Examination of adverse events following black widow antivenom use in California

Following widow spider (Latrodectus sp.) envenomation, local pain, erythema, abdominal pain, rigidity, hypertension, and diaphoresis can be seen. While an effective specific antivenom (AV) is available, its use is limited due to concern of possible severe allergic reaction. We performed the current study to determine rate of adverse effects and the efficacy of AV in patients treated for widow spider envenomation.

Observational case series of the California Poison Control System electronic database from January 1999 to December 2009. All cases of widow spider envenomation treated with AV were included. Age, gender, signs, and symptoms, adjunctive therapy, number of vials of AV given, and adverse reaction to AV were recorded. Descriptive statistical methods were used.

Ninety-six patients received AV, mean age 26 years (0.12-74 years), 76% male. Following widow spider envenomation generalized pain was reported in 91%, erythema at site in 57%, hypertension (≥ 140/90 mmHg) in 43%, muscle rigidity/cramping in 43%, abdominal pain in 41%, tachycardia (≥ 100 bpm) in 23% and diaphoresis in 21%. No patient required more than one vial of AV. One patient developed urticaria to AV halfway through infusion which was immediately discontinued. Another patient developed generalized flushing following completion of infusion but had no other effects. Two other patients reported myalgia and paresthesia. There were no deaths in any patients receiving AV. There was no shortness of breath or respiratory distress, no hypotension or chest pain following AV administration. All patients reported pain relief with AV and did not require additional AV doses.

Our results suggest that Black Widow Spider Antivenin® (Merck) administration is relatively safe with mild to moderate adverse effects seen in only a small percentage of patients. There were no deaths, or severe allergic reactions identified. The retrospective use of poison control system data is a limitation of our study. Further prospective studies are needed to validate our findings and elucidate the full safety profile on this antivenom.