Usage
- Equine Rabies Immunoglobulin (ERIG) is prescribed for post-exposure prophylaxis of rabies in individuals suspected of exposure to the rabies virus. It is particularly crucial in cases of severe exposures, such as multiple bites, scratches, or contamination of mucous membranes with saliva from a rabid or suspected rabid animal. It is especially important for bites located on the face, head, neck, and hands, and for bites in young children.
- Pharmacological Classification: Passive immunizing agent, immunoglobulin.
- Mechanism of Action: ERIG provides immediate passive immunity by supplying rabies-specific antibodies that neutralize the rabies virus at the site of exposure before the individual’s immune system can mount its own response. It is crucial to administer ERIG in conjunction with the rabies vaccine to ensure both immediate and long-term protection. ERIG itself does not constitute complete anti-rabies treatment.
Alternate Names
- Equine Rabies Antiserum
- Rabies Antiserum I.P. - Equine
- Purified Equine Rabies Immunoglobulin F(ab’)2 Fragments
- Brand Names: Equirab, Rabix-IG, Favirab (contains F(ab’)2 fragments)
How It Works
- Pharmacodynamics: ERIG provides passive immunity by delivering preformed rabies-specific antibodies. These antibodies neutralize the rabies virus by binding to its surface antigens, preventing the virus from entering nerve cells and spreading to the central nervous system. This neutralization is crucial in the early stages of exposure before the virus reaches the brain.
- Pharmacokinetics: ERIG is administered intramuscularly (IM) or locally infiltrated around the wound. The F(ab’)2 fragments, when used, have a smaller molecular size and are more readily distributed to the tissues surrounding the wound. Intravenous (IV) administration is contraindicated. The antibodies are gradually eliminated from the body through normal physiological processes.
- Mode of Action/Receptor Binding/Enzyme Inhibition/Neurotransmitter Modulation: ERIG acts by directly binding to the rabies virus, specifically to the glycoprotein on the viral surface. This binding prevents viral entry into nerve cells, thus neutralizing the virus and interrupting the infectious process. No enzyme inhibition or neurotransmitter modulation is involved.
- Elimination Pathways: Elimination is primarily through protein catabolism.
Dosage
Standard Dosage
Adults: 40 IU/kg body weight, administered as a single dose.
Children: 40 IU/kg body weight, administered as a single dose. Pediatric safety considerations include the potential for hypersensitivity reactions, as with adults. For multiple wounds, particularly in children, the dose can be diluted in sterile normal saline to ensure adequate infiltration of all wound sites.
Special Cases:
- Elderly Patients: No specific dosage adjustments are typically required but administer with caution.
- Patients with Renal Impairment: No specific dosage adjustments are indicated.
- Patients with Hepatic Dysfunction: No specific dosage adjustments are indicated.
- Patients with Comorbid Conditions: While no explicit dosage adjustments are specified for these conditions, careful monitoring and supportive care are essential.
Clinical Use Cases
ERIG is specifically indicated for post-exposure rabies prophylaxis; it is not used in the clinical settings described (intubation, surgical procedures, mechanical ventilation, ICU use, emergency situations).
Dosage Adjustments
The maximum dose should not be exceeded, as this may interfere with the immune response to the rabies vaccine.
Side Effects
Common Side Effects
- Local reactions at the injection site (pain, swelling, redness, induration)
- Fever
- Headache
- Malaise
- Myalgia
- Arthralgia
Rare but Serious Side Effects
- Hypersensitivity reactions, including anaphylaxis (urticaria, dyspnea, hypotension)
- Serum sickness
Long-Term Effects
Generally, no long-term adverse effects are associated with ERIG, as it is a single dose treatment.
Adverse Drug Reactions (ADR)
Anaphylaxis is a significant ADR and requires immediate medical intervention.
Contraindications
- History of severe hypersensitivity to equine serum or any component of the product. While a skin test is sometimes performed, it is not a reliable predictor of allergic reactions.
