A study of the prothrombin time of patients bitten by Bothrops snakes, principally Bothrops atrox, the fer-de-lance, was undertaken for possible use as a guide to the severity of envenomation and the effectiveness of antivenin medication. Twenty-six cases of snake-bite poisoning, in which prothrombin-time determinations (Quick) were made every 8 hours, were studied. The patients represented two groups: 1) 20 who had been bitten by a snake 8 to 10 hours before admission, some of whom had already received one or two ampules of antivenin, and 2) six patients seen within 3 hours of the bite. The patients received antivenin every 6 to 8 hours. In the first group, the prothrombin time was 5% of normal on admission and reached a peak of 80% at about 40 hours. In the second group, the prothrombin time was 20% of normal on admission, dropped within 8 hours to less than 5% despite intensive antivenin therapy, and then followed the pattern of the larger group. Clinical improvement paralleled the return of prothrombin time to normal. In none of the patients studied did gangrene requiring surgical treatment develop.
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