The potency of
antivenoms is assessed by analyzing the neutralization of
venom-induced lethality, and is expressed as the Median Effective Dose (ED50). The present study was designed to investigate the pathophysiological mechanisms responsible for lethality induced by the
venom of Bothrops asper, in the experimental conditions used for the evaluation of the neutralizing potency of
antivenoms. Mice injected with 4 LD50s of
venom by the intraperitoneal route died within ∼25 min with drastic alterations in the abdominal organs, characterized by
hemorrhage, increment in plasma extravasation, and hemoconcentration, thus leading to
hypovolemia and cardiovascular collapse.
Snake venom metalloproteinases (SVMPs) play a predominat role in lethality, as judged by partial inhibition by the
chelating agent CaNa2EDTA. When
venom was mixed with
antivenom, there was a
venom/
antivenom ratio at which
hemorrhage was significantly reduced, but mice died at later time intervals with evident hemoconcentration, indicating that other components in addition to SVMPs also contribute to plasma extravasation and lethality. Pretreatment with the
analgesic tramadol did not affect the outcome of the neutralization test, thus suggesting that prophylactic (precautionary)
analgesia can be introduced in this assay. Neutralization of lethality in mice correlated with neutralization of in vitro
coagulant activity in human plasma.