📋 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.

💊 Dosage & Administration

Adult: 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).

Note: 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).

⚠️ Contraindications

History of severe systemic hypersensitivity reaction (e.g., anaphylaxis) to equine proteins or previous administration of ERIG.
Administration after 7 days of initiation of the rabies vaccine series.

🔬 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.

🤕 Side Effects

Local: Pain, tenderness, and stiffness at the injection/infiltration site.
Systemic: Low-grade fever, malaise, headache.

🤰 Special Populations

Pregnancy: Pregnancy Category C. No well-controlled studies. However, rabies PEP is NOT contraindicated and is considered LIFE-SAVING for both mother and fetus. The risk of rabies far outweighs any theoretical risk from ERIG.

Driving: May cause dizziness, malaise, or fever. Patients should be cautioned about driving or operating machinery if they experience such effects.

🔄 Drug Interactions

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

Rabiig