40 mg/kg placebo, single dose (day 0), Group 4

40 mg/kg intravenously, single dose, day 0, Group 2

Liver function parameters were assessed using the modified Division of Microbiology and Infectious Diseases (DMID) toxicity tables, version 2.0. Grade 1 (Mild): Transient or mild discomfort (< 48 hours); no medical intervention or therapy required. Grade 2 (Moderate): Mild to moderate limitation in activity, some assistance may be needed; no or minimal medical intervention or therapy required. Grade 3 (Severe): Marked limitation in activity, some assistance usually required; medical intervention or therapy required, hospitalizations possible. Grade 4 (Life-threatening): Extreme limitation in activity, significant assistance required; significant medical intervention or therapy required, hospitalization or hospice care probable.

The number of participants with at least a 2-grade worsening from Baseline in liver toxicities were assessed. Liver function parameters were assessed using the modified Division of Microbiology and Infectious Diseases (DMID) toxicity tables, version 2.0. Grade 1 (Mild): Transient or mild discomfort (< 48 hours); no medical intervention or therapy required. Grade 2 (Moderate): Mild to moderate limitation in activity, some assistance may be needed; no or minimal medical intervention or therapy required. Grade 3 (Severe): Marked limitation in activity, some assistance usually required; medical intervention or therapy required, hospitalizations possible. Grade 4 (Life-threatening): Extreme limitation in activity, significant assistance required; significant medical intervention or therapy required, hospitalization or hospice care probable. Baseline is defined as the value of the variable measured at Day 0 prior to dosing.

Electrolyte function parameters were assessed using the modified Division of Microbiology and Infectious Diseases (DMID) toxicity tables, version 2.0. Grade 1 (Mild): Transient or mild discomfort (< 48 hours); no medical intervention or therapy required. Grade 2 (Moderate): Mild to moderate limitation in activity, some assistance may be needed; no or minimal medical intervention or therapy required. Grade 3 (Severe): Marked limitation in activity, some assistance usually required; medical intervention or therapy required, hospitalizations possible. Grade 4 (Life-threatening): Extreme limitation in activity, significant assistance required; significant medical intervention or therapy required, hospitalization or hospice care probable.

The number of participants with at least a 2-grade worsening from Baseline in electrolyte toxicities were assessed. Electrolyte function parameters were assessed using the modified Division of Microbiology and Infectious Diseases (DMID) toxicity tables, version 2.0. Grade 1 (Mild): Transient or mild discomfort (< 48 hours); no medical intervention or therapy required. Grade 2 (Moderate): Mild to moderate limitation in activity, some assistance may be needed; no or minimal medical intervention or therapy required. Grade 3 (Severe): Marked limitation in activity, some assistance usually required; medical intervention or therapy required, hospitalizations possible. Grade 4 (Life-threatening): Extreme limitation in activity, significant assistance required; significant medical intervention or therapy required, hospitalization or hospice care probable. Baseline is defined as the value of the variable measured at Day 0 prior to dosing.

Other chemistry parameters were assessed using the modified Division of Microbiology and Infectious Diseases (DMID) toxicity tables, version 2.0. Grade 1 (Mild): Transient or mild discomfort (< 48 hours); no medical intervention or therapy required. Grade 2 (Moderate): Mild to moderate limitation in activity, some assistance may be needed; no or minimal medical intervention or therapy required. Grade 3 (Severe): Marked limitation in activity, some assistance usually required; medical intervention or therapy required, hospitalizations possible. Grade 4 (Life-threatening): Extreme limitation in activity, significant assistance required; significant medical intervention or therapy required, hospitalization or hospice care probable.

The number of participants with at least a 2-grade worsening from Baseline in other chemistry toxicities were assessed. Other clinical chemistry parameters were assessed using the modified Division of Microbiology and Infectious Diseases (DMID) toxicity tables, version 2.0. Grade 1 (Mild): Transient or mild discomfort (< 48 hours); no medical intervention or therapy required. Grade 2 (Moderate): Mild to moderate limitation in activity, some assistance may be needed; no or minimal medical intervention or therapy required. Grade 3 (Severe): Marked limitation in activity, some assistance usually required; medical intervention or therapy required, hospitalizations possible. Grade 4 (Life-threatening): Extreme limitation in activity, significant assistance required; significant medical intervention or therapy required, hospitalization or hospice care probable. Baseline is defined as the value of the variable measured at Day 0 prior to dosing.

