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Horizon Pharma plc Completes Enrollment of Confirmatory Phase 3 Trial of Teprotumumab Ahead of Schedule

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--Topline results expected in second quarter of 2019 --

Horizon Pharma plc (NASDAQ:HZNP) announced the early completion of
enrollment for the confirmatory Phase 3 trial of teprotumumab in
patients living with moderate-to-severe active thyroid eye disease
(TED). The study (NCT03298867
and EudraCT
2017-002763-18
) enrolled 83 patients at 13 sites across the United
States, Germany and Italy. Topline results are expected in the second
quarter of 2019.

"Our success in rapidly enrolling this trial speaks to the significant
unmet need and the strong collaboration with Phase 3 study
investigators," said Timothy P. Walbert, chairman, president and chief
executive officer, Horizon Pharma plc. "There is no FDA-approved therapy
for TED, which can result in bulging of the eyes, known as proptosis,
and cause additional challenges for those living with the disease.
Completing enrollment in our confirmatory Phase 3 trial marks a key
milestone for people living with TED and Horizon Pharma. We look forward
to the Phase 3 data analysis and the potential opportunity to bring this
therapy to TED patients."

The Treatment of Graves' Orbitopathy (Thyroid Eye Disease) to
Reduce Proptosis with Teprotumumab Infusions in a
Randomized, Placebo-Controlled, Clinical Study (OPTIC)
is a
randomized, double-masked, placebo-controlled, parallel-group,
multicenter study. OPTIC reached its target enrollment of 76 patients on
Aug. 3, those remaining in screening were allowed to randomize for a
final total of 83 patients. Patients will be randomized in a 1:1 ratio
to receive eight infusions of teprotumumab or placebo every three weeks
for 21 weeks. The primary endpoint is the responder rate of ≥ 2 mm
reduction of proptosis, or bulging of the eye, in the study eye (without
deterioration in the fellow eye) at week 24, in teprotumumab treated
versus placebo treated patients. In addition, the secondary endpoints at
week 24, include overall responder rate, percentage of participants with
a Clinical Activity Score value of 0 or 1, mean change from baseline in
proptosis measurement and the Graves' Ophthalmopathy Quality of Life
questionnaire overall score. Safety is evaluated throughout the duration
of the study. Teprotumumab is an investigational medicine and its safety
and efficacy have not been established.

About Thyroid Eye Disease

Thyroid eye disease (TED) is a rare autoimmune disease in which the
insulin-like growth factor receptor (IGF-1R) is overexpressed on eye
tissues, resulting in local inflammation, orbital fibroblast
proliferation and tissue expansion, which can in turn lead to proptosis,
or bulging of the eye. In some cases the swelling and stiffness of the
muscles due to fibroblast proliferation and inflammation displace the
eyes so that they are no longer in line with each other, or the eyelids
are unable to close. The inability for people living with TED to close
their eyelids can lead to corneal ulcerations and potential blindness,
and many also endure challenges with double vision, known as diplopia.

About Teprotumumab

Teprotumumab is a fully human monoclonal antibody (mAb) and a targeted
inhibitor of the insulin-like growth factor 1 receptor (IGF-1R).
Teprotumumab has received Breakthrough Therapy, Orphan Drug and Fast
Track designations from the U.S. Food and Drug Administration (FDA). The
Phase 3 confirmatory study was launched in October 2017 after results
from the randomized double-blind, placebo controlled Phase 2 study.
Results from this study were published
in the May 4, 2017, issue of The New England Journal of Medicine.

The Phase 2 study was designed to evaluate the efficacy and safety of
teprotumumab in patients with recent onset, moderate-to-severe active
TED. The primary endpoint was response in the study eye defined as a
reduction in Clinical Activity Score of ≥ 2 points and reduction of
proptosis of ≥ 2 mm at week 24. In the intent-to-treat population, 29 of
42 (69%) patients receiving teprotumumab and 9 of 45 (20%) patients
receiving placebo were responders at week 24 (p˂0.001). The most
frequent adverse events reported (≥ 5 percent) were nausea, muscle
spams, diarrhea, alopecia, hyperglycemia, dry skin, headache,
paresthesia, hearing impairment and weight loss. Teprotumumab is an
investigational medicine and its safety and efficacy have not been
established.

Forward-Looking Statements

This press release contains forward-looking statements, including
statements regarding the timing of results from the Phase 3 trial of
teprotumumab in the treatment of TED and the potential for teprotumumab
as a treatment for TED. Forward-looking statements speak only as of the
date of this press release and Horizon Pharma 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 the
Phase 3 trial will be consistent with results of prior trials, whether
Horizon experiences delays in completing the Phase 3 trial, whether the
results of the Phase 3 trial will be sufficient to support marketing
approval of teprotumumab as a treatment for TED, and the risks
associated with clinical development of drug candidates. For a further
description of these and other risks facing Horizon, please see the risk
factors described in Horizon Pharma'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
Pharma undertakes no obligation to update or revise these statements,
except as may be required by law.

About Horizon Pharma plc

Horizon Pharma plc is focused on researching, developing and
commercializing innovative medicines that address unmet treatment needs
for rare and rheumatic diseases. By fostering a growing pipeline of
medicines in development and exploring all potential uses for currently
marketed medicines, we strive to make a powerful difference for
patients, their caregivers and physicians. For us, it's personal: by
living up to our own potential, we are helping others live up to theirs.
For more information, please visit www.horizonpharma.com.
Follow @HZNPplc on
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