Drug Interactions
- Rabies Vaccine: ERIG should be administered concurrently with the rabies vaccine, but at a different anatomical site. Do not mix in the same syringe. ERIG may partially suppress the active antibody response to the rabies vaccine. Do not administer repeat doses of ERIG once vaccination has been initiated.
- Live Attenuated Virus Vaccines: May interfere with the immune response to live vaccines, such as MMR, varicella, and rotavirus. These vaccines should be delayed for at least three months after ERIG administration.
- Immunosuppressants: Concomitant use with immunosuppressants may reduce the efficacy of the rabies vaccine. Closely monitor patients receiving both treatments.
Pregnancy and Breastfeeding
- Pregnancy Safety Category: While formal studies are lacking, pregnancy is not considered a contraindication to ERIG administration due to the seriousness of rabies. Human Rabies Immunoglobulin (HRIG) is preferred if available.
- Fetal Risks/Teratogenicity: No specific data available.
- Breastfeeding: It is unknown whether ERIG is excreted in breast milk. The risks and benefits should be carefully weighed for the mother and infant.
Drug Profile Summary
- Mechanism of Action: Provides passive immunity by neutralizing rabies virus with equine antibodies.
- Side Effects: Local reactions, fever, headache, hypersensitivity (rarely anaphylaxis).
- Contraindications: Hypersensitivity to equine serum.
- Drug Interactions: Rabies vaccine (administer concurrently but at a different site), live attenuated virus vaccines (delay administration).
- Pregnancy & Breastfeeding: Use with caution; HRIG preferred if available.
- Dosage: 40 IU/kg, single dose, IM or wound infiltration.
- Monitoring Parameters: Monitor for signs of allergic reactions (especially after administration).
Popular Combinations
ERIG is administered in combination with the rabies vaccine.
Precautions
- Screen for allergies to equine proteins. Have appropriate medical treatment readily available to manage potential hypersensitivity reactions, including anaphylaxis.
- Pregnant Women: Weigh the risk of rabies against potential risks to the fetus. HRIG is generally preferred if available.
- Breastfeeding Mothers: Weigh potential risks to the neonate.
- Children & Elderly: Standard dosing applies, but monitor closely.
FAQs (Frequently Asked Questions)
Q1: What is the recommended dosage for Equine Rabies Immunoglobulin?
A: The recommended dosage for both adults and children is 40 IU/kg body weight, administered as a single dose via IM injection or infiltrated around the wound.
Q2: Can ERIG be administered intravenously?
A: No, ERIG should never be administered intravenously. It should be administered IM or via local infiltration around the wound.
Q3: Is a skin test required before administering ERIG?
A: While a skin test may sometimes be performed, it is not a reliable predictor of allergic reactions. The WHO does not recommend routine skin testing before ERIG administration.
Q4: What is the difference between ERIG and HRIG?
A: ERIG is derived from horse serum, while HRIG is derived from human serum. HRIG is generally preferred due to its lower risk of side effects, but ERIG is a more readily available and cost-effective alternative.
Q5: Can ERIG be given to a pregnant woman?
A: Yes, considering the severity of rabies infection, pregnancy is not a contraindication to ERIG administration. However, HRIG is preferred if available.
Q6: What should be done if a patient experiences an allergic reaction to ERIG?
A: Immediately discontinue administration and provide appropriate medical treatment for allergic reactions or anaphylaxis, including epinephrine, antihistamines, and corticosteroids.
Q7: Can ERIG be used for pre-exposure prophylaxis?
A: No, ERIG is only used for post-exposure prophylaxis. Pre-exposure prophylaxis involves administering the rabies vaccine alone.
Q8: How long does the passive immunity conferred by ERIG last?
A: The passive immunity provided by ERIG is transient and typically lasts for a few weeks. This is why it’s crucial to administer the rabies vaccine alongside ERIG to provide long-lasting active immunity.
Q9: What first-aid measures should be taken after a potential rabies exposure?
A: Immediately and thoroughly wash the wound with soap and water for at least 15 minutes. This can significantly reduce the risk of rabies transmission. A virucidal agent like povidone-iodine can also be used if available.
