Horizon Pharma plc Completes Target Enrollment of 90 Patients for Phase 3 Trial of ACTIMMUNE(R) (interferon gamma-1b) for the Treatment of People With Friedreich’s Ataxia

DUBLIN, IRELAND–(Marketwired – May 5, 2016) – Horizon Pharma plc (NASDAQ: HZNP), a biopharmaceutical company focused on improving patients’ lives by identifying, developing, acquiring and commercializing differentiated and accessible medicines that address unmet medical needs, today announced that it has completed target enrollment of its Phase 3 study evaluating ACTIMMUNE (interferon gamma-1b) for the treatment of people with Friedreich’s ataxia (FA), a degenerative neuro-muscular disorder. The study (NCT02415127) has reached its target enrollment of 90 patients at four sites in the United States, and top-line results are expected by the end of 2016.

“The achievement of this important milestone would not have been possible without the passionate commitment of people living with FA, the Friedreich’s Ataxia Research Alliance and our Phase 3 study investigators,” said Jeffrey W. Sherman, M.D., FACP, executive vice president, research and development and chief medical officer, Horizon Pharma plc. “We are grateful for their collective partnership and guidance, which drives our efforts toward providing a potential treatment option for this debilitating disorder.”

The Safety, Tolerability and Efficacy of ACTIMMUNE Dose Escalation in Friedreich’s Ataxia study (“STEADFAST“) is a randomized, multi-center, double-blind, placebo-controlled study with patients randomized 1:1 to receive subcutaneous doses of either ACTIMMUNE or placebo three times a week for a total of 26 weeks. The primary endpoint will evaluate the effect of ACTIMMUNE versus placebo on the change from baseline to Week 26 in neurological outcome as measured by a modified version of the Friedreich’s Ataxia Rating Scale (FARS). The FARS is used to measure neurological signs associated with FA, with higher scores reflecting a greater level of disability. In addition to safety and efficacy, the STEADFAST trial will evaluate the pharmacokinetic characteristics of ACTIMMUNE in people with FA. After completion of the study, patients who participated in STEADFAST will have the opportunity to transition to an open-label extension study (NCT02593773).

“The prompt recruitment and enrollment of this study reflects the urgent unmet need as well as the commitment to participate in research among people living with FA,” said Ronald J. Bartek, co-founder and founding president, Friedreich’s Ataxia Research Alliance (FARA). “As an organization dedicated to the pursuit of scientific research leading to treatments for FA, we are very pleased with the progress of the STEADFAST study and are hopeful that the results lead to the first approved treatment for people living with FA.”

In April 2015, ACTIMMUNE was granted Fast Track status for FA by the U.S. Food and Drug Administration (FDA). This designation provides greater access to and more frequent communication with the FDA throughout the entire drug development and review process, with the goal of possibly expediting approval. Fast Track designation also gives Horizon Pharma the opportunity to potentially submit sections of the ACTIMMUNE registration dossier for FA on a rolling basis, and allows ACTIMMUNE to be considered for priority review at the time of submission based on forthcoming clinical data.

About Friedreich’s ataxia (FA)
FA is a debilitating, life-shortening and degenerative neuro-muscular disorder that affects approximately 4,000 people in the United States. Onset of symptoms can vary from five years old to adulthood, with the childhood onset tending to be associated with a more rapid progression. A progressive loss of coordination and muscle strength leads to motor incapacitation and often the full-time use of a wheelchair. Most young people diagnosed with FA require mobility aids such as a cane, walker or wheelchair by their teens or early 20’s. There are currently no approved treatments for FA.

About ACTIMMUNE
ACTIMMUNE (interferon gamma-1b) is a biologically manufactured protein similar to one the body makes naturally to help prevent infection. ACTIMMUNE is currently approved by the U.S. Food and Drug Administration (FDA) for use in two rare diseases. It is indicated to reduce the frequency and severity of serious infections associated with Chronic Granulomatous Disease (CGD), a genetic disorder that affects the functioning of some cells of the immune system. In addition, ACTIMMUNE is indicated to slow the worsening of severe, malignant osteopetrosis (SMO), a genetic disorder that affects normal bone formation. For more information, please see www.ACTIMMUNE.com.

ACTIMMUNE is not indicated for FA.

