Toxicon : official journal of the International Society on Toxinology
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A South American rattlesnake bite without clinical manifestations of envenoming (termed 'dry-bite') has not been recognized to occur by the Brazilian Ministry of Health, which recommends the administration of antivenom to all bitten patients. During 36 months of an observational study on South American rattlesnake bites in Minas Gerais, Brazil, 12% of 41 patients with fang marks at the bite-site did not present clinical or laboratory features of envenoming and had no plasma venom detected before specific serotherapy, fulfilling the criteria for the diagnosis of true 'dry-bite'. Data from these preliminary observations suggest that these patients should be correctly diagnosed since they should not be treated with unnecessary and sometimes hazardous and expensive serotherapy.
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The immunoglobulin fractions IgG, F(ab')2 and Fab of scorpion and snake antivenoms possess pharmacokinetic characteristics that are significantly different from their respective venoms. The venoms (and their toxins) are several fold faster in their distribution into the tissues than any of the immunoglobulin fraction. ⋯ Rescue experiments in anaesthetized rats challenged with lethal doses of venoms or toxins and infused with border-line neutralizing doses of antivenoms, showed that rats infused with F(ab')2 completely recovered, those infused with IgG partially rescued and none of the rats infused with Fab survived. It is concluded that F(ab')2 of scorpion and snake antivenoms possess pharmacokinetic characteristics that render it the most suitable for use in serotherapy of scorpion and snake envenoming.
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Australia has a diverse and rich venomous fauna, both terrestrial and marine, including some of the most venomous species in each class. Antivenom is the principal therapy for the majority of medically significant envenomings and is currently supplied through a single source, CSL, Melbourne. Cases of envenoming reported to Australian poisons information centers (PICs) are dominated by spiderbite and insect stings, respectively accounting for 53.7% and 39.3% of all bite/sting calls. ⋯ It is reported as being therapeutically efficacious in 94% of cases, with a single ampoule being used in 76% of cases, 2 ampoules in 18% of cases, and 3 or more ampoules in 6% of cases. Clinical experience suggests only 20% of red back spider bites require antivenom therapy. It is likely that between 5-10,000 bites occur annually.
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Venoms from spiders are an important source of toxins that can help on the dissection of mechanisms involved in neurotransmission. Among them is the venom of the spider Phoneutria nigriventer that contains several toxic fractions with different targets in mammals and/or insects. We here report that one of these fractions (PhTx2) is able to evoke acetylcholine release from rat cortical synaptosomes and that this effect is dependent on extracellular calcium and is inhibited by the sodium channel blocker tetrodotoxin.
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This review treats the general biology, taxonomy, distribution and venom apparatus of the venomous snakes of Central America. Consideration has been given to the chemistry, pharmacology and immunology of the venom, and particular attention is dispensed to the clinical problem, including the treatment, of envenomations by these reptiles.