Anthim Side Effects Center

Last updated on RxList: 4/21/2020
Anthim Side Effects Center

Medical Editor: John P. Cunha, DO, FACOEP

What Is Anthim?

Anthim (obiltoxaximab) injection is a monoclonal antibody directed against the protective antigen of Bacillus anthracis indicated in adult and pediatric patients for treatment of inhalational anthrax due to B. anthracis in combination with appropriate antibacterial drugs and, for prophylaxis of inhalational anthrax when alternative therapies are not available or are not appropriate.

What Are Side Effects of Anthim?

Common side effects of Anthim include:

  • headache
  • itching
  • upper respiratory tract infection
  • cough
  • vessel puncture site bruise
  • infusion site pain or swelling
  • stuffy nose
  • hives, and
  • pain in extremities

Dosage for Anthim

The recommended dosage of Anthim is based on the patient's body weight.

What Drugs, Substances, or Supplements Interact with Anthim?

Anthim may interact with other drugs. Tell your doctor all medications and supplements you use.

Anthim During Pregnancy and Breastfeeding

Tell your doctor if you are pregnant before using Anthim. It is unknown if Anthim passes into breast milk. Consult your doctor before breastfeeding.

Additional Information

Our Anthim (obiltoxaximab) injection Side Effects Drug Center provides a comprehensive view of available drug information on the potential side effects when taking this medication.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.


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Anthim Professional Information


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

  • Hypersensitivity and Anaphylaxis [see WARNINGS AND PRECAUTIONS].

Clinical Trials Experience

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].

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

Adverse ReactionsPlacebo
N = 70 (%)
Single Dose ANTHIM
N = 300* (%)
Headache4 (6%)24 (8%)
Pruritus1 (1%)11 (4%)
Infections of the upper respiratory tract2 (3%)14 (5%)
Cough09 (3%)
Vessel puncture site bruise1 (1%)8 (3%)
Infusion site swelling1 (1%)8 (3%)
Nasal congestion1 (1%)5 (2%)
Infusion site pain07 (2%)
Urticaria05 (2%)
Pain in extremity1 (1%)5 (2%)
*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 important 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.

Read the entire FDA prescribing information for Anthim (Obiltoxaximab Intravenous Infusion)


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© Anthim Patient Information is supplied by Cerner Multum, Inc. and Anthim Consumer information is supplied by First Databank, Inc., used under license and subject to their respective copyrights.

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