What is the appropriate dose and route of administration of human rabies immune globulin for a patient with a potentially rabid dog bite when the dog's rabies status is unknown?

Human Rabies Immune Globulin Dosing and Administration for Dog Bite

For a potentially rabid dog bite when the dog's rabies status is unknown, administer human rabies immune globulin (HRIG) at exactly 20 IU/kg body weight on day 0, infiltrating the full calculated dose around and into all bite wounds whenever anatomically feasible, with any remaining volume injected intramuscularly at a site distant from the rabies vaccine injection. 1, 2

Dose Calculation

• Calculate the total HRIG dose using the formula: patient's weight (kg) × 20 IU/kg = total IU required 1, 3
• This 20 IU/kg dose is universal for all age groups—infants, children, and adults receive the identical weight-based calculation 1, 3
• Using the standard 150 IU/mL concentration, convert total IU to volume (mL) by dividing by 150 4, 2
• For example, an 80 kg patient requires 1,600 IU (approximately 10.6 mL), typically assembled from five 2-mL vials plus a partial sixth vial 1

Route of Administration

Wound Infiltration (Primary Route)

• Infiltrate the entire calculated HRIG dose thoroughly around and into all bite wounds if anatomically feasible 1, 2
• This local wound infiltration is critical—rare PEP failures have been linked to inadequate wound infiltration 1
• Radiotracer studies demonstrate significant retention and local diffusion of HRIG at injection sites for at least 24 hours, supporting the importance of wound infiltration 5

Intramuscular Injection (For Remaining Volume)

• Inject any remaining HRIG volume intramuscularly at a site distant from the vaccine administration site 1, 2
• Use a separate needle for the intramuscular injection 2

Critical Administration Rules

• Never administer HRIG in the same syringe or at the same anatomical site as the rabies vaccine—co-administration interferes with active antibody production 1, 3, 2
• Never exceed 20 IU/kg—higher doses partially suppress the vaccine-induced antibody response and may compromise protection 1, 3, 2
• Discard any remaining product after dose administration 2

Timing of Administration

• Ideal timing: Day 0 (the same day as the first rabies vaccine dose) 1, 3
• Acceptable window: Up to and including day 7 after the first vaccine dose if initially missed 1, 3
• After day 7: Do not give HRIG—vaccine-induced antibodies are presumed to have developed, and additional passive antibody may suppress the active immune response 1, 3

Complete Post-Exposure Prophylaxis Regimen

For Previously Unvaccinated Patients

• HRIG 20 IU/kg on day 0 plus four doses of rabies vaccine (1.0 mL intramuscularly) on days 0,3,7, and 14 1, 6
• Administer vaccine in the deltoid muscle for adults and older children, or anterolateral thigh for young children 1, 6
• Never use the gluteal area for vaccine—this produces inadequate antibody response and vaccine failure 1, 6

For Previously Vaccinated Patients

• Do not give HRIG—it will inhibit the anamnestic antibody response 1, 3
• Give only two vaccine doses on days 0 and 3 1, 3

For Immunocompromised Patients

• Give HRIG 20 IU/kg on day 0 plus five vaccine doses on days 0,3,7,14, and 28 1, 3, 6
• This applies even if previously vaccinated 3, 6

Common Implementation Errors

• A 2020 multi-hospital study found that while 98% of patients received the correct HRIG dose, only 56% received proper wound infiltration—this is a critical gap that may reduce prophylactic effectiveness 1
• Failure to infiltrate wounds with the full calculated dose has been linked to rare PEP failures 1
• Exceeding the 20 IU/kg dose suppresses active antibody production 1, 3, 2

Immediate Wound Care

• Before administering HRIG or vaccine, thoroughly wash all wounds with soap and water for at least 15 minutes—this is the single most effective measure for preventing rabies infection 1, 6
• Follow with irrigation using a virucidal agent such as povidone-iodine solution if available 3, 6

Efficacy

• When the complete PEP regimen (HRIG plus vaccine series) is initiated promptly and administered correctly, it is nearly 100% effective at preventing clinical rabies 1, 6
• No PEP failures have been documented in the United States since modern cell-culture vaccines and HRIG were licensed when the protocol is properly followed 1