Initial studies of the prophylactic effect of parenterally administered respiratory syncytial virus (RSV)-
neutralizing antibodies in cotton rats indicated that virus replication in lung tissues was restricted when animals with preexisting antibody titers in serum of 1:100 or more (as measured by plaque reduction) were challenged intranasally with 10(4) PFU of virus. Subsequently, a
therapeutic effect of parenterally administered RSV
antibodies (present in human
gamma globulin) was demonstrated in both cotton rats and owl monkeys. Parenteral inoculation of RSV-infected cotton rats or owl monkeys with purified human
immunoglobulin licensed for
intravenous administration in humans (
IVIG) effected
a 10(-1.7) to 10(-2.7) reduction in the level of pulmonary virus at the height of
infection. Because of these encouraging results, we examined
topical administration of
IVIG to determine whether it was also effective and whether it offered an advantage over the parenteral route with regard to simplicity and the dose required for full
therapeutic effect.
IVIG (0.025 g/kg) administered topically by the intranasal route to anesthetized cotton rats at the height of
RSV infection effected a 10(2.2)-fold reduction in viral titers of pulmonary tissues and a complete clearance of detectable virus in 92% of the animals within 24 h. In contrast, 4 g of
IVIG per kg was required to produce a comparable
therapeutic effect when the material was administered parenterally. Thus, the
therapeutic effect of
IVIG was 160 times greater by the topical route than by parenteral inoculation.