Phase III Efficacy and Safety Study of AB103 in the Treatment of Patients With Necrotizing Soft Tissue Infections

Inclusion Criteria:

1. Surgical confirmation of NSTI by attending surgeon;
2. mSOFA score ≥3 (in any one or combination of the 5 major components of SOFA score withone organ component having a score of at least 2: cardiovascular, respiratory, renal,coagulation, CNS), measured as close as possible to the first debridement;
3. IV drug administration within 6 hours from the clinical diagnosis and the decision atthe study site, to have an urgent surgical exploration and debridement (drug shouldnot be administered until surgical confirmation is established);
4. If a woman is of childbearing potential, she must consistently use an acceptablemethod of contraception from baseline through Day 28;
5. If a male patient's sexual partner is of childbearing potential, the male patient mustacknowledge that they will consistently use an acceptable method of contraception (defined above) from baseline through Day 28.
6. Signed and dated informed consent (ICF) as defined by the Institutional Review Board (IRB) and, if applicable, California Bill of Rights. If patient is unable tocomprehend or sign the ICF, patient's legally acceptable representative may sign theICF

Exclusion Criteria:

1. BMI>51;
2. Patient who has been operated at least once for the current NSTI infection and had acurative deep tissue debridement;
3. Patients with overt peripheral vascular disease in the involved area ;
4. Diabetic patients with peripheral vascular disease who present with below the ankleinfection;
5. Removed deep vein thrombosis (DVT) in area of NSTI as an exclusion criteria
6. Patient with burn wounds;
7. Current condition of: (a) Inability to maintain a mean arterial pressure > 50 mmHgand/or systolic blood pressure > 70 mmHg for at least 1 hour prior to screeningdespite the presence of vasopressors and IV fluids or (b) a patient with respiratoryfailure such that an SaO2 of 80% cannot be achieved or (c) a patient with refractorycoagulopathy (INR >5) or thrombocytopenia (platelet count <20,000) that does notpartially correct with administration of appropriate factors or blood products;
8. Chronic neurological impairment that leads to a neuro mSOFA component ≥2;
9. Recent cerebrovascular accident in the last 3 months;
10. Patients with cardiac arrest requiring cardiopulmonary resuscitation within the past 30 days;
11. Patient is not expected to survive throughout 28 days of study due to underlyingmedical condition, such as poorly controlled neoplasm;
12. Patient or patient's family are not committed to aggressive management of thepatient's condition;
13. Any concurrent medical condition, which in the opinion of the Investigator, maycompromise the safety of the patient or the objectives of the study or the patientwill not benefit from treatment such as:

• Congestive heart failure (CHF){ New York Heart Association (NYHA) class III-IV}
• Severe chronic pulmonary obstructive disease (COPD)
• Liver dysfunction {Childs-Pugh class C}
• Immunosuppression (see Appendix F, Section 15.6 for list of excludedimmunosuppressive medications)
• Neutropenia < 1,000 cells/mm3not due to the underlying infection
• Idiopathic Thrombocytopenia Purpura
• Receiving or about to receive chemotherapy or biologic anti-cancer treatmentalthough hormonal manipulation therapies for breast and prostate malignancies arepermitted
• Hematological and lymphatic malignancies in the last 5 years;

14. Known HIV infection with CD4 (cluster of differentiation 4) count < 200 cells/mm3 or < 14% of all lymphocytes;
15. Patients with known chronic kidney disease (documented pre-illness creatinine value(s) ≥2.0) or patients receiving renal replacement therapy for chronic kidney disease;
16. Patients that are treated with continuous hemofiltration (e.g. Continuous Veno-VenousHemofiltration) for acute kidney dysfunction, not due to NSTI, starting prior to studydrug administration;
17. Pregnant or lactating women;
18. Previous enrollment in a clinical trial involving investigational drug or a medicaldevice within 30 days;
19. Previous enrollment in this protocol, ATB-202 or the Phase 2 trial of AB103, ATB-201.