The efficacy of intramuscular (im) administration of sheep Fab and
IgG antivenoms was assessed in a mouse experimental model of envenomation by Bothrops asper, in order to test if the more rapid absorption of Fab improves neutralization. Both
antivenoms were adjusted to have a similar neutralizing potency in assays involving preincubation of
venom and
antivenom. Neither
antivenom was effective in neutralizing lethality, nor in prolonging the time of death, in mice injected with either 3, 2 or 1.5 LD(50)s of
venom by the intraperitoneal (ip) route, in experiments in which
antivenoms were administered im immediately after envenomation.
Antivenoms were effective in the neutralization of defibrinating activity, even if treatment was performed 30 min after envenomation, with no differences between
IgG and Fab. Regarding neutralization of local effects, i.e. myonecrosis and
hemorrhage, im administration of
antivenoms at a site distant from the
venom-injection site was completely ineffective in reducing the extent of local tissue damage. However, partial neutralization of these effects was achieved if
antivenoms were administered im at the same site of
venom injection, provided treatment was performed immediately after envenomation. Fab
antivenom was slightly more effective than
IgG antivenom in the neutralization of
myotoxicity under these conditions, although a similar efficacy was observed between these
antivenoms regarding neutralization of hemorrhagic effect. Our observations do not evidence major differences in the neutralizing ability of Fab and
IgG antivenoms when applied by the im route, and do not support the hypothesis that im administration of Fab
antivenoms constitutes an effective alternative to treat B. asper envenomations.