-- Comprehensive OPTIC-X trial results published in Ophthalmology, including new long-term follow-up data --

Horizon Therapeutics plc (Nasdaq: HZNP) today announced additional data supporting the long-term efficacy of TEPEZZA for the treatment of TED. Data were published in Ophthalmology. TEPEZZA is the first and only medicine approved by the U.S. Food and Drug Administration (FDA) for the treatment of TED – a serious, progressive and potentially vision-threatening rare autoimmune disease.¹

Comprehensive results from the OPTIC-X open-label extension clinical trial were published in Ophthalmology – including new long-term data for people with longer disease duration. As previously reported, 89% (33/37) of patients who received placebo in OPTIC and went on to receive TEPEZZA in OPTIC-X became proptosis responders (average reduction of -3.5 mm). These patients had median duration of TED for 12.9 months versus 6.3 months in those treated with TEPEZZA in OPTIC. New data in this publication show a high rate of maintained response at Week 48 (27 weeks after last dose): 90.6% for proptosis (29/32); 91.7% for overall response (22/24); 95.2% for a Clinical Activity Score (CAS) of 0 or 1 (20/21); and 85.7% for diplopia (12/14). There were no new safety concerns in either OPTIC-X or the OPTIC off-treatment follow-up period, including patients who received additional TEPEZZA treatment in OPTIC-X.

“Given the rare nature of Thyroid Eye Disease, it can take several months or years to get diagnosed – making it particularly encouraging to see that even those who have had the disease for a longer period of time can still have a sustained response to TEPEZZA,” said Jeffrey W. Sherman, M.D., FACP, executive vice president, chief medical officer, Horizon. “Thyroid Eye Disease can take a significant toll on people who are living with the disease, affecting them both physically and emotionally. Through ongoing research, we will continue to deepen our understanding of the longevity of response to TEPEZZA, which is important to both people with TED and physicians.”

Longer-term follow-up results from the OPTIC Phase 3 clinical trial were also shared at the 90^th Annual Meeting of the American Thyroid Association (ATA) earlier this month. Of the OPTIC patients who received TEPEZZA and completed the 48-week follow-up, 90% (18/20) received no additional therapy as of Week 120. One patient received TEPEZZA 16 months after the last dose and one had eyelid surgery a year after the last dose. OPTIC non-responders (TEPEZZA n=5; placebo n=36) or those who flared (TEPEZZA n=9; placebo n=1) during the OPTIC follow-up period were treated for the first time or retreated with TEPEZZA in the OPTIC-X open-label extension clinical trial.

“Findings from this extended follow-up period reinforce previously-reported data showing that the majority of people treated with TEPEZZA have a sustained response,” said Terry J. Smith, M.D., Michigan Medicine Eye Plastic, Facial Cosmetic & Orbital Surgery, Kellogg Eye Center, University of Michigan Medical School, and senior study author. “This is the longest period of follow-up data we have for TEPEZZA and it can play an important role in helping physicians determine when in the disease course to optimally prescribe the medicine for their patients.”

About Thyroid Eye Disease (TED)

TED is a serious, progressive and potentially vision-threatening rare autoimmune disease.¹ TED often occurs in people living with Graves’ disease, but is a distinct disease that is caused by autoantibodies activating an IGF-1R-mediated signaling complex on cells within the retro-orbital space.^2,3 This leads to a cascade of negative effects, which may cause long-term, irreversible damage. As TED progresses, the serious damage it can cause includes proptosis (eye bulging), strabismus (misalignment of the eyes) and diplopia (double vision) – and in some cases can lead to blindness.^4,5

About TEPEZZA

INDICATION

TEPEZZA is indicated for the treatment of Thyroid Eye Disease.

IMPORTANT SAFETY INFORMATION

Warnings and Precautions

Infusion Reactions: TEPEZZA may cause infusion reactions. Infusion reactions have been reported in approximately 4% of patients treated with TEPEZZA. Reported infusion reactions have usually been mild or moderate in severity. Signs and symptoms may include transient increases in blood pressure, feeling hot, tachycardia, dyspnea, headache and muscular pain. Infusion reactions may occur during an infusion or within 1.5 hours after an infusion. In patients who experience an infusion reaction, consideration should be given to premedicating with an antihistamine, antipyretic, or corticosteroid and/or administering all subsequent infusions at a slower infusion rate.

Preexisting Inflammatory Bowel Disease: TEPEZZA may cause an exacerbation of preexisting inflammatory bowel disease (IBD). Monitor patients with IBD for flare of disease. If IBD exacerbation is suspected, consider discontinuation of TEPEZZA.

Hyperglycemia: Increased blood glucose or hyperglycemia may occur in patients treated with TEPEZZA. In clinical trials, 10% of patients (two-thirds of whom had preexisting diabetes or impaired glucose tolerance) experienced hyperglycemia. Hyperglycemic events should be managed with medications for glycemic control, if necessary. Monitor patients for elevated blood glucose and symptoms of hyperglycemia while on treatment with TEPEZZA. Patients with preexisting diabetes should be under appropriate glycemic control before receiving TEPEZZA.

Adverse Reactions

The most common adverse reactions (incidence ≥5% and greater than placebo) are muscle spasm, nausea, alopecia, diarrhea, fatigue, hyperglycemia, hearing impairment, dysgeusia, headache and dry skin.

For additional information on TEPEZZA, please see Full Prescribing Information at TEPEZZAhcp.com.

About Horizon

Horizon is focused on the discovery, development and commercialization of medicines that address critical needs for people impacted by rare, autoimmune and severe inflammatory diseases. Our pipeline is purposeful: we apply scientific expertise and courage to bring clinically meaningful therapies to patients. We believe science and compassion must work together to transform lives. For more information on how we go to incredible lengths to impact lives, please visit www.horizontherapeutics.com and follow us on Twitter, LinkedIn, Instagram and Facebook.

Forward-Looking Statements

This press release contains forward-looking statements, including statements regarding the potential benefits of TEPEZZA, the utility of new data from the OPTIC and OPTIC-X clinical trials and Horizon’s plans to continue studying the longevity of TEPEZZA responses. 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 future data analyses or clinical evidence will be consistent with prior data and the extent to which physicians prescribe TEPEZZA to certain TED patients. 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.

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