Rabies Immune Globulin Dosing in Adults
For an unvaccinated adult exposed to rabies, administer human rabies immune globulin (HRIG) at exactly 20 IU per kilogram of body weight on day 0, infiltrating the entire calculated dose around and into all wounds when anatomically feasible, with any remaining volume given intramuscularly at a site distant from the vaccine injection. 1, 2, 3
Dose Calculation and Administration
Calculate the total HRIG dose by multiplying the patient's weight in kilograms by 20 IU (e.g., an 80 kg adult requires 1,600 IU total). 1, 2
Administer HRIG on day 0, ideally at the same time as the first rabies vaccine dose, to provide immediate passive immunity while vaccine-induced antibodies develop over the subsequent 7–10 days. 1, 2
If HRIG is not given on day 0, it may still be administered up to and including day 7 after the first vaccine dose; beyond day 7, HRIG should not be given because vaccine-induced antibodies are presumed to have developed and additional passive antibody may suppress the active immune response. 1, 2
Critical Administration Technique
Infiltrate the entire calculated HRIG dose into and around every wound whenever anatomically feasible—this local infiltration is essential for neutralizing virus at the exposure site and has been linked to prophylaxis success. 1, 2
Inject any remaining HRIG volume intramuscularly at a site distant from the rabies vaccine injection site (e.g., if vaccine is given in the deltoid, administer remaining HRIG in the opposite deltoid or thigh). 1, 2
Never administer HRIG in the same syringe or at the same anatomical site as the rabies vaccine, as co-administration interferes with active antibody production. 1, 2, 3
Dosing Limits and Pitfalls
Do not exceed 20 IU/kg—higher doses have been shown to partially suppress the vaccine-induced antibody response and may compromise protection. 1, 2, 4
Failure to infiltrate wounds with the full calculated dose has been associated with rare post-exposure prophylaxis failures, underscoring the importance of complete wound infiltration rather than simply administering the entire dose intramuscularly. 2
Never use the gluteal area for HRIG administration—studies demonstrate that gluteal injection results in barely detectable circulating antibody levels, likely below protective thresholds. 5
Complete Post-Exposure Prophylaxis Regimen
Combine HRIG with a 4-dose rabies vaccine series (1.0 mL intramuscularly on days 0,3,7, and 14) administered in the deltoid muscle for adults. 1
Previously vaccinated adults require only 2 vaccine doses (days 0 and 3) and should never receive HRIG, as it will inhibit the anamnestic antibody response. 1, 2
Immunocompromised adults require a 5-dose vaccine regimen (days 0,3,7,14, and 28) plus HRIG at 20 IU/kg on day 0, even if previously vaccinated, with mandatory serologic testing 1–2 weeks after the final dose to confirm adequate antibody response. 1
Equine Rabies Immune Globulin Alternative
If human rabies immune globulin is unavailable, equine rabies immune globulin (ERIG) may be substituted at 40 IU/kg body weight—double the HRIG dose—because equine immunoglobulin has a shorter half-life and different pharmacokinetics. 6, 5
ERIG administration technique is identical to HRIG: infiltrate the entire calculated dose into and around wounds, with any remaining volume given intramuscularly distant from the vaccine site. 6