MIRROR Randomized Controlled Trial Meets Primary Endpoint and Shows 71% of Patients Achieved a Complete Response Rate Using KRYSTEXXA (pegloticase injection) with Methotrexate

Horizon Therapeutics plc (Nasdaq: HZNP) today announced topline results met the primary endpoint, showing a significant increase in efficacy using KRYSTEXXA with the immunomodulator methotrexate as compared to the response rate of KRYSTEXXA with placebo for people with chronic gout refractory to conventional therapies – also known as uncontrolled gout. Results were from the Methotrexate to Increase Response Rates in Patients with Uncontrolled Gout Receiving KRYSTEXXA trial [MIRROR randomized controlled trial (RCT)].

“It is rare that you can improve a response rate so substantially for patients; by 30 percentage points in this case based on the results of our trial,” said Elizabeth H.Z. Thompson, Ph.D., executive vice president, research and development, Horizon. “These results reinforce what we have seen from published case series as well as our open-label trial evaluating KRYSTEXXA with methotrexate. Horizon has invested significantly over the last several years to ensure more uncontrolled gout patients are able to benefit from KRYSTEXXA and we continue to develop new approaches that target the underlying cause of gout.”

In the MIRROR randomized controlled trial, 152 adults living with uncontrolled gout were randomized to receive methotrexate or placebo for four weeks and then treatment with KRYSTEXXA and methotrexate or KRYSTEXXA and placebo for 52 weeks. This trial was designed to evaluate the concomitant use of KRYSTEXXA with methotrexate, an immunomodulator commonly prescribed by rheumatologists, to help more patients achieve a complete and durable response to therapy. The primary endpoint was defined as the proportion of serum uric acid (sUA) responders defined as sUA <6 mg/dL at least 80% of the time during Month 6.¹

Results show that 71% (71 of 100) of patients who were randomized to receive KRYSTEXXA with methotrexate compared to 40% (21 of 52) of patients who were randomized to receive KRYSTEXXA with placebo achieved the primary endpoint (p<0.001). No new safety concerns were identified. These results are aligned with published literature and the prior original pivotal clinical trials of KRYSTEXXA monotherapy which showed 42% (36 of 85) of dosed patients had a complete sUA response and met the primary endpoint of maintaining sUA <6 mg/dL at least 80% of the time in Months 3 and 6.^2,3