What are the clinical guidelines for treating spider bites?

Clinical Guidelines for Spider Bite Management

Initial Assessment and First Aid

For most spider bites, treatment focuses on local wound care, pain control, and monitoring for complications—antibiotics are NOT routinely indicated unless secondary bacterial infection develops. 1, 2

Immediate Wound Care

• Thoroughly irrigate the bite wound with copious amounts of warm or room temperature water until all foreign matter is removed 1, 2
• Apply antibiotic ointment and cover with a clean occlusive dressing to reduce infection risk 1, 2
• Remove rings and constricting objects immediately from the affected extremity, as swelling may occur 1, 2
• Elevate the affected area to reduce swelling and accelerate healing 2

Pain Management

• Apply ice to the bite site with a clean barrier between ice and skin for local pain relief 1, 2
• Use over-the-counter acetaminophen or NSAIDs for pain control 1, 2
• Apply topical lidocaine 5% if the skin is intact for additional pain relief 2

Critical Actions to AVOID

• Do NOT apply suction to the bite site—this is ineffective and potentially harmful 1, 2
• Do NOT apply tourniquets or pressure immobilization bandages, as these may worsen tissue injury 1, 2
• Do NOT close infected wounds 2

When to Seek Immediate Medical Care

Call emergency services immediately if systemic symptoms develop, including: 1, 2

• Difficulty breathing, bronchospasm, or laryngospasm
• Muscle rigidity or severe muscle cramping
• Dizziness, confusion, or syncope
• Rapidly progressive swelling involving face, lips, tongue, or throat (angioedema)

Seek urgent medical evaluation if: 1, 2

• Pain extends beyond the bite site or becomes severe
• Pain is not controlled by over-the-counter medications
• An open wound develops
• Signs of infection appear (see below)

Antibiotic Management: A Critical Pitfall

The most common mistake is prescribing antibiotics for initial swelling—this is almost always unnecessary. Large swelling in the first 24-48 hours is caused by allergic inflammation and mediator release, NOT infection. 2

When Antibiotics ARE Indicated

Antibiotics should only be used when there is confirmed or highly suspected secondary bacterial infection, evidenced by: 2, 3

• Progressive erythema extending beyond the initial bite site
• Purulent discharge
• Systemic signs of infection (fever, elevated WBC count)
• Failure to improve after 24-48 hours despite appropriate wound care

Antibiotic Selection for Secondary Infection

If secondary bacterial infection is confirmed, empiric coverage must include MRSA activity, as 87% of infected spider bites grow methicillin-resistant Staphylococcus aureus. 3

First-line oral therapy: 2

• Trimethoprim-sulfamethoxazole OR
• Doxycycline

Alternative option: 2

• Clindamycin (if local resistance patterns permit)

This represents a critical departure from traditional penicillin-based therapy, which fails in the majority of cases due to community-acquired MRSA prevalence. 3

Management of Medically Significant Spider Bites

Black Widow (Latrodectus) Envenomation

Black widow bites produce minimal skin changes but cause severe neuromuscular symptoms. 4, 5

• Primary symptoms: muscle cramping, severe pain, and neuromuscular dysfunction 4, 5
• Treatment approach: 4, 6, 5
  • Analgesics for pain control
  • Benzodiazepines for muscle spasm
  • Calcium gluconate may provide relief
  • Antivenom is available but not widely accessible in the United States; consider for severe, refractory cases 5

Brown Recluse (Loxosceles) Envenomation

Brown recluse bites are frequently overdiagnosed and should be treated supportively. 5

• Dermonecrosis develops within 72-96 hours if it occurs at all 4
• Only rarely causes significant skin necrosis 5

Primary treatment: 4, 2

• Rest and ice compresses
• Over-the-counter analgesics
• Delayed surgical debridement (several weeks after bite, not immediate) 4, 2
• Dapsone may be considered for progressive necrosis 4

Systemic loxoscelism (rare): 4

• Presents with massive hemolysis and minimal skin changes
• May warrant systemic corticosteroids 4

Follow-Up and Recovery Timeline

• Most patients with local symptoms only recover completely within 24-48 hours 1, 2
• Continue pain management with over-the-counter medications as needed for several days 1, 2
• Follow-up within 24 hours by phone or office visit is advised 2
• Monitor for signs of secondary infection requiring prompt medical attention 1

Special Considerations for Surgical Management

For severe secondary infections requiring surgical intervention: 3

• Perform aggressive wide surgical debridement
• Obtain intraoperative wound cultures
• Initiate empiric antibiotics with MRSA coverage
• Adjust antimicrobial therapy based on culture and sensitivity results

The mean time to surgical evaluation in severe cases is 5 days, with 29% of patients having already failed outpatient penicillin-based therapy. 3