How is the dose of immunoglobulin calculated for a tick bite? - briefly
The amount of rabies immunoglobulin administered after a tick bite is calculated by multiplying the patient’s body weight (in kilograms) by 20 IU, delivering the total dose intramuscularly at the wound site and the remainder into a distal muscle. This weight‑based regimen is given on days 0, 3, 7, 14, and 28 as part of the standard post‑exposure prophylaxis schedule.
How is the dose of immunoglobulin calculated for a tick bite? - in detail
Determining the appropriate amount of immunoglobulin after a tick attachment requires several patient‑specific parameters. The calculation proceeds as follows:
- Identify the type of prophylaxis needed: rabies post‑exposure prophylaxis (PEP) or prevention of tick‑borne bacterial infections such as Lyme disease. Immunoglobulin is indicated only for rabies PEP in individuals who have not been previously vaccinated.
- Record the patient’s body weight in kilograms. The standard recommendation for human rabies immune globulin (HRIG) is 20 IU per kilogram of body weight.
- Multiply the weight by the unit factor. For example, a 70 kg adult receives 1 400 IU of HRIG.
- Convert international units to milliliters based on the product’s concentration (commonly 150 IU/mL). Using the previous example: 1 400 IU ÷ 150 IU/mL ≈ 9.3 mL.
- Administer the calculated volume infiltrated around the wound site(s). If multiple bite locations exist, distribute the total volume proportionally, ensuring each site receives at least 0.1 mL per cm² of wound surface.
- Document the exact dose, concentration, and administration site in the medical record.
Additional considerations:
- For pediatric patients, weight‑based dosing remains the same; ensure accurate measurement to avoid under‑ or overdosing.
- In cases of severe local reaction or contraindication to HRIG, consider alternative passive immunization strategies while maintaining the same IU/kg target.
- Verify that the immunoglobulin product is within its expiration date and stored according to manufacturer guidelines before preparation.
The described methodology yields a precise, weight‑adjusted immunoglobulin volume, aligning with current rabies prophylaxis guidelines and minimizing the risk of insufficient neutralizing antibody levels.