## Post-Exposure Prophylaxis for Rabies **Key Point:** Human rabies immunoglobulin (HRIG) is the first-line passive immunization agent for post-exposure rabies prophylaxis. It provides immediate neutralizing antibodies against rabies virus. ### Mechanism of HRIG - Provides immediate passive immunity via pre-formed neutralizing antibodies - Binds to viral glycoproteins and prevents viral entry into neurons - Must be administered as soon as possible after exposure (ideally within 24–48 hours, but can be given up to 7 days) - Dose: 20 IU/kg body weight ### Administration Protocol - Infiltrate around the wound site (50% of dose) - Administer remainder intramuscularly in the gluteal region - Always given alongside active immunization (rabies vaccine series) - Most effective when combined with rabies vaccine (cell culture vaccine or purified chick embryo cell vaccine) **High-Yield:** HRIG is a **passive immunoglobulin** — it works immediately but provides only short-term protection (half-life ~21 days). Active vaccination (rabies vaccine) must follow to generate long-term immunity. **Clinical Pearl:** In India, HRIG is often in short supply. When unavailable, equine rabies immunoglobulin (ERIG) or rabies monoclonal antibodies may be used as alternatives, though HRIG is preferred due to lower risk of serum sickness. ### Why HRIG is Superior to Other Agents | Agent | Role in Rabies PEP | Timing | |---|---|---| | HRIG | Passive immunity (immediate) | Within 7 days of exposure | | Rabies vaccine | Active immunity (delayed) | Series over 14–28 days | | Ribavirin | Antiviral (limited efficacy) | Not first-line for PEP | | Acyclovir | Herpes virus agent | No activity against rabies | **Mnemonic:** **HRIG = Hyperimmune Rabies Immunoglobulin** — passive, immediate, infiltrate the wound.
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