1. Clinical Overview
Equine Rabies Immunoglobulin (ERIG) is a sterile, concentrated, and purified solution of immunoglobulins derived from the plasma of horses hyperimmunized with rabies virus vaccine. It provides immediate, passive immunity against the rabies virus by neutralizing the virus at the site of exposure before it can enter the nervous system. It is a critical component of Category III rabies post-exposure prophylaxis (PEP) as per WHO and National Centre for Disease Control (NCDC), India guidelines. It is used in conjunction with rabies vaccine.
| Onset | Duration | Bioavailability |
|---|---|---|
| Immediate, with neutralizing antibodies detectable within hours of administration. | Approximately 7 to 14 days, providing a bridge until the patient's own active immunity from the rabies vaccine develops (around day 7). | 100% via intramuscular administration; not applicable for intravenous use as it is strictly for local infiltration and IM use. |
2. Mechanism of Action
ERIG contains high-titer, virus-neutralizing antibodies (IgG) against the rabies virus. When infiltrated around and into the wound(s), these antibodies bind to the rabies virus glycoprotein (G protein), preventing viral attachment and entry into peripheral nerve endings. This provides immediate, short-term passive immunity, neutralizing any virus present at the site of inoculation before it can travel centripetally along neural pathways to the central nervous system.
3. Indications & Uses
- Post-exposure prophylaxis (PEP) for Category III animal bite exposures (transdermal bites, licks on broken skin, contamination of mucous membrane with saliva) as per WHO/NCDC guidelines.
- PEP for all Category II exposures in immunocompromised individuals.
4. Dosage & Administration
Adult Dosage: 20 IU per kg body weight. For a 1000IU vial, calculate total required IU (20 x weight in kg). Infiltrate as much as possible anatomically feasible into and around the wound(s). Any remaining volume should be administered by deep intramuscular (IM) injection at a site distant from the vaccine administration site (e.g., anterolateral thigh or deltoid).
Administration: 1. Perform a skin test prior to administration (intradermal injection of 0.02ml of 1:100 dilution in normal saline; read after 15-30 minutes). 2. Use strict aseptic technique. 3. Clean wounds thoroughly with soap and water, povidone-iodine. 4. Infiltrate the full dose of RIG into and around all wounds. 5. If wounds are small or on fingers, dilute with normal saline to achieve sufficient volume for infiltration. 6. Do not administer intravenously. 7. Administer the first dose of rabies vaccine simultaneously but at a different anatomical site (e.g., opposite deltoid or anterolateral thigh).
5. Side Effects
Common side effects may include:
- Local: Pain, tenderness, and stiffness at the injection/infiltration site.
- Systemic: Low-grade fever, malaise, headache.
6. Drug Interactions
| Drug | Effect | Severity |
|---|---|---|
| Live Virus Vaccines (e.g., MMR, Varicella, Yellow Fever) | ERIG may interfere with the immune response to live vaccines. Administration of such vaccines should be deferred for at least 3 months after ERIG administration. | Moderate |
| Corticosteroids, Immunosuppressants (e.g., Azathioprine, Cyclosporine) | May theoretically reduce the efficacy of the concomitant active rabies vaccine. However, for rabies PEP, these drugs are not a contraindication; ensure full vaccine course is given. | Moderate |
| Other Immunoglobulins | Concurrent use may increase the risk of systemic adverse reactions. | Low |
7. Patient Counselling
- DO complete the entire course of rabies vaccine as scheduled, even if you receive the immunoglobulin.
- DO inform the doctor of any history of allergies, especially to horse serum or previous antiserum injections.
- DO report immediately any signs of difficulty breathing, swelling of face/lips, rash, or severe joint pain after the injection.
- DO NOT skip or delay the immunoglobulin if prescribed for a Category III bite.
- DO NOT apply any native/traditional medicines (e.g., chillies, herbs, soil) to the wound.
8. Toxicology & Storage
Overdose: Overdose is unlikely due to weight-based dosing. Theoretical risks include volume overload from large IM injections and increased incidence of serum sickness or hypersensitivity reactions.
Storage: Store between +2°C to +8°C (in a refrigerator). Do not freeze. Protect from light. The vial is for single use in one patient only. Do not use if the solution is cloudy or contains particulate matter. Do not shake vigorously. Use immediately after opening.