MIRROR Open-Label Study Topline Data of Methotrexate with KRYSTEXXA (pegloticase injection) Indicates Significant Improvement in Response Rate

-- Seventy-Nine Percent of Patients Achieved a Complete Response --

-- New Data Continues to Support Immunomodulation Strategy to Improve Patient Outcomes --

DUBLIN, Ireland I January 13, 2020 I Horizon Therapeutics plc (Nasdaq: HZNP) announced today topline results from its MIRROR open-label study in which methotrexate with KRYSTEXXA® (pegloticase injection) provided an increased durability of response for people living with chronic gout refractory to conventional therapies – also known as uncontrolled gout.

Data from the Methotrexate to Increase Response Rates in Patients With Uncontrolled GOut Receiving KRYSTEXXA (MIRROR OL) shows that 79 percent, or 11 of 14 patients, achieved a complete response, defined as the proportion of serum uric acid (sUA) responders (sUA < 6 mg/dL) at Month 6. Detailed results from the study will be presented at a future medical meeting. The co-prescription of KRYSTEXXA and methotrexate is investigational and its safety and efficacy have not been established.

KRYSTEXXA has demonstrated rapid reduction in sUA levels for people with uncontrolled gout; however, treatment with biologic medicines can, in some, trigger the body’s immune system to develop anti-drug antibodies. These anti-drug antibodies can reduce the effectiveness of the biologic therapy. Immunomodulators such as methotrexate, which is commonly used by rheumatologists, can help reduce this reaction.

The MIRROR open-label pilot study follows other studies that showed an improved response rate when KRYSTEXXA is co-administered with methotrexate. This includes an independent case series presented at the Annual European Congress of Rheumatology meeting in June 2019 in which the administration of KRYSTEXXA with methotrexate resulted in a 100 percent response (10 of 10 patients) as defined by greater than 80 percent of sUA levels being maintained at goal (<6.0 mg/dL) during the treatment period.1 Further, a separate case series presented at the American College of Rheumatology meeting in November 2019 resulted in an 80 percent response (8 of 10 patients) as defined by receiving ≥12 infusions without loss of sUA response.2

“There is a growing body of data supporting the potential of KRYSTEXXA plus methotrexate rather than KRYSTEXXA therapy alone,” said Paul Peloso, M.D., M.Sc., vice president and therapeutic area head, rheumatology, Horizon. “We continuously evaluate our therapies to ensure every patient can achieve the best possible outcomes. With a 79 percent response rate in combination with methotrexate, which is significantly higher than the 42 percent response rate in the KRYSTEXXA Phase 3 clinical program that evaluated KRYSTEXXA alone, more people living with uncontrolled gout may be able to benefit from a full course of therapy.”

Horizon is currently conducting a separate, placebo-controlled MIRROR trial (NCT03994731) evaluating the use of KRYSTEXXA and methotrexate. The trial, with 135 randomized patients, is designed to enable the potential for submission of results to the U.S. Food and Drug Administration (FDA) for update to the label.

In addition, Horizon is planning to evaluate the impact of administering KRYSTEXXA over a shorter infusion duration. The initial proof-of-concept work will begin mid-2020. Currently, KRYSTEXXA is infused over a two-hour or longer timeframe. A shorter infusion duration could meaningfully improve the experience and convenience for patients, physicians and sites of care.


KRYSTEXXA® (pegloticase injection) is a PEGylated uric acid specific enzyme indicated for the treatment of chronic gout in adult patients refractory to conventional therapy.

Gout refractory to conventional therapy occurs in patients who have failed to normalize serum uric acid and whose signs and symptoms are inadequately controlled with xanthine oxidase inhibitors at the maximum medically appropriate dose or for whom these drugs are contraindicated.

About Horizon

Horizon is focused on researching, developing and commercializing medicines that address critical needs for people impacted by rare and rheumatic 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, follow us @HorizonNews on Twitter, like us on Facebook or explore career opportunities on LinkedIn.


  1. Pretreatment and co-administration with methotrexate improved durability of pegloticase response: a prospective, observational, proof-of-concept, case series. Poster presented at the 2019 Annual European Congress of Rheumatology (EULAR), Madrid, Spain; June 12-15, 2019
  2. Subcutaneous or oral methotrexate exposure and response to pegloticase in uncontrolled gout patients in a community rheumatology practice. Poster presented at the 2019 Annual Scientific Meeting of the American College of Rheumatology (ACR/ARP), Atlanta, GA, USA; November 8 – 13, 2019.

SOURCE: Horizon

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