Get your patient on Anthim (Obiltoxaximab)

ANTHIM is indicated in adult and pediatric patients for the treatment of inhalational anthrax due to Bacillus anthracis in combination with appropriate antibacterial drugs.

ANTHIM is indicated for prophylaxis of inhalational anthrax due to B. anthracis when alternative therapies are not available or not appropriate [see Indications and Usage (1.2 )] .

ANTHIM should only be used for prophylaxis when its benefit for prevention of inhalational anthrax outweighs the risk of hypersensitivity and anaphylaxis [see Warnings and Precautions (5.1 )] .

The effectiveness of ANTHIM is based solely on efficacy studies in animal models of inhalational anthrax. It is not ethical or feasible to conduct controlled clinical trials with intentional exposure of humans to anthrax [see Clinical Studies (14 )] .

Safety and PK of ANTHIM have been studied in adult healthy volunteers. There have been no studies of safety or PK of ANTHIM in the pediatric population. A population PK approach was used to derive intravenous infusion dosing regimens that are predicted to provide pediatric patients with exposure comparable to the observed exposure in adults [see Use in Specific Populations (8.4 )] .

ANTHIM binds to the protective antigen (PA) component of B. anthracis toxin; it does not have direct antibacterial activity. ANTHIM is not expected to cross the blood-brain barrier and does not prevent or treat meningitis. ANTHIM should be used in combination with appropriate antibacterial drugs.

• Pre-medicate with diphenhydramine prior to administering ANTHIM [see Warnings and Precautions (5.1 )] .
• Dilute the injection in 0.9% Sodium Chloride Injection, USP, before administering as an intravenous infusion [see Dosage and Administration (2.3 )] .
• The recommended dosage of ANTHIM in adult patients is a single dose of 16 mg/kg administered intravenously over 90 minutes (1 hour and 30 minutes) [see Dosage and Administration (2.4 )] .
• For adult patients weighing less than 40 kg, see Table 1 below.

• Pre-medicate with diphenhydramine prior to administering ANTHIM [see Warnings and Precautions (5.1 )].
• Dilute the injection in 0.9% Sodium Chloride Injection, USP, before administering as an intravenous infusion [see Dosage and Administration (2.3 )].
• The recommended dose for pediatric patients is based on weight as shown in Table 1 below.

• Administer the recommended dose of ANTHIM intravenously over 90 minutes (1 hour and 30 minutes) [see Dosage and Administration (2.4 )] .

There have been no studies of the safety or PK of ANTHIM conducted in the pediatric population. The dosing recommendations in Table 1 are derived from simulations using a population PK approach designed to match the observed adult exposure to ANTHIM at a 16 mg/kg dose [see Use in Specific Populations (8.4 )] .

Important Preparation Instructions

• Keep vials in their cartons prior to preparation of an infusion solution to protect ANTHIM from light. ANTHIM vials contain no preservative.
• Parenteral drug products should be inspected visually for particulate matter and discoloration prior to administration, whenever solution and container permit.
• Discard the vial if the solution is discolored or contains extraneous particles other than a few translucent-to- white, proteinaceous particles [see Description (11 )] .
• Do not shake the vial.

Preparation and Dilution in Bag for Infusion

1. Calculate the milligrams of ANTHIM injection needed by multiplying the recommended mg/kg dose in Table 2 by the patient weight in kilograms.
2. Calculate the required volume in milliliters of ANTHIM injection and number of vials needed for the dose by dividing the calculated dose in milligrams (step 1) by the concentration, 100 mg/mL. Each single vial allows delivery of 6 mL of ANTHIM.
3. Select an appropriate size bag of 0.9% Sodium Chloride Injection, USP. Withdraw a volume of solution from the bag equal to the calculated volume in milliliters of ANTHIM in step 2 above. Discard the solution that was withdrawn from the bag.
4. Withdraw the required volume of ANTHIM injection (calculated from step 2) from the ANTHIM vial(s). Discard any unused portion remaining in the ANTHIM vial(s).
5. Transfer the required volume of ANTHIM injection to the selected infusion bag.
6. Gently invert the bag to mix the solution. Do not shake.
7. The prepared solution is stable for 8 hours stored at room temperature 20°C to 25°C (68°F to 77°F) or 8 hours stored in the refrigerator at 2°C to 8°C (36°F to 46°F).

Preparation and Dilution in Syringe for Infusion

• Calculate lunused product.

