Analysis of therapeutic benefits of antivenin at different time intervals after experimental envenomation in rabbits by venom of the brown spider (Loxosceles intermedia).

Bites by the brown spider (Loxosceles spp.) are an important health problem in South America, where three species predominate (Loxosceles laeta, Loxosceles gaucho, Loxosceles intermedia). Brown spider bites (loxoscelism) induce a block of cutaneous necrosis and, less commonly, may cause fatal systemic poisoning. A variety of controversial protocols are used to treat loxoscelism, while treatment with antivenin is the only venom specific treatment. Here we studied the action of the venom as well as the response to the antivenin for Loxosceles through an experimental study that simulates bites of L. intermedia (bites of this species are the most common in Brazil). Beneficial effects are known for antivenin applied quickly (within 4 h) after envenomation. Here we wished to examine the temporal development of the brown spider bite as well as the temporal patterns of the action of the antivenin to determine the time limits for beneficial use of the antivenin after envenomation. This information is important since most patients only appear for treatment several hours after being bitten. New Zealand rabbits were experimentally exposed to the venom from brown spiders by the injection of venom from L. intermedia (2x minimum necrotic dose), followed at regular time intervals by antivenin. The use of the loxoscelic antivenin--CPPI (4 mL per animal)--minimized the effects of envenomation when applied for up to 12 h after the injection of the venom, as evaluated by cutaneous (erythrema, edema, ecchymosis and necrosis) and systemic (blood cell and platelet counts, hematimetrics and fibrinogen dosage) criteria. Also, antivenin reduced the size of the necrotic area when applied up to 48 h after envenomation. Thus, therapy with loxoscelic antivenin, CPPI, may provide beneficial results by interfering with envenomation well after the bite occurred and therefore may become an important tool for medical treatment of brown spider bites.