Coversin, a small protein complement C5 inhibitor which prevents the cleavage of C5 by C5 convertase into C5a and C5b, will be used in an open label, non-comparative clinical trial in patients with PNH and proven resistance to eculizumab due to C5 polymorphisms. Patients will be treated with Coversin by daily subcutaneous injection for 6 months in order to determine the safety and efficacy of the drug in these circumstances. If satisfactory control of the PNH is achieved, and at the discretion of the Principal Investigator (PI), patients will have the option of remaining on Coversin and being entered into the long term follow-up study.