How much immunoglobulin should be administered after a tick bite? - briefly
Administer human rabies immune globulin at 20 IU per kilogram of body weight, infiltrating as much as possible into the bite site and giving the remainder intramuscularly. Dosage is calculated according to the patient’s weight, with the remaining volume injected at a distant site.
How much immunoglobulin should be administered after a tick bite? - in detail
The recommended amount of rabies immune globulin (RIG) after a tick bite that poses a rabies risk is calculated on body weight: 20 IU of human rabies immune globulin per kilogram, not to exceed 2 000 IU total. The dose is administered once, at the time of the first vaccine injection.
Typical calculations:
- Adult weighing 70 kg → 70 kg × 20 IU/kg = 1 400 IU (below the 2 000 IU ceiling).
- Child weighing 15 kg → 15 kg × 20 IU/kg = 300 IU.
- Person weighing 110 kg → 110 kg × 20 IU/kg = 2 200 IU, but the dose is capped at 2 000 IU.
Administration details:
- Infiltrate as much of the calculated dose as possible directly around and into the wound(s) caused by the tick.
- Any remaining volume is given intramuscularly at a site distant from the vaccine injection.
- The RIG preparation (human HRIG) is typically supplied at a concentration of 150 IU/mL; therefore, the volume to inject equals the total IU divided by 150. For a 70‑kg adult, 1 400 IU ÷ 150 IU/mL ≈ 9.3 mL.
Timing: the immunoglobulin must be administered as soon as feasible after exposure, ideally within seven days, and must precede or coincide with the first dose of the rabies vaccine series.
Key points for clinicians:
- Verify the product is human-derived (HRIG) rather than equine, to reduce adverse‑reaction risk.
- Ensure the calculated dose does not surpass the 2 000 IU maximum, regardless of patient weight.
- Document the exact volume infiltrated into the wound and the site of any remaining injection.
Adherence to these dosage and administration guidelines provides passive immunity that bridges the interval until active immunity develops from the vaccine series.