The purpose of this study is to investigate the clinical improvement measured by the Glasgow Outcome Scale Extended (GOS-E) with ABX-101 compared with Placebo intramuscular injection in participants with moderate to severe TBI.

Study details include:

• The study duration will be up to 180 days per participant.
• The treatment duration will be up to 7 days.
• The visits post-treatment will be on day 30 and day 180 of the study.

Number of Participants:

A maximum of 45 participants will be enrolled into the study and randomized to each treatment arm in a ratio of 1:1:1. i.e., fifteen participants per arm.

Study Arms and Duration:

Participants will be screened, enrolled and receive the assigned treatment within 12 hours of the primary TBI insult. Enrolled participants will be stratified 1:1 (in each arm) by GCS score (GCS 4-8 in one group and GCS 9 - 12 in the other). The treatment period, which involves 6 hourly, i.e., quarter in die (QID), ABX-101 (1 mg OR 2 mg) intramuscular injections, is seven days. Enrolled participant will continue with the in-hospital standard of care, as decided by the external treating physician, and will be followed up by the study team on days 30 and days 180. The ABX-101 1 mg and 2 mg arm will be enrolled simultaneously.

Inclusion Criteria:

• Written informed consent from patient, patient's legal guardian or legal representative, or deferred consent procedure, according to local requirements

• 18 - 50 years of age, inclusive

• Expected to survive more than 24 hours after admission

• Clearly defined time of injury no more than 12 hours before administration of study drug/placebo

  o Subjects stratified 1:1 (in each arm) by treatment administered 0-12 hrs

• TBI with Glasgow Coma Score (GCS) 4-12 requiring intracranial pressure (ICP) monitoring according to the assessment of the treating physician

  o Subjects stratified 1:1 (in each arm) by GCS 4-8 and GCS 9-12

• Catheter placement (intraventricular or intraparenchymal, only) for monitoring and management of increased ICP

• [Brain computed tomography (CT) showing intracranial parenchymal abnormality and hemodynamically stable]

Exclusion Criteria:

• Penetrating head injury (e.g. missile, stab wound)
• Concurrent, but not pre-existing, spinal cord injury
• Not expected to survive more than 24 hours after admission
• Pregnant, or a positive pregnancy test
• Coma due to an exclusive epidural hematoma (lucid interval and absence of structural brain damage on CT scan)
• Patient pupils are unresponsive (dilation) in both eyes
• The subject has a neurodegenerative disease or other neurological disorder including dementia, Parkinson's disease, multiple sclerosis, seizure disorder, or brain tumors.
• Coma suspected to be primarily due to other causes than head injury (e.g. drug overdose intoxication, drowning/near drowning
• Known or CT scan evidence of pre-existing major cerebral damage
• Any severe concomitant condition (cancer; hematologic, renal, hepatic, coronary disease; major psychiatric disorder; alcohol or drug abuse), that can be ascertained at admission
• Known to have received an experimental drug within 4 weeks prior to current injury
• Patients who cannot be monitored with regard to their recovery (GOS-E and QOLIBRI)