• Administer ANTHIM in appropriately monitored settings which are equipped to manage anaphylaxis [see Warnings and Precautions (5.1 )] .
• Dilute ANTHIM injection [see Dosage and Administration (2.3 )] before administering ANTHIM intravenously using the bag or syringe for infusion.
• After preparation of the bag or syringe for infusion administer the infusion solution using a 0.22 micron inline filter with the infusion rate described in Table 2 [see Dosage and Administration (2.3 )] .
• Administer diluted ANTHIM intravenous infusion over 1 hour and 30 minutes. Monitor patients closely for signs and symptoms of hypersensitivity throughout the infusion and for a period of time after administration [see Warnings and Precautions (5.1 )] .
• Stop the infusion immediately and treat appropriately, if hypersensitivity or anaphylaxis occurs [see Warnings and Precautions (5.1 )] .
• Flush the line with 0.9% Sodium Chloride Injection, USP at the end of the intravenous infusion.

As in adults, the effectiveness of ANTHIM in pediatric patients is based solely on efficacy studies in animal models of inhalational anthrax. As exposure of healthy children to ANTHIM is not ethical, a population PK approach was used to derive intravenous dosing regimens that are predicted to provide pediatric patients with exposure comparable to the observed exposure in adults receiving 16 mg/kg. The dose for pediatric patients is based on weight [see Dosage and Administration (2.2 )] .

There have been no studies of safety or PK of ANTHIM in the pediatric population.

Clinical studies of ANTHIM did not include sufficient numbers of subjects aged 65 years and over to determine whether they respond differently from younger subjects. Of the 320 subjects in clinical studies of ANTHIM, 9.4% (30/320) were 65 years and over, while 2% (6/320) were 75 years and over. No alteration of dosing is needed for patients ≥65 years of age [see Clinical Pharmacology (12.3 )] .

Hypersensitivity reactions were the most common adverse reactions in the safety trials of ANTHIM, occurring in 34/320 healthy subjects (10.6%). Three (0.9%) cases of anaphylaxis occurred during or immediately after the infusion. In clinical trials, manifestations of anaphylaxis were rash/urticaria, cough, dyspnea, cyanosis, postural dizziness and chest discomfort. ANTHIM infusion was discontinued in 8 (2.5%) subjects due to hypersensitivity or anaphylaxis. The adverse reactions reported in these 8 subjects included urticaria, rash, cough, pruritus, dizziness, throat irritation, dysphonia, dyspnea and chest discomfort. The remaining subjects with hypersensitivity had predominantly skin-related symptoms such as pruritus and rash, and 6 subjects reported cough [see Adverse Reactions 6.1 ].

Due to the risk of anaphylaxis, ANTHIM should be administered in monitored settings by personnel trained and equipped to manage anaphylaxis. Patients should be monitored closely throughout the infusion period and for a period of time after administration [see Patient Counseling Information (17 )]. If anaphylaxis or hypersensitivity reactions occur, stop the infusion immediately and treat appropriately.

Premedication with diphenhydramine is recommended prior to administration of ANTHIM [see Dosage and Administration (2.1 ) and Adverse Reactions (6.1 )] . Diphenhydramine premedication does not prevent anaphylaxis, and may mask or delay onset of symptoms of hypersensitivity.

Because clinical trials are conducted under widely varying conditions, adverse reaction rates observed in the clinical trials of a drug cannot be directly compared to rates in the clinical trials of another drug and may not reflect the rates observed in practice. The safety of ANTHIM has been studied only in healthy volunteers. It has not been studied in patients with inhalational anthrax.

The safety of ANTHIM was evaluated in 320 healthy subjects treated with one or more 16 mg/kg IV doses in three clinical studies. Study 1 was a placebo-controlled study evaluating a single dose of ANTHIM vs. placebo (210 subjects received ANTHIM, 70 received placebo). Study 2 was a repeat-dose study in which 70 subjects received the first dose, but 34 and 31 subjects received a second dose of ANTHIM in sequences A (2 weeks apart) and B (≥ 4 months apart), respectively. Study 3 was a drug interaction study of a single dose of ANTHIM with ciprofloxacin in 40 subjects (20 subjects received ANTHIM alone and 20 subjects received ANTHIM plus ciprofloxacin for 9 days).

Subjects were 18 to 79 years of age, 54% were male, 70% Caucasian, 26% Black/African American, 2% American Indian/Alaska Native, 1% Asian and 10% Hispanic.

As with all therapeutic proteins, there is a potential for immunogenicity. The development of anti-ANTHIM antibodies was evaluated in all subjects receiving single and double doses of ANTHIM in studies 1, 2 and 3. Eight subjects (2.5%) who received at least one dose of IV ANTHIM were positive for a treatment-emergent anti-therapeutic antibody (ATA) response. Quantitative titers were low ranging from 1:20 – 1:320. There was no evidence of altered PK or toxicity profile in subjects with ATA development.

The incidence of antibody formation is highly dependent on the sensitivity and specificity of the immunogenicity assay. Additionally, the observed incidence of any antibody positivity in an assay is highly dependent on several factors, including assay sensitivity and specificity, assay methodology, sample handling, timing of sample collection, concomitant medications, and underlying disease. For these reasons, comparison of incidence of antibodies to obiltoxaximab with the incidence of antibodies to other products may be misleading.

