Rystiggo, Zilbrysq cleared in UK for adults with generalized MG

More regulatory decisions are expected in other countries this year

Lindsey Shapiro, PhD avatar

by Lindsey Shapiro, PhD |

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Regulators in the U.K. have approved UCB’s Rystiggo (rozanolixizumab) as an add-on treatment for adults with generalized myasthenia gravis (gMG) who are positive for antibodies that target the acetylcholine receptor (AChR) or muscle-specific tyrosine kinase (MuSK).

The decision from the Medicines and Healthcare products Regulatory Agency (MHRA) comes less than two months after UCB’s other gMG therapy, Zilbrysq (zilucoplan), was cleared as an add-on treatment in adults positive for anti-AChR antibodies.

The MHRA said it will continue to monitor Rystiggo’s safety and efficacy, as it does with any newly approved medication, it noted.

“Patient safety is always our priority, which means enabling their access to high quality, safe and effective medical products,” Julian Beach, interim executive director of MHRA, said in a press release. “We’re assured that the appropriate regulatory standards for the approval of this medicine have been met.”

Rystiggo and Zilbrysq are cleared for similar patient populations in the U.S. and European Union. The treatments are also cleared in Japan, but only for patients who haven’t adequately responded to steroids or other immunosuppressant medications.

Both remain under review in other countries and additional regulatory decisions are expected this year.

People with gMG have muscle weakness and fatigue due to self-reactive immune attacks that damage the neuromuscular junction, the region where nerve and muscle cells communicate to coordinate movement. These attacks are mediated by antibodies that target important neuromuscular proteins, including AChRs and MuSK.

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How Rystiggo, Zilbrysq work in gMG

Rystiggo is designed to speed the breakdown of these self-reactive antibodies and lower their levels by inhibiting neonatal Fc receptor, a protein that works to prevent their degradation.

The medication is given via infusions under the skin, or subcutaneously, once weekly for six weeks, after which additional treatment cycles are determined based on a patient’s response.

In the Phase 3 MycarinG study (NCT03971422), Rystiggo led to reductions in measures of disease severity compared with a placebo among patients with either anti-MuSK or anti-AChR antibodies, a finding that backed its clearance for these populations.

Zilbrysq targets the C5 protein, a component of the immune system’s complement cascade that’s involved in driving the damaging effects of gMG-causing antibodies. By blocking the cascade’s activation, the medication should prevent damage to neuromuscular junctions, easing disease severity.

Approval of the once-daily subcutaneous medication was supported by findings from the Phase 3 RAISE trial (NCT04115293), where Zilbrysq led to significant reductions in symptom severity and increased quality of life relative to a placebo among patients with anti-AChR antibodies.

Common side effects of Rystiggo include headache, diarrhea, and fever. Zilbrysq’s side effects include injection site reactions, upper respiratory tract infections, and diarrhea.

Patients who suspect they’re having side effects from Rystiggo or any other medication should let their healthcare providers know and report them to the MHRA Yellow Card scheme, the U.K.’s system for recording adverse events from real-world medication use, according to the MHRA.