ANTHIM Solution for injection Ref.[10346] Active ingredients: Obiltoxaximab

5.1 Hypersensitivity and Anaphylaxis

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.

The following clinically important adverse reactions are described elsewhere in the labeling:

• Hypersensitivity and Anaphylaxis [see Warnings and Precautions (5.1)]

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.

Adverse Reactions Leading to Discontinuation of ANTHIM Infusion

ANTHIM infusion was discontinued in 8/320 healthy subjects (2.5%) in clinical trials due to hypersensitivity reactions or anaphylaxis [see Warnings and Precautions (5.1)].

Most Frequently Reported Adverse Reactions

The most frequently reported adverse reactions 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.

Table 3 shows the adverse reactions that occurred in ≥1.5% of healthy subjects receiving a single dose of ANTHIM (16 mg/kg IV) and more frequently than those receiving placebo.

Table 3. Adverse Reactions Reported in ≥1.5% of Healthy Adult Subjects Exposed to a Single Dose of ANTHIM 16 mg/kg IV:

* Single-dose population: 210 subjects in study 1 plus 70 subjects in the first treatment period of study 2 plus 20 subjects in the ANTHIM alone treatment arm of study 3

Effect of Diphenhydramine on the Incidence of Adverse Reactions

Overall in the single-dose population, subjects who received pre-medication with diphenhydramine were less likely to experience adverse reactions with administration of ANTHIM compared to those who did not (42% vs. 58% respectively). Specifically, the incidence of the following adverse reactions was lower in the subjects who received diphenhydramine prior to ANTHIM infusion compared to those who did not: headache (5% vs. 16%), cough (1% vs. 8%), rash (2% vs. 7%), pruritus (3% vs. 4%) throat irritation (0 vs. 3%), rhinorrhea (0 vs. 3%), and infusion site erythema (0% vs. 4%). Somnolence was only reported in subjects who were pretreated with diphenhydramine.

Less Common Adverse Reactions

Clinically significant adverse reactions that were reported in <1.5% of subjects exposed to ANTHIM and at rates higher than in placebo subjects are listed below:

• General disorders and administration site conditions: chest discomfort/pain, fatigue, pyrexia, intravenous site discoloration
• Musculoskeletal and connective tissue disorders: myalgia, musculoskeletal pain
• Respiratory, thoracic and mediastinal disorders: oropharyngeal pain, sinus congestion, rhinorrhea, dysphonia, dyspnea
• Investigations: lymphocyte count decreased, neutrophil count decreased, white blood count decreased, increased creatine phosphokinase
• Cardiac disorders: palpitations, cyanosis
• Neurologic disorders: dizziness
• Gastrointestinal disorders: vomiting, dry mouth

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.

7.1 Ciprofloxacin

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)].

Risk Summary

There are no data on the use of ANTHIM in pregnant women to inform on drug-associated risk. There are adverse effects on maternal and fetal outcomes associated with anthrax in pregnancy (see Clinical Considerations). In pregnant rabbits, intravenous administration of obiltoxaximab during organogenesis was not associated with adverse developmental outcomes at up to 0.62 times the human systemic exposure at the maximum recommended adult dose (see Data).

The estimated background risk of major birth defects and miscarriage for the indicated population is unknown. All pregnancies have a background risk of birth defect, loss, or other adverse outcomes. In the U.S. general population, the estimated background risk of major birth defects and miscarriage in clinically recognized pregnancies is 2% to 4% and 15% to 20%, respectively.

Clinical Considerations

Disease-Associated Maternal and/or Embryo/Fetal Risk

Limited data in the form of case reports of anthrax infection in pregnant women indicate that maternal infection is associated with a high risk of maternal, fetal, and neonatal deaths, particularly in the absence of treatment.

Data

Animal Data

A study was conducted in pregnant, healthy, New Zealand White rabbits administered intravenous obiltoxaximab at dose levels of 16 or 32 mg/kg during organogenesis on Gestation Days 6, 10, 13 and 17. No maternal toxicity or adverse developmental outcomes were observed at the highest tested dose, 32 mg/kg. In those rabbits, mean maternal maximum plasma concentration (C_max = 1180 mcg/mL) and mean maternal AUC_inf (3220 mcg•day/mL) were approximately 3 times and 0.62 times the respective values for C_max and AUC reported in clinical trial subjects at the maximum recommended adult dose of 16 mg/kg.

Risk Summary

There is no information available on the presence of obiltoxaximab in human milk, the effects on the breastfed child, or the effects on milk production. Maternal IgG is known to be present in human milk. Therefore, the development and health benefits of breastfeeding should be considered along with the mother’s clinical need for ANTHIM and any potential adverse effects on the breastfed child from ANTHIM or from the underlying maternal condition.

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)].