The active substance in Zilbrysq, zilucoplan, is designed to attach to the C5 complement protein, which is part of the immune system called the ‘complement system’.

Myasthenia gravis is caused by the production of autoantibodies (proteins that attack parts of a person’s own body by mistake) that damage acetylcholine receptors, which in normal conditions allow signals from the nerves to trigger muscle contractions. The attachment of autoantibodies to acetylcholine receptors activates the complement system, which leads to damage of the contact point between the nerve and muscle. Due to this damage, the muscles are not able to contract as well as normal, leading to muscle weakness and difficulty moving. By attaching to the C5 complement protein, zilucoplan reduces the activity of the complement system, which decreases the damage of acetylcholine receptors thereby improving the symptoms of the disease.