Envenomation by Echis coloratus (Mid-East saw-scaled viper): a review of the literature and indications for treatment.

Envenomation by the snake Echis coloratus causes a local swelling and hemostatic failure. Most cases recover uneventfully, however about one-third of the victims bleed or develop anemia, and one known death due to renal failure has been reported. Uncontrolled observations suggest that treatment by a specific antivenom reduces the duration of the hemostatic failure. Still the management of victims of E coloratus remains uncertain. Some authors advocate antivenom treatment for all patients, while others recommend its use only in the event of complications. We review reported data on the effect of the venom in vitro, in laboratory animals and in humans, and reexamine alternative treatment strategies by applying a revised version of a published decision model. The probability of bleeding and the efficacy of antivenom treatment were the main determinants in the choice between antivenom treatment and expectant management of victims of E. coloratus. Assuming a therapeutic efficacy of 32%, the decision model favored antivenom treatment when the risk of bleeding exceeded 7.5%. The estimated risk of bleeding exceeds this threshold in patients who present with either proteinuria, a blood urea of > 7 mmol/l, a platelet count of < 100,000/microliters, or a hemoglobin level of < 13 g/dl. In patients who had been exposed to antiserum in the past, or in whom the annual probability of future envenomation exceeds 0.9%, antivenom treatment was preferred only when bleeding was certain. Errors in our estimates of the efficacy of antivenom treatment, of the mortality after a bleeding event and of the risk of anaphylaxis after a repeated exposure to antiserum may have affected our conclusions. Nonetheless, they are consistent with presently available information and, pending more reliable estimates, may be considered as guidelines for treatment.