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.
The efficacy of ANTHIM for treatment and prophylaxis of inhalational anthrax was studied in multiple studies in the cynomolgus macaques 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.
The animals were challenged with aerosolized Bacillus anthracis spores (Ames strain) at approximately 200xLD50 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.
Two studies in NZW rabbit and two studies in cynomolgus macaques 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 in both species. Survival rates were 93% and 62% with ANTHIM compared to 0 or 0 placebo survivors in rabbits and 47% and 31-35% survival with ANTHIM compared to 6% or 0% placebo survival in macaques (see table below).
|Proportion of Survival at Day 28a (# survived/n)||p-valueb||95% CIc|
|Placebo||ANTHIM 16 mg/kg IV|
|Study 1||0 (0/9)||93% (13/14)||0.0010||(0.59, 1.00)|
|Study 2||0 (0/13)||62% (8/13)||0.0013||(0.29, 0.86)|
|Study 3||6 % (1/16)||47% (7/15)||0.0068||(0.09, 0.68)|
|Study 4d||0 (0/17)||31% (5/16)
IV: intravenous, CI: Confidence Interval
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 (see figure below).1
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.1 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 (see table below). 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).
|Treatment Time (hrs)||Number (%) Survivala||p-valueb||95% CIc|
|ANTHIM 16 mg/kg||18||6/6
|ANTHIM 16 mg/kg||24||5/6
|ANTHIM 16 mg/kg||36||3/6
CI: Confidence Interval
ANTHIM® (obiltoxaximab) 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 are not appropriate.
WARNING: HYPERSENSITIVITY and ANAPHYLAXIS
Hypersensitivity and anaphylaxis have been reported during the intravenous infusion of ANTHIM. Due to the risk of hypersensitivity and anaphylaxis, ANTHIM should be administered in monitored settings by personnel trained and equipped to manage anaphylaxis. Monitor individuals who receive ANTHIM closely for signs and symptoms of hypersensitivity reactions throughout the infusion and for a period of time after administration. Stop ANTHIM infusion immediately and treat appropriately if hypersensitivity or anaphylaxis occurs.
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.
Premedication with diphenhydramine is recommended prior to administration of ANTHIM. Diphenhydramine premedication does not prevent anaphylaxis, and may mask or delay onset of symptoms of hypersensitivity.
The safety of ANTHIM has been studied only in healthy volunteers. It has not been studied in patients with inhalational anthrax. The most frequently reported adverse reactions (occurred in >1.5% of healthy subjects) were headache, pruritus, infections of the upper respiratory tract, cough, vessel puncture site bruise, infusion site swelling, urticaria, nasal congestion, infusion site pain, and pain in extremity.
No adequate and well-controlled studies in pregnant women were conducted. Because animal reproduction studies are not always predictive of human response, ANTHIM should be used during pregnancy only if clearly needed.
There have been no studies of the safety or PK of ANTHIM in the pediatric population.