New procedures and parameters for better evaluation of Androctonus australis garzonii (Aag) and Buthus occitanus tunetanus (Bot) scorpion envenomations and specific serotherapy treatment.

New procedures describing intoxication with variable amounts of scorpion venoms (from 1 to 5 LD50) allowed us to introduce new parameters to evaluate Aag and Bot envenomations. Significant differences between the fatal limit time (FLT) and the last mortality time (LMT) were observed when the amount of Aag and Bot venom injected was equal to 1 LD50 and equal to or higher than 2 LD50. For Aag and Bot, the percentage of the fast mortality (FM) and the delayed mortality (DM) varied conversely when the amount of injected venom increased from 1 to 5 LD50. The relationship between the venom LD50 (from 2 to 20), the median protective dose (PD50) and the neutralizing activity of specific antivenom have been established. PD50 increased in a parallel manner with LD50. The neutralizing titres (LD50/ml) of Aag antivenom decreased from 74 +/- 3 to 44 +/- 2 and that of Bot antivenom from 52 +/- 2 to 36 +/- 1 when the number of LD50 injected increased from 2 to 20. Antivenom potency was evaluated using different protocols based on the presence or the absence of preincubation of the venom with the antivenom. In experiments where venom and antivenom were simultaneously but immediately injected, PD50 were twice as high as those found when venom and antivenom were preincubated (30 min at 37 degrees C). On the contrary, the corresponding neutralizing titres were two times lower. In an attempt to simulate accidental envenomations and subsequent serotherapy, Aag and Bot venom (4 LD50) were subcutaneously injected and the appropriate PD50S of antivenom were intravenously administered at different time intervals after envenomation. When the time of antivenom administration was shorter than the FLT, all envenomed mice might be protected by increasing volume of antivenom. However, when the antivenom is injected closer to the FLT only 50 to 60% of mice envenomed, respectively, by Aag and Bot could be saved even when more than 5 PD50 were injected.