Pharmacological Management of Atypical Hemolytic Uremic Syndrome in Pediatric Patients: Current and Future

Abstract

Atypical hemolytic uremic syndrome is a thrombotic microangiopathy characterized by hemolysis, thrombocytopenia, and acute kidney injury, usually caused by alternative complement system overactivation due to pathogenic genetic variants or antibodies to components or regulatory factors in this pathway. Previously, a lack of effective treatment for this condition was associated with mortality, end-stage kidney disease, and the risk of disease recurrence after kidney transplantation. Plasma therapy has been used for atypical hemolytic uremic syndrome treatment with inconsistent results. Complement-blocking treatment changed the outcome and prognosis of patients with atypical hemolytic uremic syndrome. Early administration of eculizumab, a monoclonal C5 antibody, leads to improvements in hematologic, kidney, and systemic manifestations in patients with atypical hemolytic uremic syndrome, even with apparent dialysis dependency. Pre- and post-transplant use of eculizumab is effective in the prevention of atypical hemolytic uremic syndrome recurrence. Evidence on eculizumab use in secondary hemolytic uremic syndrome cases is controversial. Recent data favor the restrictive use of eculizumab in carefully selected atypical hemolytic uremic syndrome cases, but close monitoring for relapse after drug discontinuation is emphasized. Prophylaxis for meningococcal infection is important. The long-acting C5 monoclonal antibody ravulizumab is now approved for atypical hemolytic uremic syndrome treatment, enabling a reduction in the dosing frequency and improving the quality of life in patients with atypical hemolytic uremic syndrome. New strategies for additional and novel complement blockage medications in atypical hemolytic uremic syndrome are under investigation.

Fig. 1

Simplified alternative complement cascade and its regulation. Complement components: filled squares (basic: blue; activated: orange). Cofactors for this pathway activation: red ovals; regulators (FH, FI, membrane cofactor protein, DAF, CD59): green triangles. The active products of this cascade (C3a, C5a, and C5b-9): yellow circles. Pathogenic genetic variants and antibodies leading to its over-activation: green squares. Sites of pharmacologic complement inhibition for aHUS treatment: white squares. Activating factors: FB factor B, FD factor D, P properdin. Regulatory factors: anti-FH Ab-anti-factor H antibodies, DAF-decay-accelerating factor, FH factor H, FI factor I, MCP membrane cofactor protein