Can equine rabies immune globulin (ERIG) be administered intramuscularly, and what is the recommended dose?

ERIG Administration and Dosing

Yes, equine rabies immune globulin (ERIG) can be administered intramuscularly, but only for the portion that cannot be infiltrated into the wound—the recommended dose is 40 IU/kg body weight, with as much as anatomically feasible infiltrated around and into the wound, and any remaining volume given IM at a site distant from vaccine administration. 122

Dosing Algorithm

Calculate Total ERIG Dose

• 40 IU/kg body weight for equine RIG (ERIG)
• For comparison: Human RIG (HRIG) is 20 IU/kg 13
• This formula applies to all ages, including infants and children 12

Administration Priority (Critical)

Step 1: Wound Infiltration First

• Infiltrate as much of the calculated dose as anatomically feasible directly into and around all wounds 122
• This is the most important step—failures of post-exposure prophylaxis have been reported when inadequate RIG was infiltrated at exposure sites 14

Step 2: Remaining Volume IM

• Any remaining volume that could not be infiltrated should be given IM at a site distant from vaccine administration 122
• Never administer in the same syringe or same anatomical site as the rabies vaccine 12

Critical Timing and Caveats

When to Give ERIG

• Administer on Day 0 (same day as first vaccine dose) 12
• Can be given up to and including Day 7 if not given initially 12
• Do NOT give after Day 7—antibody response to vaccine is presumed to have occurred by then 12

Common Pitfalls to Avoid

Never exceed the recommended dose (40 IU/kg for ERIG)—excess immunoglobulin can partially suppress active antibody production from the vaccine 12

Avoid the outdated 50:50 method—older guidelines recommended giving half at the wound and half elsewhere, but current WHO and ACIP guidelines emphasize infiltrating as much as possible into wounds, with only the remainder given IM 4. The outdated method has been associated with treatment failures 4.

Do not give ERIG to previously vaccinated persons—it may blunt their rapid memory response to rabies antigen 22. Previously immunized individuals need only 2 vaccine doses (Days 0 and 3) without any immunoglobulin 12.

Site Selection for IM Portion

• The gluteal area should be avoided for vaccine injections (associated with lower antibody titers) 15
• For the IM portion of ERIG that cannot be infiltrated into wounds, use a site distant from vaccine administration 12

Safety Considerations

• Skin testing is mentioned in some protocols 6, though serious systemic reactions are uncommon
• Serum sickness-like reactions can occur around Day 8, presenting with rash, fever, and arthralgias 7
• Local reactions (pain, induration) at injection sites are common but generally mild 86