What is the treatment for a black widow bite?

Treatment of Black Widow Spider Bite

The definitive treatment for black widow spider bites includes seeking immediate medical care for severe symptoms, with black widow spider antivenom being the most effective treatment for moderate to severe envenomation, providing relief within 30 minutes of administration. 1, 2

Initial Assessment and Triage

• Call emergency services immediately if the patient develops systemic symptoms such as difficulty breathing, muscle rigidity, dizziness, or confusion 3
• Seek medical care if:
  • Pain extends beyond the bite site
  • Pain becomes severe and is not controlled by over-the-counter medications
  • An open wound develops
  • Systemic symptoms develop 3

Treatment Algorithm

1. Mild Envenomation (Local Pain Only)

• Remove from exposure to further bites
• Clean the wound thoroughly with soap and water
• Apply ice or cold packs to the bite site (place a thin barrier between ice and skin) 3, 4
• Use over-the-counter pain medications:
  • Acetaminophen or NSAIDs for pain relief 3, 4
  • Topical lidocaine (5%) if skin is intact 3

2. Moderate to Severe Envenomation

• First-line treatment: Black widow spider antivenom (Antivenin Latrodectus mactans)
  • Most effective treatment, providing complete relief usually within 30 minutes 1, 2
  • Significantly shortens duration of symptoms (9 hours with antivenom vs. 22 hours without) 2
  • Reduces hospitalization rates (12% with antivenom vs. 52% without) 2
• Second-line treatment (if antivenom unavailable or contraindicated):
  • IV opioids (e.g., morphine) combined with benzodiazepines 2
  • 55% of patients receiving IV morphine and 70% receiving both IV morphine and benzodiazepines obtained relief without additional medication 2

Clinical Presentation and Monitoring

• Characteristic symptoms of black widow envenomation:
  • Severe pain and muscle cramping
  • Abdominal rigidity without tenderness (hallmark sign)
  • Back pain
  • Hypertension
  • Regional diaphoresis 5, 1
• Monitor for:
  • Signs of anaphylaxis if antivenom is administered (rare but reported) 6
  • Progression of symptoms, which typically peak within 8 hours post-envenomation 5
  • Complete recovery may take weeks in untreated cases 5

Important Considerations and Pitfalls

• Calcium gluconate is ineffective despite historical use as first-line treatment. Studies show 96% of moderate to severe envenomations treated with calcium gluconate required additional pain medication 2
• Antivenom carries a small risk of anaphylaxis but is generally considered safe and effective 6
• Cats are extremely sensitive to black widow venom with high mortality; dogs show severe signs but are more resistant than cats 5
• 15% of bites may be non-envenomating as black widow spiders can control venom injection 5
• First aid alone is of no value in treating black widow envenomation 5

Special Populations

• Children and elderly patients may be more susceptible to severe envenomation
• Patients with pre-existing cardiovascular conditions should be monitored closely due to hypertensive effects of the venom

The evidence strongly supports the use of antivenom for moderate to severe cases despite concerns about hypersensitivity reactions, as it dramatically reduces symptom duration and hospitalization rates compared to other treatments 1, 2.