Intravenous human rabies immunoglobulin for post-exposure prophylaxis: serum rabies neutralizing antibody concentrations and side-effects

The beneficial effect of passive immunization for post-exposure rabies prophylaxis is associated with the appearance of serum neutralizing antibody (SNA) earlier than occurs with vaccine alone. We compared the SNA response and the side-effects in 30 previously unimmunized healthy volunteers given a commercially available human rabies immunoglobulin (HRIG) intramuscularly (i.m.) or an experimental HRIG prepared by DEAE Sephadex column chromatography, intravenously (i.v.) with or without human diploid-cell culture rabies vaccine (HDCS). The subjects were divided into five equal groups: HDCS alone, HDCS + i.m. HRIG 20 IU/kg (currently recommended) i.v. HRIG alone 15 IU/kg, HDCS + i.v. HRIG 15 IU/kg or HDCS + HRIG 5 IU/kg i.v. plus 10 IU/kg i.m. to simulate local bite wound infiltration. HDCS, 1·0 ml, was injected subcutaneously (s.c.) on days 0, 3, 7, 14 and 28. Only local discomfort at injection sites was observed without differences between groups. SNA was demonstrated in all HRIG recipients at day 1, but the concentrations were higher in those receiving it intravenously. No difference in the SNA response to vaccine was observed between the i.v. and i.m. HRIG groups given the same vaccine lot. It would appear that i.v. HRIG 15 IU/kg can be substituted for i.m. HRIG 20 IU/kg for post-exposure prophylaxis. Since the current regimen is almost 100% protective, there is noway of proving that i.v. HRIG 15 IU/kg is more efficacious. The immediate SNA level and economy are the chief advantages of i.v. HRIG 15 IU/kg.