Clinical thyroid parameters were assessed using the modified Division of Microbiology and Infectious Diseases (DMID) toxicity tables, version 2.0. Grade 1 (Mild): Transient or mild discomfort (< 48 hours); no medical intervention or therapy required. Grade 2 (Moderate): Mild to moderate limitation in activity, some assistance may be needed; no or minimal medical intervention or therapy required. Grade 3 (Severe): Marked limitation in activity, some assistance usually required; medical intervention or therapy required, hospitalizations possible. Grade 4 (Life-threatening): Extreme limitation in activity, significant assistance required; significant medical intervention or therapy required, hospitalization or hospice care probable.

Urinaysis parameters were assessed using the modified Division of Microbiology and Infectious Diseases (DMID) toxicity tables, version 2.0. Grade 1 (Mild): Transient or mild discomfort (< 48 hours); no medical intervention or therapy required. Grade 2 (Moderate): Mild to moderate limitation in activity, some assistance may be needed; no or minimal medical intervention or therapy required. Grade 3 (Severe): Marked limitation in activity, some assistance usually required; medical intervention or therapy required, hospitalizations possible. Grade 4 (Life-threatening): Extreme limitation in activity, significant assistance required; significant medical intervention or therapy required, hospitalization or hospice care probable.

Urinalysis parameters were assessed using the modified Division of Microbiology and Infectious Diseases (DMID) toxicity tables, version 2.0. Grade 1 (Mild): Transient or mild discomfort (< 48 hours); no medical intervention or therapy required. Grade 2 (Moderate): Mild to moderate limitation in activity, some assistance may be needed; no or minimal medical intervention or therapy required. Grade 3 (Severe): Marked limitation in activity, some assistance usually required; medical intervention or therapy required, hospitalizations possible. Grade 4 (Life-threatening): Extreme limitation in activity, significant assistance required; significant medical intervention or therapy required, hospitalization or hospice care probable. Baseline is defined as the value of the variable measured at Day 0 prior to dosing.

Number of participants who developed an anti-raxibacumab antibody response during the study were assessed. .Immunogenicity testing was performed to determine if raxibacumab induced an anti-raxibacumab immune response. Testing comprised of 2 assays (screening and confirmatory). The screening assay (direct binding) was an electrochemiluminescence (ECL)-based bridging assay. A rabbit polyclonal antibody was used as a positive control. Samples above the assay cut point were considered positive. Samples identified as positive in the screening assay were confirmed positive in a confirmatory assay. Samples must have demonstrated a significant percent drop in the confirmatory inhibition of binding assay to be considered positive. The inhibition of binding confirmatory assay was performed identically to the direct binding screening assay with the exception that the samples were tested in parallel with excess unlabeled raxibacumab.

Blood was collected from each participant at selected times post dose, and serum specimens were analyzed for raxibacumab using a validated electrochemiluminescense-based assay. The individual serum raxibacumab concentration data were summarized by nominal collection time and treatment group using descriptive statistics. For the participants that received two doses, blood samples for serum raxibacumab concentration measurement were collected from participants prior to administration of the raxibacumab and diphenhydramine doses on Days 0 and 14, at 30 minutes and 2 to 6 hours after completion of each raxibacumab infusion, and at 28, 42, 56, and 70 days after the 1st raxibacumab dose.

Participants received a single dose of 40 mg/kilogram (kg) raxibacumab administered via IV infusion. Participants were treated with oral diphenhydramine (25-50 mg) up to 60 minutes prior to infusion of raxibacumab.

Participants received a double dose of 40 mg/kg raxibacumab administered 14 days apart via IV infusion. Participants were treated with oral diphenhydramine (25-50 mg) up to 60 minutes prior to infusion of raxibacumab.

Total of all reporting groups

Clinical hematological parameters were assessed using the modified Division of Microbiology and Infectious Diseases (DMID) toxicity tables, version 2.0. Grade 1 (Mild): Transient or mild discomfort (< 48 hours); no medical intervention or therapy required. Grade 2 (Moderate): Mild to moderate limitation in activity, some assistance may be needed; no or minimal medical intervention or therapy required. Grade 3 (Severe): Marked limitation in activity, some assistance usually required; medical intervention or therapy required, hospitalizations possible. Grade 4 (Life-threatening): Extreme limitation in activity, significant assistance required; significant medical intervention or therapy required, hospitalization or hospice care probable.

As-treated population

The number of participants with at least a 2-grade worsening from Baseline in hematological toxicities were assessed. Clinical hematological parameters were assessed using the modified Division of Microbiology and Infectious Diseases (DMID) toxicity tables, version 2.0. Grade 1 (Mild): Transient or mild discomfort (< 48 hours); no medical intervention or therapy required. Grade 2 (Moderate): Mild to moderate limitation in activity, some assistance may be needed; no or minimal medical intervention or therapy required. Grade 3 (Severe): Marked limitation in activity, some assistance usually required; medical intervention or therapy required, hospitalizations possible. Grade 4 (Life-threatening): Extreme limitation in activity, significant assistance required; significant medical intervention or therapy required, hospitalization or hospice care probable. Baseline is defined as the value of the variable measured at Day 0 prior to dosing.

