What is the correct dose of human rabies immune globulin (HRIG) based on a patient’s weight and how should it be administered?

Rabies Immune Globulin Dosing Calculation

The standard dose of human rabies immune globulin (HRIG) is 20 IU per kilogram of body weight, calculated by multiplying the patient's weight in kilograms by 20 IU, regardless of age. 1, 2, 3

Dose Calculation Formula

• Multiply the patient's body weight (kg) × 20 IU = total HRIG dose in international units 1, 2, 3
• This formula applies universally to all age groups, including infants, children, and adults 1, 2
• For example, an 80 kg patient requires 1,600 IU total dose 2

Administration Technique

• The entire calculated dose must be thoroughly infiltrated around and into all bite wounds whenever anatomically feasible 1, 2, 3
• Any remaining volume after wound infiltration should be administered intramuscularly at a site distant from the vaccine injection site 1, 2, 3
• Never administer HRIG in the same syringe or at the same anatomical site as the rabies vaccine, as this interferes with active antibody production 1, 2, 3

Critical Dosing Precautions

• Do not exceed 20 IU/kg body weight—higher doses partially suppress the vaccine-induced antibody response and may compromise protection 1, 2, 3
• The gluteal region should not be used for intramuscular injection of any remaining HRIG volume due to risk of sciatic nerve injury 3
• Administer remaining volume in the deltoid muscle of the upper arm or lateral thigh muscle instead 3

Timing of Administration

• HRIG should be given on day 0, ideally at the same time as the first rabies vaccine dose 1, 2, 3
• If not administered initially, HRIG can still be given up to and including day 7 after the first vaccine dose 1, 2, 3
• Beyond day 7, do not administer HRIG because vaccine-induced antibodies are presumed to have developed, and additional passive antibody may suppress the active immune response 1, 2

Common Implementation Errors

• A 2020 study found that while 98% of patients received the correct HRIG dose, only 56% received proper wound infiltration as recommended—this is a critical error that may reduce prophylactic effectiveness 2
• Failure to infiltrate wounds with the full calculated dose has been associated with rare failures of post-exposure prophylaxis 1, 2

Special Population Considerations

• Previously vaccinated persons should NOT receive HRIG—they require only vaccine doses on days 0 and 3, as HRIG will inhibit the anamnestic antibody response 1, 2, 4
• Immunocompromised patients require the full HRIG dose (20 IU/kg) plus a 5-dose vaccine regimen on days 0,3,7,14, and 28 2, 4