1. Clinical Overview
Equine Rabies Immunoglobulin (ERIG) is a sterile, purified, and concentrated solution of immunoglobulins derived from the plasma of horses hyperimmunized with rabies virus vaccine. It provides immediate, passive immunity against the rabies virus following a Category III exposure (transdermal bites, licks on broken skin, contamination of mucous membrane with saliva) as per WHO and National Rabies Control Programme (NRCP) guidelines. It is a critical component of Post-Exposure Prophylaxis (PEP) and must be administered as soon as possible after exposure, infiltrated around and into the wound(s), with the remainder given intramuscularly at a site distant from the rabies vaccine administration.
| Onset | Duration | Bioavailability |
|---|---|---|
| Immediate, within hours of administration. | Approximately 21-28 days (provides temporary passive immunity to bridge the gap until the active immunity from the rabies vaccine develops). | 100% when administered via intramuscular or local infiltration routes (systemic bioavailability). |
2. Mechanism of Action
ERIG contains high-titer neutralizing antibodies (IgG) against the rabies virus. Upon administration, these antibodies bind to the rabies virus glycoprotein antigens, neutralizing the virus and preventing its attachment and entry into susceptible host cells (primarily neurons). This provides immediate, short-term passive immunity, which is crucial during the initial period before the patient's own active immune response is generated by the concurrently administered rabies vaccine.
3. Indications & Uses
- Post-Exposure Prophylaxis (PEP) for Category III animal bite exposures to rabies (as per WHO/NRCP guidelines).
- PEP for Category II exposures in immunocompromised individuals or when the biting animal is confirmed rabid.
4. Dosage & Administration
Adult Dosage: 20 IU per kg body weight. For a 300IU vial, calculate total required dose (e.g., 15 kg patient requires 300IU). The entire calculated dose should be administered. As much as anatomically feasible is infiltrated into and around the wound(s). Any remaining volume is administered by deep intramuscular injection at a site distant from the rabies vaccine site (e.g., anterolateral thigh or deltoid).
Administration: 1. Calculate dose (20 IU/kg). 2. Perform skin sensitivity test if recommended by manufacturer/guidelines. 3. Clean wound thoroughly with soap and water, povidone-iodine. 4. Infiltrate as much of the dose as possible into and around all wound(s). Use a fine needle. 5. If volume is large or for multiple wounds, divide dose to infiltrate all sites. 6. Any leftover immunoglobulin is given IM in the anterolateral thigh (preferred) or deltoid, opposite the limb where vaccine is given. 7. NEVER administer in the same syringe or at the same site as the rabies vaccine. 8. Administer at the same time as the first dose of rabies vaccine (Day 0), but always after wound cleansing.
5. Side Effects
Common side effects may include:
- Pain, tenderness, and stiffness at the injection site.
- Low-grade fever.
- Mild local inflammatory reaction at wound infiltration site.
6. Drug Interactions
| Drug | Effect | Severity |
|---|---|---|
| Live Virus Vaccines (e.g., MMR, Varicella) | ERIG may interfere with the immune response to live virus vaccines. Administration of such vaccines should be deferred for at least 3 months after ERIG administration. | Moderate |
| Immunosuppressants (e.g., Corticosteroids, Chemotherapy) | May theoretically reduce the efficacy of the concurrent active rabies vaccination. However, rabies PEP is never withheld. Use standard PEP schedule. | Moderate |
| Other Immunoglobulins | May increase the risk of systemic adverse reactions. Not typically co-administered. | Low |
7. Patient Counselling
- DO complete the full course of rabies vaccine as scheduled (on Days 0, 3, 7, and 14/28).
- DO inform the doctor immediately if you experience rash, joint pain, fever, or difficulty breathing after the injection.
- DO continue thorough wound care with soap and water and antiseptic.
- DO inform all healthcare providers in the future that you have received equine-derived immunoglobulin.
- DONT skip or delay any dose of the rabies vaccine.
- DONT apply irritants like chili powder, soil, or herbs to the wound.
8. Toxicology & Storage
Overdose: Unlikely due to weight-based dosing. Theoretical risks include increased incidence of serum sickness, hyperviscosity syndrome (with extremely large doses), and arthralgia.
Storage: Store between +2°C to +8°C (in a refrigerator). Do not freeze. Protect from light. The vial is for single use only. Do not use if the solution is cloudy or contains particles. After withdrawal, use immediately. Do not shake vigorously.