Eculizumab

Eculizumab is a humanized monoclonal antibody and terminal complement inhibitor that binds to complement protein C5. By preventing the cleavage of C5 into C5a and C5b, it inhibits formation of the terminal complement complex that can damage blood cells, vascular endothelium and other tissues. This mechanism is clinically relevant in disorders in which uncontrolled complement activation contributes substantially to disease. Eculizumab is administered by intravenous infusion under the supervision of a healthcare professional. It is used in several rare disorders, including paroxysmal nocturnal hemoglobinuria (PNH), atypical hemolytic uremic syndrome (aHUS), anti-acetylcholine receptor antibody-positive generalized myasthenia gravis (gMG), and anti-aquaporin-4 antibody-positive neuromyelitis optica spectrum disorder (NMOSD), with age and indication requirements varying by regulatory authority. By suppressing terminal complement activity, eculizumab can reduce complement-mediated red-cell destruction in PNH, inhibit complement-mediated thrombotic microangiopathy in aHUS, and reduce complement-associated neuromuscular or neurological injury in selected antibody-positive disorders. Because terminal complement activity is also important in defense against certain encapsulated bacteria, particularly Neisseria meningitidis, treatment requires specific infection-prevention measures and careful clinical monitoring.

Eculizumab was developed as a recombinant humanized monoclonal antibody directed against complement component C5. The U.S. FDA granted the original approval for Soliris on March 16, 2007 for PNH to reduce hemolysis. FDA subsequently granted accelerated approval for aHUS in 2011, converted to regular approval in 2014, followed by approval for adult anti-AChR antibody-positive generalized myasthenia gravis in 2017 and adult anti-AQP4 antibody-positive NMOSD in 2019. In February 2025, the FDA expanded the gMG indication to include pediatric patients aged 6 years and older who are anti-AChR antibody positive. The EMA granted marketing authorisation for Soliris on June 20, 2007, initially for PNH, with subsequent indications added for aHUS, refractory generalized myasthenia gravis and AQP4-positive NMOSD. Key clinical development programs included the TRIUMPH and related PNH studies, prospective aHUS studies, the phase 3 REGAIN trial in generalized myasthenia gravis, and the phase 3 PREVENT trial in NMOSD. India’s CDSCO has also approved eculizumab presentations for PNH and aHUS, with regulatory recommendations concerning specialist prescribing and monitoring.

Eculizumab is used to reduce hemolysis in patients with PNH and to inhibit complement-mediated thrombotic microangiopathy in patients with aHUS. It is not indicated for Shiga toxin-producing Escherichia coli-associated hemolytic uremic syndrome (STEC-HUS). In the United States, eculizumab is also approved for generalized myasthenia gravis in anti-AChR antibody-positive adults and children aged 6 years and older, and for NMOSD in anti-AQP4 antibody-positive adults. The EMA authorizes Soliris for PNH and aHUS in adults and children and for refractory anti-AChR antibody-positive generalized myasthenia gravis in patients aged 6 years and above, as well as AQP4-positive NMOSD in adults with a relapsing course. Eculizumab may be used alongside other therapies depending on the underlying condition; for example, patients with gMG or NMOSD may continue appropriate background immunosuppressive treatment when clinically indicated.

Eculizumab is administered only by intravenous infusion, with the dose and schedule determined by the indication and, for pediatric aHUS, body weight. In adults with PNH, the U.S. regimen consists of weekly induction doses followed by a maintenance dose every two weeks. Adult aHUS, gMG and NMOSD regimens use a higher weekly induction schedule followed by maintenance dosing every two weeks. Pediatric aHUS dosing is weight based and may use maintenance intervals of two or three weeks depending on body weight. Eculizumab infusions are generally administered over approximately 35 minutes in adults, with longer infusion periods used in pediatric patients. Patients should be observed during infusion and for at least one hour afterward for infusion-related reactions. Supplemental dosing may be required when patients undergo plasmapheresis, plasma exchange or fresh frozen plasma infusion. Treatment is generally long term for chronic complement-mediated disorders unless discontinuation is clinically indicated.

Common adverse effects vary somewhat by the underlying disease and clinical trial population. Reported effects include headache, nasopharyngitis, back pain, nausea, diarrhea, upper respiratory infections, abdominal pain, vomiting, hypertension, anemia, cough, peripheral edema, urinary tract infections, fever, dizziness, influenza-like illness, joint pain and musculoskeletal pain. Infusion-related reactions can also occur. Because eculizumab suppresses terminal complement activity, infections are an important safety consideration even when routine adverse effects are mild. Patients receiving long-term therapy should report new or persistent symptoms promptly so that infection and other complications can be assessed.

The major safety warning associated with eculizumab is the increased risk of serious, life-threatening or fatal meningococcal infection caused by Neisseria meningitidis. Patients may develop invasive infection despite appropriate vaccination, so vaccination does not eliminate the need for clinical vigilance. Eculizumab should not be initiated in patients with unresolved serious meningococcal infection. Other serious infections, including infections caused by other Neisseria species, can occur. Infusion-related reactions may require slowing or stopping the infusion and appropriate supportive treatment. Disease manifestations can recur after treatment is discontinued, including hemolysis in PNH and complement-mediated disease activity in other indications, so discontinuation requires careful clinical planning. In PNH, thrombosis risk and disease activity should continue to be assessed during treatment and after discontinuation.

Before treatment, clinicians should confirm the indication and relevant disease-specific laboratory or antibody testing, assess vaccination status, and evaluate for active infection. Meningococcal vaccination covering the recommended serogroups should be completed before treatment whenever possible; when urgent therapy is required before vaccination can be completed, antibacterial prophylaxis may be considered according to applicable guidance. Patients receiving long-term complement inhibition require ongoing vaccination and infection-risk assessment. Eculizumab is a monoclonal antibody and is not primarily metabolized through conventional cytochrome P450 pathways, so classic metabolic drug interactions are generally uncommon. However, plasmapheresis, plasma exchange and fresh frozen plasma can remove or dilute eculizumab and require supplemental dosing. Neonatal Fc receptor blockers may also affect eculizumab exposure and should be considered when therapies are combined. Pregnancy, breastfeeding, pediatric use and immunization decisions should be assessed according to the individual product labeling and clinical circumstances.

Confirm the disease-specific indication, antibody status where required, baseline laboratory findings and meningococcal vaccination status before starting treatment. Ensure patients understand that vaccination reduces but does not eliminate the risk of meningococcal disease and that symptoms such as fever, headache, neck stiffness, rash, confusion or other signs of serious infection require immediate medical evaluation. Review the need for antibacterial prophylaxis when urgent treatment must begin before vaccination requirements are met. Eculizumab should be prepared and administered according to product-specific instructions and given only by intravenous infusion; patients should be observed during and after administration for infusion-related reactions. Monitor disease-specific markers such as hemolysis parameters in PNH and hematologic or renal measures in aHUS, together with clinical disease activity in gMG or NMOSD. Coordinate care with hematology, nephrology, neurology, pharmacy and vaccination services when appropriate, particularly when treatment interruption, plasma exchange or transition to another complement inhibitor is being considered.