Human Rabies Immunoglobulin
Overview
Human rabies immunoglobulin is a plasma-derived immunoglobulin preparation that provides passive immunity against rabies virus by supplying ready-made neutralizing antibodies. It belongs to the class of human immunoglobulin biologics and is used as part of rabies post-exposure prophylaxis in individuals who have not been previously vaccinated. The antibodies bind to rabies virus at the site of exposure and in surrounding tissues, helping prevent viral entry into peripheral nerves and subsequent spread to the central nervous system. It is administered by intramuscular injection, with as much of the calculated dose as possible infiltrated into and around the wound. Its clinical importance lies in offering immediate protection during the window before active immunity develops from rabies vaccination. Because rabies is almost universally fatal once clinical symptoms appear, timely administration of human rabies immunoglobulin in appropriate exposure settings is considered a critical life-saving intervention.
Background and Date of Approval
Human rabies immunoglobulin was licensed in the United States by the Food and Drug Administration on June 12, 1974 for use in combination with rabies vaccine as part of post-exposure prophylaxis. Its development followed evidence that passive antibody administration significantly improves protection when given promptly after rabies exposure. Regulatory authorities including the European Medicines Agency and national regulatory bodies in multiple countries have approved human rabies immunoglobulin preparations based on demonstrated potency, safety, and efficacy in preventing rabies when used according to recommended protocols. International standards for rabies immunoglobulin potency and quality control have been established by the World Health Organization to ensure consistent antibody levels and manufacturing safety. Clinical recommendations for its use are based on decades of global public health data supporting combined passive and active immunization for high-risk exposures.
Uses
Human rabies immunoglobulin is indicated for post-exposure prophylaxis in individuals with suspected or confirmed exposure to rabies virus who have not previously received complete rabies vaccination. It is administered together with a full course of rabies vaccine to provide immediate passive immunity while the vaccine stimulates the body’s own immune response. It is particularly recommended for severe exposures such as bites or scratches that break the skin, contamination of mucous membranes, or other high-risk contact with potentially rabid animals. It is not indicated for individuals who have previously completed an appropriate rabies vaccination series unless there is evidence of inadequate antibody response.
Administration
Human rabies immunoglobulin is administered once at a dose of 20 international units per kilogram of body weight. As much of the dose as anatomically feasible should be infiltrated directly into and around all wound sites to neutralize virus locally, and any remaining volume should be injected intramuscularly at a site distant from the rabies vaccine administration site. It should be given as soon as possible after exposure and ideally at the time of the first vaccine dose. Administration is not recommended beyond seven days after initiation of rabies vaccination because active antibody production is expected to have begun.
Side Effects
Common side effects include pain, tenderness, redness, or swelling at the injection site. Some individuals may experience mild fever, headache, or general discomfort. These reactions are typically mild and self-limiting. The intensity of local reactions may vary depending on the volume administered and anatomical site.
Warnings
Serious adverse reactions are rare but may include hypersensitivity or anaphylactic reactions. Individuals with a history of severe allergy to human immunoglobulin preparations or known IgA deficiency should be evaluated carefully before administration. Immediate medical attention is required if signs of severe allergic reaction occur. Human rabies immunoglobulin should not be repeated within the same post-exposure prophylaxis course as it may interfere with the development of active immunity from the vaccine.
Precautions
Before administration, clinicians should review vaccination history, exposure category, and medical history including allergies. The immunoglobulin and rabies vaccine must be administered at separate anatomical sites using different syringes to prevent interference. Classical drug interactions are uncommon, but immunocompromised individuals may require careful follow-up to ensure adequate immune response. Accurate documentation of dose, timing, and wound infiltration technique is important for optimal prophylactic effectiveness.
Expert Tips
Careful wound assessment and thorough infiltration of immunoglobulin into all bite or scratch sites is critical for effectiveness. Dose calculation must be weight-based and should not exceed the recommended total amount. Coordination with rabies vaccination scheduling is essential to ensure complete post-exposure prophylaxis. Observation for immediate allergic reactions after injection is standard practice. Counselling patients on the importance of completing the vaccine series and recognizing signs of adverse reactions supports safe and effective management.