Usage
Diphtheria Immune Globulin (also known as diphtheria antitoxin) is a medication prescribed for the treatment of respiratory and cutaneous diphtheria caused by toxigenic Corynebacterium diphtheriae, C. ulcerans, or C. pseudotuberculosis. Its pharmacological classification is as an immunizing agent, specifically an antitoxin. It works by neutralizing the diphtheria toxin circulating in the bloodstream, preventing it from binding to host cells. This neutralization halts the progression of the disease and reduces further damage caused by the toxin. It does not eradicate the bacteria themselves; antibiotic treatment is required for that purpose.
Alternate Names
Diphtheria antitoxin, DAT. Note that this should not be confused with Diphtheria-Tetanus toxoid, which is a vaccine for preventing diphtheria, rather than treating an active infection. This medication is no longer licensed by the FDA in the United States.
How It Works
Pharmacodynamics: Diphtheria Immune Globulin contains antibodies specific to the diphtheria toxin. Intravenously administered, it binds to and neutralizes circulating toxin, preventing it from attaching to cell receptors and entering cells. This halts the toxin’s damaging effects, which include inhibiting protein synthesis and causing tissue damage in the respiratory system, heart, and nervous system. The antitoxin does not reverse damage already caused by the toxin.
Pharmacokinetics: Diphtheria Immune Globulin is administered intravenously for optimal efficacy, especially in severe cases. Intramuscular administration may be used in milder cases or when intravenous access is challenging. The product is typically diluted in normal saline before infusion. It distributes throughout the extracellular fluid compartment. Elimination occurs through normal immunoglobulin catabolism, which primarily involves proteolysis in various tissues and cells. The half-life of immunoglobulins can vary, typically around 21 days.
Mode of Action: Diphtheria toxin is composed of two subunits, A and B. Subunit B facilitates the toxin’s entry into cells, while subunit A inhibits protein synthesis within the cell. The antibodies in Diphtheria Immune Globulin bind specifically to subunit B, blocking the toxin from binding to host cell receptors and preventing cellular entry.
Dosage
Standard Dosage
Diphtheria antitoxin dosage is determined by disease severity and duration, not by patient age or weight. The dosage is the same for both adults and children.
- Mild Cases (Skin lesions only, or early respiratory infection <48 hours duration): 20,000 - 40,000 IU
- Moderate Cases (Respiratory infection <48 hours duration with some systemic symptoms): 40,000 - 60,000 IU
- Severe Cases (Extensive membrane formation, severe edema (“bull neck”), or respiratory infection >48 hours duration): 60,000 - 100,000 IU
Clinical Use Cases
The dosage recommendations remain consistent across various clinical settings, based on the severity and duration of the diphtheria infection, as described above.
Dosage Adjustments
Dosage is not adjusted based on renal or hepatic impairment, or other comorbid conditions. However, individuals with a history of allergies to equine proteins (horse allergy) or prior exposure to equine-derived products require sensitivity testing before administration and may require desensitization if a sensitivity is detected.
Side Effects
Common Side Effects
Pain, swelling, and redness at the injection site are common. Mild fever and malaise can also occur.
Rare but Serious Side Effects
Serum sickness (a delayed hypersensitivity reaction) can occur 7-10 days after administration, manifesting as fever, rash, joint pain, and swollen lymph nodes. Anaphylaxis (a severe, potentially life-threatening allergic reaction) is rare but possible, especially in individuals with a history of horse allergy or prior exposure to equine products.
Contraindications
- Known hypersensitivity to diphtheria antitoxin or any of its components. However, treatment should not be withheld if diphtheria is strongly suspected or confirmed, even with allergy history. Sensitivity testing and desensitization should be employed if necessary.
Drug Interactions
Live virus vaccines should be deferred for approximately three months after Diphtheria Immune Globulin administration, as the antibodies may interfere with the immune response to the vaccines.
Pregnancy and Breastfeeding
Diphtheria Immune Globulin can be used during pregnancy and breastfeeding if clinically indicated. The benefits of treating a life-threatening infection generally outweigh any potential risks. No specific adverse effects on the fetus or neonate have been reported.
Drug Profile Summary
- Mechanism of Action: Neutralizes circulating diphtheria toxin, preventing further cell damage.
- Side Effects: Injection site reactions, fever, malaise, serum sickness, rare anaphylaxis.
- Contraindications: Hypersensitivity (requiring sensitivity testing and potential desensitization).
- Drug Interactions: Live virus vaccines.
- Pregnancy & Breastfeeding: Can be used if indicated.
- Dosage: See detailed section above; depends on disease severity and duration.
- Monitoring Parameters: Vital signs (especially blood pressure and respiratory rate), signs of allergic reaction (rash, itching, difficulty breathing), symptoms of serum sickness.
Precautions
Sensitivity testing is required for individuals with horse allergies or prior exposure to equine products. Emergency medications for managing allergic reactions must be readily available during administration. Close monitoring for signs of anaphylaxis and serum sickness is crucial.
FAQs (Frequently Asked Questions)
Q1: What is the recommended dosage for Diphtheria Immune Globulin?
A: The dosage is determined by disease severity and duration, ranging from 20,000 to 100,000 IU. See dosage section for details. It is the same for adults and children.
Q2: How is Diphtheria Immune Globulin administered?
A: Intravenous administration is preferred, especially in severe cases. Intramuscular administration is an option for milder cases.
Q3: How does Diphtheria Immune Globulin differ from the diphtheria toxoid vaccine?
A: Diphtheria Immune Globulin treats active diphtheria infections, while the toxoid vaccine prevents diphtheria. They are not interchangeable.
Q4: What are the most serious potential side effects of Diphtheria Immune Globulin?
A: Anaphylaxis and serum sickness are rare but potentially severe side effects.
Q5: Can Diphtheria Immune Globulin be used in pregnant or breastfeeding women?
A: Yes, it can be used if the benefits outweigh the risks.
Q6: How quickly should Diphtheria Immune Globulin be administered after a diphtheria diagnosis?
A: As soon as possible. Early administration is crucial for maximizing effectiveness.
Q7: What other treatments are necessary for diphtheria in addition to Diphtheria Immune Globulin?
A: Antibiotics are necessary to eradicate the bacteria causing the infection. Supportive care may also be needed, depending on the severity of the illness.
Q8: Is sensitivity testing always necessary before administering Diphtheria Immune Globulin?
A: It is essential for patients with known horse allergies or prior exposure to equine-derived products. It’s also advisable to have emergency medications readily available for all patients receiving DAT in case of unexpected reactions.
Q9: What is the role of sensitivity testing prior to DAT administration?
A: Sensitivity testing identifies individuals potentially at risk for allergic reactions. A small amount of DAT is injected intradermally. If a wheal and flare reaction occurs, it indicates hypersensitivity, necessitating a desensitization protocol prior to full-dose administration.
Q10: Does a negative sensitivity test guarantee no allergic reaction?
A: No. While sensitivity testing can predict a high risk of allergic reaction to DAT in certain patients, a negative result doesn’t exclude the possibility of such reactions during DAT administration. Close observation for any signs of allergy throughout and after DAT administration is crucial.
