Table 1 Inclusion and exclusion criteria

Inclusion criteria

 • SAH confirmed by CT and aneurysm by CTA or DSA

 • Admission to the UMC Utrecht < 12 h after ictus

 • Age 18 years and older

Exclusion criteria

 • Life expectancy < 10 days

 • Pregnant or breastfeeding women

 • Participation in another clinical therapeutic study

 • History of splenectomy or asplenia

 • Haematologic malignancy

 • Patients receiving chemotherapy

 • Patients who will undergo or underwent an organ transplantation

 • Patients with myasthenia gravis, glucose-6-phosphate dehydrogenase (G6PD) deficiency, or tuberculosis

 • Patients who are or will be treated by plasmapheresis or haemodialysis

 • Patient with a creatinine clearance of < 30 or serum creatinine levels of > 169 μmol/l

 • Patients with a known hereditary complement deficiency

 • Patients allergic to eculizumab, proteins derived from mouse products, or other monoclonal antibodies

 • Patients allergic to (prophylactic) antibiotic treatment for Neisseria meningitidis (quinolones or ceftriaxone)

 • If on admission, it is likely that the aneurysm can only be treated with extracranial-intracranial bypass surgery

 • If based on head imaging, it will be unlikely that CSF can be obtained at day 3 after ictus

 • Patients with an ongoing infection on admission which is not appropriately treated

 • Patients who were treated > 4 times with antibiotics during the last year

 • Patients on immunosuppressive therapy