Changes in coagulation effects by venoms of Crotalus atrox as snakes age.

Venom samples separately collected at monthly intervals from three Crotalus atrox specimens as they aged from 2 to 22 months showed many quantitative changes of biological activities. But more important were qualitative changes of coagulation activity. Up to 8 months the venoms clotted fibrinogen solutions directly. At 9 to 10 months, plasma was clotted but not fibrinogen. Subsequently the venoms no longer clotted plasma. Qualitative venom changes with growth of snakes could explain some of the conflicting reports both on clinical aspects of snake bite in man and on experimental venom work. The findings emphasize the importance for clinicians dealing with snake bite to monitor the clot-quality of their patient's blood--a simple bedside test for defibrinogenation, no-clot indicating zero fibrinogen and speck-clot representing fibrinogen concentrations under 50 mg/100 ml. With strongly defibrinating venoms, non-clotting blood is a very sensitive sign of systemic envenoming. In contrast, the relatively feeble defibrinating activity of juvenile C. atrox venom suggests that, if the blood is non-clotting in C. atrox bites, this indicates the victim has received a potentially lethal or near-lethal dose of venom urgently requiring effective antivenom therapy.