Satralizumab (brand name Enspryng) is a humanized monoclonal antibody medication. It functions as an interleukin-6 (IL-6) receptor inhibitor, designed to modulate the immune system. Approved in the United States in August 2020 and the European Union in June 2021, satralizumab addresses certain autoimmune processes.
Treating Neuromyelitis Optica Spectrum Disorder
Satralizumab is approved for treating neuromyelitis optica spectrum disorder (NMOSD) in adults who test positive for aquaporin-4 (AQP4) antibodies. NMOSD is a rare, chronic autoimmune disease affecting the central nervous system, including the brain, optic nerves, and spinal cord. Unlike multiple sclerosis, NMOSD primarily targets the optic nerves and spinal cord, leading to distinct symptoms.
In NMOSD, the immune system mistakenly attacks healthy cells, particularly those in the optic nerves and spinal cord. This attack often targets aquaporin-4 (AQP4), triggering inflammation and damage.
The disease can manifest with optic neuritis, causing eye pain and sudden vision loss. It also frequently leads to myelitis, an inflammation of the spinal cord, resulting in muscle weakness, paralysis, or problems with sensation or bladder control. Approximately half of those affected experience permanent visual impairment or paralysis. NMOSD is more common in women, with onset typically between 30 and 40 years of age, affecting an estimated 4,000 to 8,000 Americans.
How Satralizumab Works
Satralizumab targets the interleukin-6 (IL-6) receptor. IL-6 is a cytokine that plays a significant role in inflammation and immune responses; elevated levels are often found in NMOSD during active disease.
The medication binds to both soluble and membrane-bound IL-6 receptors, preventing IL-6 from initiating its pro-inflammatory signaling. This action reduces inflammation and modulates the immune response contributing to NMOSD pathology.
Blocking the IL-6 pathway helps manage NMOSD by decreasing IL-6-mediated autoimmune T- and B-cell activation, including preventing the secretion of AQP4-IgG autoantibodies. Satralizumab’s action may also counteract IL-6’s contribution to increased blood-brain barrier permeability. The drug utilizes a “recycling antibody technology” which allows it to dissociate from the IL-6 receptor in acidic environments within cells, enabling it to bind to another receptor after being released back into the bloodstream, thereby extending its duration of action.
Administration and Monitoring
Satralizumab is administered as a subcutaneous injection. The typical dosing regimen involves an initial loading phase of 120 milligrams (mg) injected every two weeks for three doses. A maintenance dose of 120 mg is then given once every four weeks.
The medication is provided in single-dose prefilled syringes, suitable for home administration after training. Patients or caregivers are instructed on preparation, injection sites (abdomen or thigh), and site rotation.
Regular medical monitoring is important. Blood tests are needed to check for liver enzyme levels and neutrophil counts. Liver enzymes (ALT and AST) should be monitored every four weeks for the first three months, then every three months for one year, and thereafter as clinically indicated. Neutrophil counts should be checked four to eight weeks after starting therapy and at regular intervals afterward. Screening for hepatitis B and tuberculosis is done before starting treatment.
Potential Side Effects
Satralizumab can cause side effects. Common reactions include nasopharyngitis, headache, upper respiratory tract infections, rash, joint pain, pain in extremities, fatigue, nausea, and gastritis.
More serious, less common side effects require immediate medical attention. These include signs of serious allergic reaction (hives, light-headedness, difficulty breathing, facial swelling) and increased risk of serious infections. Patients should contact their doctor for infection symptoms like fever, chills, or persistent cough.
Elevated liver enzymes and decreased neutrophil counts are risks, monitored via blood tests. Rare cases of hepatitis B virus reactivation or tuberculosis infection can occur, requiring screening before treatment.
What to Expect from Treatment
Satralizumab treatment aims to reduce the frequency and severity of NMOSD relapses. Clinical studies show positive effects in reducing relapse risk, especially for AQP4 antibody-positive individuals. For example, monotherapy reduced NMOSD relapses by 74% in AQP4-positive participants compared to placebo over 96 weeks.
In combination with immunosuppressant treatment, satralizumab significantly reduced relapse rates. One study showed an 80% reduction in relapses for AQP4-positive participants compared to immunosuppressant treatment alone. These reductions contribute to a more stable disease course and help preserve neurological function.
Patients may experience improved quality of life due to fewer attacks and better disease control. Treatment aims to minimize NMOSD’s impact on daily life and prevent further damage. Satralizumab provides a beneficial option for managing NMOSD in eligible patients.