Ultomiris (ravulizumab-cwvz) is a humanized monoclonal antibody developed by Alexion to treat atypical hemolytic uremic syndrome (aHUS).

The U.S. and the EU both approved the treatment for adults and children with aHUS. The U.S., EU, and Japan have also approved Ultomiris to treat paroxysmal nocturnal hemoglobinuria, a disease characterized by the excessive breakdown of red blood cells.

The therapy is not indicated for the treatment of typical or STEC HUS, which is caused by Shiga toxins that are produced by E. coli bacteria.

How does Ultomiris work?

The immune system uses the complement pathway to mark pathogens for targeted destruction. In aHUS, mutations in complement pathway genes, such as CFHMCP (CD46), and CFI, lead to the uncontrolled activation of the alternative complement pathway. This leads to thrombotic microangiopathy (TMA) or blood clots in small blood vessels.

The alternative complement pathway is characterized by the cleavage of the complement protein C5 into C5a and C5b fragments. C5a is a molecule that promotes inflammation. C5b combines with other proteins to form a terminal membrane complex called C5b-9, which, in turn, promotes clotting within blood vessels by aggregating platelets.

The mechanism of action of Ultomiris is similar to that of Soliris (eculizumab) — also developed by Alexion and approved to treat aHUS. Both medications inhibit the cleavage of the complement factor C5 into C5a and C5b, thereby preventing the formation of the C5b-9 complex and clots within blood vessels. Ultomiris does not affect the earlier components of the complement pathway and, therefore, does not compromise immunity against pathogens.

Ultomiris in clinical trials

An ongoing Phase 3 clinical trial (NCT02949128), called aHUS-311, is studying the safety and efficacy of Ultomiris in 58 adolescent and adult aHUS patients, who have not previously received any complement inhibitor. Researchers expect to complete the trial in July 2023.

Top-line results from the study showed that patients tolerated Ultomiris well. The trial also met its primary objective of achieving a complete TMA response in 53.6% of patients after an initial 26-week treatment period. A complete TMA response is characterized by reduced hemolytic anemia (loss of red blood cells) that researchers measure by the normalization of lactate dehydrogenase (LDH) levels; reduced thrombocytopenia (low platelet count), which is measured by normalization in platelet count; and better kidney function that’s measured by an improvement of more than 25% in serum creatinine level from baseline.

Another Phase 3 clinical trial (NCT03131219), called aHUS-312, is assessing the safety and efficacy of Ultomiris in children and adolescents with aHUS. Researchers expect to complete the trial in May 2025.

Data from an interim analysis of 14 participants showed that 71% of patients met the primary goal of the trial by achieving a complete TMA response within the first 26 weeks of treatment. The results also showed that 93% of the children achieved normalization in platelet counts. Moreover, 86% achieved normalization in LDH levels, and 79% showed significant improvement in kidney function.

Other information

The dosage of Ultomiris is based on the patient’s body weight. Doctors administer the treatment directly into the bloodstream once every eight weeks in adults and once every four to eight weeks in children. Four point mutations in the sequence of Ultomiris extend its half-life, allowing the medication to remain active for longer periods of time. Therefore, patients require less frequent dosing with Ultomiris than with Soliris, which doctors administer once every two weeks.

Alexion is also evaluating the safety and effectiveness of self-administered, weekly under-the-skin injections of Ultomiris in adults with PNH. The company expects that these data will support regulatory submissions to health authorities seeking the approval of this formulation, administered through a patient-friendly device, for both PNH and aHUS.

In the EU, Ultomiris’ indication includes patients who have never used a complement inhibitor and those who’ve been receiving Soliris for at least three months and are responding to it.

Patients on Ultomiris are at a higher risk of acquiring life-threatening meningococcal infections and must receive an immunization at least two weeks before starting therapy.

Ultomiris is only available through the FDA’s risk evaluation and mitigation strategy program, which requires a specially certified healthcare provider to evaluate whether the benefits of the therapy outweigh the risks of serious side effects.


Last updated: July 6, 2020


aHUS News is strictly a news and information website about the disease. It does not provide medical advice, diagnosis, or treatment. This content is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read on this website.

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Özge has a MSc. in Molecular Genetics from the University of Leicester and a PhD in Developmental Biology from Queen Mary University of London. She worked as a Post-doctoral Research Associate at the University of Leicester for six years in the field of Behavioural Neurology before moving into science communication. She worked as the Research Communication Officer at a London based charity for almost two years.