Co-administration of 16 mg/kg ANTHIM intravenously with intravenous or oral ciprofloxacin in human subjects did not alter the PK of either ciprofloxacin or obiltoxaximab [see Clinical Pharmacology (12.3 )] .

Obiltoxaximab is a monoclonal antibody that binds the PA of B. anthracis [see Microbiology (12.4 )] .

The PK of obiltoxaximab are linear over the dose range of 4 mg/kg (0.25 times the lowest recommended dose) to 16 mg/kg following single IV administration in healthy subjects. Following single IV administration of ANTHIM 16 mg/kg in healthy, male and female human subjects, the mean C _max and AUC _inf were 400 ± 91.2 mcg/mL and 5170 ± 1360 mcg•day/mL, respectively.

Carcinogenicity, genotoxicity, and fertility studies have not been conducted with obiltoxaximab.

Central nervous system (CNS) lesions (bacteria, inflammation, hemorrhage and occasionally necrosis) were seen in anthrax-infected non-surviving NZW rabbits and cynomolgus macaques administered IV obiltoxaximab (≥4 mg/kg) or control at the time of disease confirmation. Microscopic changes in the non-surviving animals that received obiltoxaximab were due to the presence of extravascular bacteria and not the effect of obiltoxaximab. No dose response relationship for brain histopathology was identified. No treatment-related brain lesions were shown in anthrax-infected surviving NZW rabbits (at day 28) or cynomolgus macaques (up to day 56) after a single administration of obiltoxaximab at doses up to 16 mg/kg and up to 32 mg/kg/dose, respectively. No obiltoxaximab-related neurobehavioral effects were observed in surviving anthrax-infected cynomolgus macaques following treatment with obiltoxaximab.

Overview

Because it is not feasible or ethical to conduct controlled clinical trials in humans with inhalational anthrax, the efficacy of ANTHIM for the treatment of inhalational anthrax is based on efficacy studies in NZW rabbits and cynomolgus macaques. The animal efficacy studies are conducted under widely varying conditions, such that the survival rates observed in the animal studies cannot be directly compared between studies and may not reflect the rates observed in clinical practice.

Types of Studies

The efficacy of ANTHIM for treatment and prophylaxis of inhalational anthrax was studied in multiple studies in the cynomolgus macaque and NZW rabbit models of inhalational anthrax. These studies tested the efficacy of ANTHIM compared to placebo and the efficacy of ANTHIM in combination with antibacterial drugs relative to the antibacterial drugs alone.

Study Design

The animals were challenged with aerosolized B. anthracis spores (Ames strain) at approximately 200xLD ₅₀ to achieve 100% mortality if untreated. In prophylaxis studies of inhalational anthrax, animals were treated prior to the development of symptoms. In treatment studies, animals were administered treatment after exhibiting clinical signs or symptoms of systemic anthrax. Cynomolgus macaques were treated at the time of a positive serum electrochemiluminescence (ECL) assay for B. anthracis PA at a mean time of approximately 40 hours post-challenge with B. anthracis . In NZW rabbit treatment studies, animals were treated after a positive ECL assay for PA or sustained elevation of body temperature above baseline, at a mean time of approximately 30 hours post-challenge; the majority of animals triggered by temperature. In some of the treatment studies assessing the effect of ANTHIM in combination with antibacterial drugs, treatment was delayed to 72 to 96 hours post-challenge. Most study animals were bacteremic and had a positive ECL assay for PA prior to treatment. Survival was assessed at 28 days post-challenge with B. anthracis in most studies.

Results

NZW rabbit studies 1 and 2 and cynomolgus macaque studies 3 and 4 evaluated treatment with ANTHIM 16 mg/kg IV single dose compared to placebo in animals with systemic anthrax. Treatment with ANTHIM alone resulted in statistically significant improvement in survival relative to placebo (Table 4 ).

ANTHIM administered in combination with antibacterial drugs (levofloxacin, ciprofloxacin and doxycycline) for the treatment of systemic inhalational anthrax disease resulted in higher survival outcomes than antibacterial therapy alone in multiple studies where ANTHIM and antibacterial therapy was given at various doses and treatment times.

ANTHIM administered as prophylaxis resulted in higher survival outcomes compared to placebo in multiple studies where treatment was given at various doses and treatment times. In one study, cynomolgus macaques were administered ANTHIM 16 mg/kg at 18 hours, 24 hours or 36 hours after exposure. Survival was 6/6 (100%) at 18 hours, 5/6 (83%) at 24 hours, and 3/6 (50%) at 36 hours. Another cynomolgus macaque study evaluated ANTHIM 16 mg/kg administered 72, 48 or 24 hours prior to exposure. Survival was 100% at all three time points (14/14, 14/14, 15/15, respectively) at day 56 (end of study).