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INTRODUCTION

Centruroides exilicauda (formerly known as Centruroides sculpturatus) is the only scorpion of medical importance in the United States. It is indigenous to the deserts of Arizona, but also can be found in Texas, New Mexico, California, and Nevada.10 Occasionally, envenomations occur in nonindigenous areas of the country from “stowaway” scorpions in travelers’ luggage.34

HISTORY

Poison control centers in Arizona receive several thousand calls annually for scorpion stings. Although the incidence of morbidity with these envenomations is significant, no deaths associated with the toxic effects of scorpion venom have been reported in the United States for almost 50 years. Antivenom for the Centruroides spp was first produced in horses in Mexico in the 1930s.12 In 1947, antivenom was produced from rabbits and cats immunized with C. sculpturatus and C. gertschi.31 The Antivenom Production Laboratory at Arizona State University (APL-ASU) began producing antivenom to C. sculpturatus in goats in 1965. This antivenom was used for treatment of scorpion stings in Arizona until 2004, when production ceased and stockpiles expired. In June 2000, Silanes Laboratory received orphan drug status for a C. scorpion antivenom, an equine F(ab′)2 derived from C. limpidus, C. noxius, C. suffusus, and C. meisei (formerly known as C. elegans) manufactured by Instituto Bioclon of Mexico, and sold as Anascorp. In August 2011, Anascorp was approved by the US Food and Drug Administration (FDA) for the treatment of C. exilicauda envenomations.16

PHARMACOLOGY

Antivenom for scorpions is prepared in the same manner as other antivenom products (Antidotes in Depth: A37 and A39).

Pharmacokinetics and Pharmacodynamics

In a study of 8 healthy patients (6 males and 2 females, age 17–26 years) without prior scorpion envenomation, an intravenous bolus dose of 47.5 mg of Anascorp was administered. Serial blood samples were collected over 21 days. Measured pharmacokinetic parameters (mean ± standard deviation) included area under the curve (AUC), 706 ± 352 mcg/mL; clearance, 83.5 ± 38.4 mL/h; half-life, 159 ± 57 hours; and steady-state volume of distribution (Vdss), 13.6 ± 5.4 L.35

ROLE IN CENTRUROIDES SPECIES

One vial of Anascorp antivenom contains sufficient F(ab′)2 to neutralize 150 mouse LD50 of Centruroides venom.26 Safety and efficacy are documented in both animals and humans.1,8-10 In the FDA review and subsequent approval of Anascorp, 6 trials were submitted for evaluation. Only one study was prospective, randomized, double-blinded, and controlled. It demonstrated a clear benefit in reduction of signs and symptoms of scorpion envenomation by 4 hours post-administration (8/8 vs 1/7), reduction in quantity of sedative administered (mean midazolam dose of 0.1 mg/kg (0.0–0.2 mg/kg) in treated patients versus 4.6 mg/kg (0.1–16.7 mg/kg) in controls. It absence of free serum venom concentrations at one hour after administration (mean 0.0 in ...

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