Pharmacological analysis of Poecilotheria spider venoms in mice provides clues for human treatment.

Bites of tiger spiders belonging to Poecilotheria genus cause moderate to severe pain and long-lasting local or generalized muscle cramps in humans. Bites occur in regions of the spiders' natural habitat, India and Sri Lanka, but the popularity of these colorful tarantulas as pets leads to reports of envenomation cases worldwide. Treatment is predominantly symptomatic and often inadequate since there is almost no clinical or toxicology research data available, and physicians outside India or Sri Lanka typically have no experience in treating such cases. We report toxicity studies of venom from nine Poecilotheria species in laboratory mice (Mus musculus Balb/C males). LD50 values are 5-14 mg of lyophilized crude venom per 1 kg (i.v.). The major symptoms of envenomation include tonic-clonic seizures, jerks, characteristic motor stereotypy, and hyperalgesia and point to voltage-gated sodium channels as a potential target of the venom components. Poecilotheria fasciata venom effects were studied in detail at a sub-lethal dose of 5 mg/kg (LD50 = 12 mg/kg). 13 widely used pharmacological agents (atropine, chloropyramine, chlorpromazine, diazepam, ethanol, flupirtine, haloperidol, ketotifen, lamotrigine, oxcarbazepine, tolperisone, xylazine, and CaCl2) were checked for ability to suppress the envenomation symptoms. Chlorpromazine (10 mg/kg, i.p.), oxcarbazepine (60 mg/kg, p.o.), tolperisone (50 mg/kg, s.c.) and xylazine (2.5 mg/kg, i.p.) were found effective as a pretreatment to mitigate muscle cramps and motor stereotypy. When administered after envenomation chlorpromazine (5 mg/kg, i.v.) effectively reduced the cramps, while oxcarbazepine (30 mg/kg, i.v.) and xylazine (1 mg/kg, i.v.) suppressed the stereotypy.