In this episode, I’ll discuss when rabies immune globulin is indicated.
Rabies immune globulin (RIG) administration is part of successful rabies post-exposure prophylaxis. The rabies vaccine produces active immunity beginning about 7 to 10 days after the vaccine series is started. However, when RIG is given, passive immunity is instantly provided by virus-neutralizing antibodies present in the RIG. Because the half-life of RIG is about 3 weeks, the passive immunity lasts long enough until active immunity via vaccine response can be generated.
Whenever questions arise regarding rabies post-exposure prophylaxis, I always contact the local health department from the county the patient is from for guidance. The CDC maintains a listing of state and local contacts regarding rabies consultation on this page. With frequent rabies vaccine and RIG product shortages, contacting the local health department may be an essential step in managing these drug shortages.
The dose of RIG is 20 units/kg x 1. For maximum efficacy, RIG should be administered as a local infiltration to the bite wound. This may not always be anatomically feasible, but it does provide for the highest rate of virus neutralization.
Whatever RIG cannot be infiltrated around the wound may be administered IM in the deltoid muscle of the upper arm or lateral thigh muscle.
For an exceptionally small wound site such as a finger, a small dose of 0.5 mL may be infiltrated around the wound.
For an exceptionally large wound, the RIG may first be diluted so that there is enough volume to infiltrate the entire wound. Be sure to check the prescribing information of the exact product being used as some brands should be diluted with normal saline and others 5% dextrose.
In the extremely rare event that IM administration is felt to be contraindicated such as in a patient with an uncorrectable bleeding disorder, consideration may be given to subcutaneous administration. Due to a lack of clinical data that supports this, I would only consider it in consultation with health department officials.
If there is no obvious bite wound (this is often the case with bat exposure) the entire dose of RIG is administered IM in the deltoid muscle of the upper arm or lateral thigh muscle.
In any case, when giving RIG in the deltoid it must be given in the opposite deltoid as the one that received the rabies vaccine. This is because RIG given at the same site of the vaccine will attenuate the ability of the rabies vaccine to provide an immune response. For the same reason, RIG should not be given after starting a rabies vaccine series.
A delay of fewer than 7 days between the first vaccine and the administration of RIG is acceptable according to manufacturers and this may occasionally be necessary when the proper amount of RIG was not immediately available for a patient being vaccinated.
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