment response based on a scale of 100 to -100 (100=significant improvement, -100 significant worsening) and taking into account symptom severity at baseline.

The following abstracts from studies supported by Dyax were presented:

International C1-INH Deficiency Workshop Data Presentation

1 Integrated analysis of two phase 3, double-blind, placebo-controlled studies of DX-88 (ecallantide) for the treatment of hereditary angioedema – Oral presentation, H. Henry Li, MD, PhD, FAAAAI, Institute for Asthma & Allergy in Wheaton, MD – Sunday, May 24, 2009

EAACI Data Presentations

2 Subcutaneous DX-88 (ecallantide) for the treatment of acute attacks of hereditary angioedema: results from the integrated analysis of phase 3, double-blind, placebo-controlled studies – Oral presentation, Patrick T. Horn, MD, PhD, Dyax Corp. – Sunday, June 7, 2009

3 Subcutaneous DX-88 (ecallantide) for the treatment of acute attacks of hereditary angioedema: results from the pivotal phase 3, double-blind, placebo-controlled EDEMA4 trial – Poster discussion, Robyn J. Levy, MD, Family Allergy & Asthma Center in Atlanta, GA – Sunday, June 7, 2009

About DX-88 for HAE

The recombinant, small protein, DX-88 (ecallantide), was discovered utilizing Dyax’s proprietary phage display technology and is being evaluated as a subcutaneous therapy for treating acute HAE attacks. DX-88 is a potent and selective plasma kallikrein inhibitor, a key mediator of inflammation in angioedema, and has demonstrated effectiveness for treating all attack locations, including life-threatening laryngeal attacks. DX-88 has been evaluated in five clinical trials for HAE, including two Phase 3 placebo-controlled trials, which represent the largest placebo-controlled evaluation for this indication. A continuation trial is ongoing.

About HAE

Hereditary angioedema (HAE) is an acute inflammatory condition characterized by episodes of severe, often painful swelling affecting the extremities, the gastrointestinal tract, the genitalia, and in potentially life-threatening cases, the larynx. HAE is caused by low or dysfunctional levels of C1 esterase inhibitor (C1-INH), a naturally occurring molecule that inhibits plasma kallikrein and other serine proteases in the blood.

About Dyax

Dyax is focused on advancing novel biotherapeutics for unmet medical needs, with an emphasis on inflammatory and oncology indications. Dyax utilizes its proprietary drug discovery technology to identify antibody, small protein and peptide compounds for clinical development. Dyax’s lead product candidate is DX-88 (ecallantide), a recombinant small protein that is currently being evaluated for its therapeutic potential in two separate indications. On June 1, 2009, Dyax submitted a response to the FDA’s Complete Response letter regarding the review of Dyax’s Biologics License Application (BLA) of DX-88 for the treatment of hereditary angioedema (HAE). The FDA accepted the submission and assigned Dyax’s BLA a new Prescription Drug User Fee Act (PDUFA) action date of December 1, 2009. DX-88 has orphan drug designation in the U.S. and E.U., as well as Fast Track designation in the U.S., for this indication. Additionally, DX-88 is being evaluated in Phase 2 trials for the prevention of blood loss during on-pump cardiothoracic surgery (CTS), which are being conducted by Dyax’s partner, Cubist Pharmaceuticals. Dyax licensed to Cubist the intravenous formulation of DX-88 for surgical indications in North America and Europe. DX-88 and other compounds in Dyax’s pipeline were identified using its patented phage display technology, which rapidly selects compounds that bind with high affinity and specificity to therapeutic targets. Dyax leverages this technology broadly with over 70 revenue generating licenses and collaborations for therapeutic discovery, as well as in non-core areas such as affinity separations, diagnostic imaging, and research reagents. Dyax is headquartered in Cambridge, Massachusetts. For online information about Dyax Corp., please visit www.dyax.com.

Dyax Disclaimer

This press release contains forward-looking statements, including statements regarding the prospects for therapeutic benefits and treatment advantages of DX-88 for HAE. Statements that are not historical facts are based on Dyax’s current expectations, beliefs, assumptions, estimates, forecasts and projections about the industry and markets in which Dyax competes. The statements contained in this release are not guarantees of future performance and involve certain risks, uncertainties and assumptions, which are difficult to predict. Therefore, actual outcomes and results may differ materially from what is expressed in such forward-looking statements. Important factors which may affect the prospects for therapeutic benefits and treatment advantages of DX-88 for HAE and include the risks that: DX-88 could take a significantly longer time to gain regulatory approval than Dyax expects or may never gain approval; others may develop technologies or products superior to DX-88 or that are on the market before DX-88; DX-88 may not gain market acceptance; Dyax is dependent on the expertise, effort, priorities and contractual obligations of third parties in the manufacture, marketing, sales and distribution of DX-88; and other risk factors described or referred to Item 1A, "Risk Factors” in Dyax’s most recent Annual Report on Form 10-K and other periodic reports filed with the Securities and Exchange Commission. Dyax cautions investors not to place undue reliance on the forward-looking statements contained in this release. These statements speak only as of the date of this release, and Dyax undertakes no obligations to update or revise these statements, except as may be required by law.

Dyax and the Dyax logo are registered trademarks of Dyax Corp. EDEMA3 and EDEMA4 are registered service marks of Dyax.