Pharmacokinetics of the toxic fraction of Centruroides limpidus limpidus venom in experimentally envenomed rabbits and effects of immunotherapy with specific F(ab')2.

Envenomations after scorpion stings are a major health problem throughout the world. Their specific treatment is immunotherapy which consists of the injection of specific antibody. In this article, we studied the pharmacokinetics of the toxic fraction of Centruroides limpidus limpidus venom (fraction II) in experimentally envenomed rabbits. After an intravenous injection, fraction II (FII) was rapidly distributed and eliminated from the body (terminal half-life of 1.9 h). When injected subcutaneously, high concentrations of FII were measured in the vascular space rapidly after the injection (Tmax = 1 h) and FII was eliminated with a terminal half-life of 1.8 h, close to that determined after intravenous injection. These observations go along with the rapid onset of clinical symptoms observed after accidental envenomations. To investigate the mechanism of action of antivenom, we examined the effects of the intravenous administration of antivenom (horse F(ab')2 directed against Centruroides venoms) on the pharmacokinetics of FII. Immunotherapy performed 2 h after the experimental envenomation largely increased the area under the concentration time curve of FII compared to that calculated in absence of immunotherapy (13,000 versus 170 ng h ml(-1), respectively). These observations agree with previous findings which showed that specific antibody fragments are able to remove drugs from their site of action and sequester them in the vascular space. These studies provide a powerful tool to determine an excellent procedure for further improvement of immunotherapy.