As-treated population

Liver function parameters were assessed using the modified Division of Microbiology and Infectious Diseases (DMID) toxicity tables, version 2.0. Grade 1 (Mild): Transient or mild discomfort (< 48 hours); no medical intervention or therapy required. Grade 2 (Moderate): Mild to moderate limitation in activity, some assistance may be needed; no or minimal medical intervention or therapy required. Grade 3 (Severe): Marked limitation in activity, some assistance usually required; medical intervention or therapy required, hospitalizations possible. Grade 4 (Life-threatening): Extreme limitation in activity, significant assistance required; significant medical intervention or therapy required, hospitalization or hospice care probable.

As-treated population

The number of participants with at least a 2-grade worsening from Baseline in liver toxicities were assessed. Liver function parameters were assessed using the modified Division of Microbiology and Infectious Diseases (DMID) toxicity tables, version 2.0. Grade 1 (Mild): Transient or mild discomfort (< 48 hours); no medical intervention or therapy required. Grade 2 (Moderate): Mild to moderate limitation in activity, some assistance may be needed; no or minimal medical intervention or therapy required. Grade 3 (Severe): Marked limitation in activity, some assistance usually required; medical intervention or therapy required, hospitalizations possible. Grade 4 (Life-threatening): Extreme limitation in activity, significant assistance required; significant medical intervention or therapy required, hospitalization or hospice care probable. Baseline is defined as the value of the variable measured at Day 0 prior to dosing.

As-treated population

Electrolyte function parameters were assessed using the modified Division of Microbiology and Infectious Diseases (DMID) toxicity tables, version 2.0. Grade 1 (Mild): Transient or mild discomfort (< 48 hours); no medical intervention or therapy required. Grade 2 (Moderate): Mild to moderate limitation in activity, some assistance may be needed; no or minimal medical intervention or therapy required. Grade 3 (Severe): Marked limitation in activity, some assistance usually required; medical intervention or therapy required, hospitalizations possible. Grade 4 (Life-threatening): Extreme limitation in activity, significant assistance required; significant medical intervention or therapy required, hospitalization or hospice care probable.

As-treated population

The number of participants with at least a 2-grade worsening from Baseline in electrolyte toxicities were assessed. Electrolyte function parameters were assessed using the modified Division of Microbiology and Infectious Diseases (DMID) toxicity tables, version 2.0. Grade 1 (Mild): Transient or mild discomfort (< 48 hours); no medical intervention or therapy required. Grade 2 (Moderate): Mild to moderate limitation in activity, some assistance may be needed; no or minimal medical intervention or therapy required. Grade 3 (Severe): Marked limitation in activity, some assistance usually required; medical intervention or therapy required, hospitalizations possible. Grade 4 (Life-threatening): Extreme limitation in activity, significant assistance required; significant medical intervention or therapy required, hospitalization or hospice care probable. Baseline is defined as the value of the variable measured at Day 0 prior to dosing.

As-treated population

Other chemistry parameters were assessed using the modified Division of Microbiology and Infectious Diseases (DMID) toxicity tables, version 2.0. Grade 1 (Mild): Transient or mild discomfort (< 48 hours); no medical intervention or therapy required. Grade 2 (Moderate): Mild to moderate limitation in activity, some assistance may be needed; no or minimal medical intervention or therapy required. Grade 3 (Severe): Marked limitation in activity, some assistance usually required; medical intervention or therapy required, hospitalizations possible. Grade 4 (Life-threatening): Extreme limitation in activity, significant assistance required; significant medical intervention or therapy required, hospitalization or hospice care probable.

As-treated population

The number of participants with at least a 2-grade worsening from Baseline in other chemistry toxicities were assessed. Other clinical chemistry parameters were assessed using the modified Division of Microbiology and Infectious Diseases (DMID) toxicity tables, version 2.0. Grade 1 (Mild): Transient or mild discomfort (< 48 hours); no medical intervention or therapy required. Grade 2 (Moderate): Mild to moderate limitation in activity, some assistance may be needed; no or minimal medical intervention or therapy required. Grade 3 (Severe): Marked limitation in activity, some assistance usually required; medical intervention or therapy required, hospitalizations possible. Grade 4 (Life-threatening): Extreme limitation in activity, significant assistance required; significant medical intervention or therapy required, hospitalization or hospice care probable. Baseline is defined as the value of the variable measured at Day 0 prior to dosing.

