Black Widow Spider Antivenin for Patients With Systemic Latrodectism

Inclusion Criteria: * Moderate to severe pain intensity measured using the visual analog scale (VAS score ≥ 40mm) at the start of screening phase (VAS 0) * Diagnosis of latrodectism by the Investigator, with concurrence of diagnosis by a physician not directly involved with the study * Moderate to severe pain intensity measured using the visual analog scale (VAS score ≥ 40mm) at Baseline (VAS 1) Exclusion Criteria: * Less than 10 years of age * Presents to the emergency department of any healthcare facility greater than 24 hours after onset of symptoms * Has a known (self-reported) hypersensitivity to fentanyl, morphine, diazepam, or equine serum * History of significant cardiac, respiratory, hepatic or renal disease, psychiatric disorder or chronic pain syndrome that in the investigator's assessment would confound efficacy or safety endpoint assessment (e.g., a bite to the leg of a patient with reflex sympathetic dystrophy) * History or suspected history or substance abuse * Pregnant or breast-feeding * Has a distracting injury with acute pain, or is unable to make a reliable self-report of pain intensity to pain relief based solely on the condition of interest * Was already treated with Merck Antivenin Latrodectus Mactans for signs/symptoms related to the current widow spider bite * Unable to provide a telephone number to be contacted for follow-up interviews on Days 2, 10, and 17 after discharge from the emergency department