A controlled trial of topical nitroglycerin in a new Zealand white rabbit model of brown recluse spider envenomation

Study objectives: Topical nitroglycerin has been reported to prevent skin n ecrosis from brown recluse spider bites, but this has never been scientific ally tested. This study attempts to assess the effects of topical nitroglyc erin on experimental Loxosceles reclusa envenomations. Methods: We performed a randomized, blinded, controlled study in an animal care facility. Twenty-four New Zealand white rabbits were experimentally en venomated by means of subcutaneous injection with 20 mug of brown recluse s pider venom. Rabbits were randomized to 1 of 2 experimental groups. The tre atment group received 1 in of 2% topical nitroglycerin ointment every 6 hou rs for 3 days applied directly to the envenomation site. The control group received the vehicle without nitroglycerin. Gross examination of the lesion s and measurements of the areas of the lesions were made daily. Creatine ph osphokinase (CPK), blood urea nitrogen, creatinine, hemoglobin, and hematoc rit levels were measured on days 0, 5, and 10. Lesions were excised after 1 0 days and examined by a blinded pathologist, who measured the area of necr osis and quantified inflammation and edema using a standard wound-healing s core. For all values, mean values plus SD were determined. All comparisons made over multiple time points were assessed for significance by using a re peated-measures analysis of variance followed by Fisher least significant d ifference and Scheffe post hoc comparisons. A P value of .05 or less was us ed to determine significance. The Student's t test was used to compare the means of single measures. Significance was determined by using 95% confiden ce intervals. Comparisons of total area of necrosis were made with the nonp arametric Mann-Whitney U test because of the heavy positive skew of the dat a. Results: Skin necrosis developed in all animals. Mean values of the lesion area were not significantly different over time between the 2 groups of ani mals. At day 10, the median area of necrosis was 22.3 cm(2) for the treatme nt group and 15.4 cm(2) for the control group (P=.12). The inflammation sco re was 3.33+/-0.78 for the treatment group and 2.79+/-1.29 for the control group (P<.01). The edema score was 1.25+/-1.28 for the treatment group and 0.98+/-1.10 for the control group (not significantly different). CPK levels increased dramatically in both groups, with the greatest increase in the t reatment group. In bath groups hemoglobin and hematocrit levels decreased s ignificantly, whereas WBC counts and platelet counts increased significantl y, without significant differences between the 2 groups. Conclusion: At the dose used in this experiment, topical nitroglycerin did not prevent skin necrosis, increased inflammation score, and increased seru m CPK levels. The results of this study do not support the use of topical n itroglycerin in the treatment of L reclusa envenomation and suggest that sy stemic toxicity could be increased.