As-treated population

Clinical thyroid parameters were assessed using the modified Division of Microbiology and Infectious Diseases (DMID) toxicity tables, version 2.0. Grade 1 (Mild): Transient or mild discomfort (< 48 hours); no medical intervention or therapy required. Grade 2 (Moderate): Mild to moderate limitation in activity, some assistance may be needed; no or minimal medical intervention or therapy required. Grade 3 (Severe): Marked limitation in activity, some assistance usually required; medical intervention or therapy required, hospitalizations possible. Grade 4 (Life-threatening): Extreme limitation in activity, significant assistance required; significant medical intervention or therapy required, hospitalization or hospice care probable.

As-treated population

Urinaysis parameters were assessed using the modified Division of Microbiology and Infectious Diseases (DMID) toxicity tables, version 2.0. Grade 1 (Mild): Transient or mild discomfort (< 48 hours); no medical intervention or therapy required. Grade 2 (Moderate): Mild to moderate limitation in activity, some assistance may be needed; no or minimal medical intervention or therapy required. Grade 3 (Severe): Marked limitation in activity, some assistance usually required; medical intervention or therapy required, hospitalizations possible. Grade 4 (Life-threatening): Extreme limitation in activity, significant assistance required; significant medical intervention or therapy required, hospitalization or hospice care probable.

As-treated population

Urinalysis parameters were assessed using the modified Division of Microbiology and Infectious Diseases (DMID) toxicity tables, version 2.0. Grade 1 (Mild): Transient or mild discomfort (< 48 hours); no medical intervention or therapy required. Grade 2 (Moderate): Mild to moderate limitation in activity, some assistance may be needed; no or minimal medical intervention or therapy required. Grade 3 (Severe): Marked limitation in activity, some assistance usually required; medical intervention or therapy required, hospitalizations possible. Grade 4 (Life-threatening): Extreme limitation in activity, significant assistance required; significant medical intervention or therapy required, hospitalization or hospice care probable. Baseline is defined as the value of the variable measured at Day 0 prior to dosing.

As-treated population

Number of participants who developed an anti-raxibacumab antibody response during the study were assessed. .Immunogenicity testing was performed to determine if raxibacumab induced an anti-raxibacumab immune response. Testing comprised of 2 assays (screening and confirmatory). The screening assay (direct binding) was an electrochemiluminescence (ECL)-based bridging assay. A rabbit polyclonal antibody was used as a positive control. Samples above the assay cut point were considered positive. Samples identified as positive in the screening assay were confirmed positive in a confirmatory assay. Samples must have demonstrated a significant percent drop in the confirmatory inhibition of binding assay to be considered positive. The inhibition of binding confirmatory assay was performed identically to the direct binding screening assay with the exception that the samples were tested in parallel with excess unlabeled raxibacumab.

As-treated population

Blood was collected from each participant at selected times post dose, and serum specimens were analyzed for raxibacumab using a validated electrochemiluminescense-based assay. The individual serum raxibacumab concentration data were summarized by nominal collection time and treatment group using descriptive statistics. Blood samples for serum raxibacumab concentration measurement were collected from participants who received a single-dose prior to administration of the raxibacumab and diphenhydramine doses on Day 0, at 30 minutes and 2 to 6 hours after completion of the raxibacumab infusion, and at 14, 28, and 56 days after the raxibacumab dose.

Pharmacokinetics (PK) Population: all evaluable participants who received a raxibacumab dose and had at least 1 measurable post-dose serum raxibacumab concentration.

Blood was collected from each participant at selected times post dose, and serum specimens were analyzed for raxibacumab using a validated electrochemiluminescense-based assay. The individual serum raxibacumab concentration data were summarized by nominal collection time and treatment group using descriptive statistics. For the participants that received two doses, blood samples for serum raxibacumab concentration measurement were collected from participants prior to administration of the raxibacumab and diphenhydramine doses on Days 0 and 14, at 30 minutes and 2 to 6 hours after completion of each raxibacumab infusion, and at 28, 42, 56, and 70 days after the 1st raxibacumab dose.

Pharmacokinetics (PK) Population: all evaluable participants who received a raxibacumab dose and had at least 1 measurable post-dose serum raxibacumab concentration.

Participants received a double dose of placebo administered 14 days apart via IV infusion. Participants were treated with oral diphenhydramine (25-50 mg) up to 60 minutes prior to infusion of placebo.

Participants received a single dose of 40 milligrams (mg)/kilogram (kg) raxibacumab administered via IV infusion. Participants were treated with oral diphenhydramine (25-50 mg) up to 60 minutes prior to infusion of raxibacumab.

Participants received a double dose of 40 mg/kg raxibacumab administered 14 days apart via IV infusion. Participants were treated with oral diphenhydramine (25-50 mg) up to 60 minutes prior to infusion of raxibacumab.