ACTIMMUNE Important Safety Information
ACTIMMUNE is contraindicated in patients who develop or have known hypersensitivity to interferon-gamma, E coli-derived products, or any component of the product

ACTIMMUNE should be used with caution in patients with:

• pre-existing cardiac conditions, including ischemia, congestive heart failure, or arrhythmia
• Seizure disorders or compromised central nervous system function; reduce dose or discontinue
• Myelosuppression, or receiving other potentially myelosuppressive agents; consider dose reduction or discontinuation of therapy
• Severe renal insufficiency
• Age < 1 year

Monitoring:

• Patients begun on ACTIMMUNE before age 1 year should receive monthly assessments of liver function. If severe hepatic enzyme elevations develop, ACTIMMUNE dosage should be modified
• Monitor renal function regularly when administering ACTIMMUNE in patients with severe renal insufficiency; accumulation of interferon gamma-1b may occur with repeated administration. Renal toxicity has been reported in patients receiving ACTIMMUNE

Pregnancy, Lactation, and Fertility:

• ACTIMMUNE should be used during pregnancy only if the potential benefit outweighs the potential risk to the fetus
• Use of ACTIMMUNE by lactating mothers is not recommended. ACTIMMUNE or nursing should be discontinued dependent on the importance of the drug to the mother
• Long-term effects of ACTIMMUNE on fertility are not known

Drug Interactions:

• Concomitant use of drugs with neurotoxic, hematotoxic or cardiotoxic effects may increase the toxicity of interferons
• Avoid simultaneous administration of ACTIMMUNE with other heterologous serum protein or immunological preparations (e.g., vaccines)

Adverse Reactions:

• The most common adverse experiences occurring with ACTIMMUNE therapy are “flu-like” symptoms such as fever, headache, chills, myalgia, or fatigue, which may decrease in severity as treatment continues, and may be minimized by bedtime administration of ACTIMMUNE
• Acetaminophen may be used to prevent or partially alleviate the fever and headache
• Isolated cases of acute serious hypersensitivity reactions have been observed in patients receiving ACTIMMUNE
• Reversible neutropenia, thrombocytopenia, and elevations of AST and/or ALT have been observed during ACTIMMUNE therapy
• At doses 10 times greater than the weekly recommended dose, ACTIMMUNE may exacerbate pre-existing cardiac conditions, or may cause reversible neurological effects such as decreased mental status, gait disturbance, and dizziness

Visit www.ACTIMMUNE.com to download a copy of the ACTIMMUNE Full Prescribing Information.

About Horizon Pharma plc
Horizon Pharma plc is a biopharmaceutical company focused on improving patients’ lives by identifying, developing, acquiring and commercializing differentiated and accessible medicines that address unmet medical needs. The Company markets nine medicines through its orphan, rheumatology and primary care business units. Horizon’s global headquarters are in Dublin, Ireland. For more information, please visit www.horizonpharma.com. Follow @HZNPplc on Twitter or view careers on our LinkedIn page.

Forward Looking Statements
This press release contains forward-looking statements, including statements regarding the timing of results of the Phase 3 trial of ACTIMMUNE in Friedreich’s ataxia, the potential benefits of Fast Track designation, and the potential for ACTIMMUNE as a treatment for Friedreich’s ataxia. Forward-looking statements speak only as of the date of this press release and Horizon does not undertake any obligation to update or revise these statements, except as may be required by law. These forward-looking statements are based on management’s expectations and assumptions as of the date of this press release and actual results may differ materially from those in these forward-looking statements as a result of various factors. These factors include, but are not limited to, risks regarding whether results of subsequent studies will be consistent with results of prior studies, whether Horizon experiences delays in completing the Phase 3 trial, whether the results of the Phase 3 trials will be sufficient to support marketing approval of ACTIMMUNE as a treatment for Friedreich’s ataxia, whether Horizon will conduct further studies of ACTIMMUNE or have the financial resources to do so, whether Horizon realizes any of the potential benefits of Fast Track designation, and the risks associated with pre-clinical and clinical development of drug candidates. For a further description of these and other risks facing Horizon, please see the risk factors described in Horizon’s filings with the United States Securities and Exchange Commission, including those factors discussed under the caption “Risk Factors” in those filings. Forward-looking statements speak only as of the date of this press release and Horizon undertakes no obligation to update or revise these statements, except as may be required by law.