What is the recommended dose and administration of anti-rabies serum (equine) for post-exposure prophylaxis?

Anti-Rabies Serum (Equine) for Post-Exposure Prophylaxis

Recommended Dose

The recommended dose of equine rabies immunoglobulin (ERIG) is 20 IU/kg body weight, administered once at the beginning of post-exposure prophylaxis, applicable to all age groups including children. 1

• This 20 IU/kg formula is the same standard dose used for both human rabies immunoglobulin (HRIG) and equine rabies immunoglobulin (ERIG). 1
• The dose should never exceed the recommended amount, as rabies immunoglobulin can partially suppress active antibody production from the vaccine. 1

Administration Technique

As much of the calculated dose as anatomically feasible should be thoroughly infiltrated into and around the wound site, with any remaining volume administered intramuscularly at a site distant from the vaccine injection. 1

• This infiltration at the wound site is critical—treatment failures have been documented when less than the full amount of rabies immunoglobulin was infiltrated at exposure sites. 1, 2
• ERIG must never be administered in the same syringe or at the same anatomical site as the rabies vaccine. 1, 2
• For intramuscular administration of any remaining volume, use a site distant from where the vaccine is given. 1

Timing of Administration

• ERIG should be given as soon as possible after exposure, ideally at the time the first vaccine dose is administered. 1
• If not given initially, ERIG can still be administered up to and including day 7 after the first vaccine dose. 1
• Beyond day 7, ERIG is not indicated because an antibody response to the cell culture vaccine is presumed to have occurred. 1

Complete Post-Exposure Prophylaxis Regimen

For previously unvaccinated persons, post-exposure prophylaxis consists of thorough wound cleansing, ERIG administration, and a complete vaccine series. 2

• The vaccine schedule is 5 doses administered on days 0,3,7,14, and 28 for standard patients. 2
• A 4-dose schedule (days 0,3,7, and 14) is now recommended for immunocompetent previously unvaccinated persons, though the 5-dose schedule remains appropriate for immunocompromised patients. 1, 3
• Vaccines should be administered intramuscularly in the deltoid area for adults; the anterolateral thigh is acceptable for children. 2
• Never administer vaccine in the gluteal area, as this results in lower neutralizing antibody titers. 2

Safety Profile and Adverse Reactions

Purified equine rabies immunoglobulin (ERIG) has been used effectively worldwide with a low incidence of adverse reactions (0.8%-6.0%), most of which are minor. 2

• Common adverse events include local pain, erythema, itching, headache, body ache, fever, and malaise—all typically mild and self-limited. 4
• Serum sickness-like reactions can occur, typically around day 8, presenting with urticarial or maculopapular rash, low-grade fever, arthralgias, and sore throat. 5
• These reactions respond well to antihistamines and a short course of corticosteroids. 5

Critical Distinction: Purified vs. Unpurified Products

• Unpurified antirabies serum of equine origin is associated with higher rates of serious adverse reactions, including anaphylaxis. 2
• Purified ERIG has a significantly better safety profile and should be used when available. 2

Clinical Efficacy

When administered properly with wound care and vaccine, ERIG has been used effectively worldwide to prevent rabies, with no documented treatment failures in the United States when current protocols are followed. 2

• Cell culture vaccines combined with ERIG have been used successfully to treat persons bitten by rabid animals globally. 2
• WHO estimates that 10-12 million persons receive post-exposure prophylaxis annually worldwide. 2
• Treatment failures abroad have occurred only when deviations were made from recommended protocols, specifically: failure to cleanse wounds properly, vaccine administered in gluteal area instead of deltoid, or inadequate RIG infiltration at wound sites. 2

Essential Wound Management

Thorough wound cleansing with soap and water is critical and markedly reduces rabies risk even without other prophylaxis. 2

• Immediate gentle irrigation with water or dilute povidone-iodine solution significantly decreases infection risk. 2
• Wound cleansing alone has been shown to markedly reduce the likelihood of rabies in animal studies. 2
• Suturing should be avoided when possible. 2

Previously Vaccinated Persons

Persons who have previously received complete rabies vaccination (pre-exposure or post-exposure with cell culture vaccine) should receive only vaccine—no ERIG. 2, 1

• ERIG is contraindicated in previously vaccinated individuals as it may interfere with the anamnestic antibody response. 1

Common Pitfalls to Avoid

• Do not delay administration—post-exposure prophylaxis is a medical urgency, though not an emergency. 2
• Do not exceed the recommended 20 IU/kg dose of ERIG, as this can suppress active antibody production. 1
• Do not fail to infiltrate wounds adequately—this is associated with treatment failures. 2, 1
• Do not administer ERIG and vaccine at the same site—use separate anatomical locations. 1
• Do not use unpurified equine serum when purified ERIG is available due to higher anaphylaxis risk. 2