What antibiotic is used to treat spider bites?

Antibiotic Treatment for Spider Bites

For spider bites with signs of infection, amoxicillin-clavulanate (875/125 mg twice daily) is the preferred antibiotic treatment, though most spider bites do not require antibiotics unless secondary infection develops. 1

When to Seek Medical Care

Spider bites typically do not require immediate medical attention unless:

• Pain extends beyond the bite site or becomes severe 2
• An open wound develops 2
• Systemic symptoms develop (difficulty breathing, muscle rigidity, dizziness, confusion) 2
• Signs of secondary infection appear (increasing redness, warmth, pain, purulent drainage) 1

Initial Management of Spider Bites

1. Clean the wound thoroughly with soap and water 1
2. Apply ice for local pain relief 2
3. Consider over-the-counter pain medications:
   • Acetaminophen or NSAIDs for pain management 2
   • Topical lidocaine (if skin is intact) can help with pain 2

Antibiotic Treatment Algorithm

When to Start Antibiotics:

• Do not start antibiotics routinely for all spider bites
• Only initiate antibiotics when signs of infection are present:
  • Increasing redness, warmth, pain
  • Purulent drainage
  • Systemic symptoms (fever, chills)

First-line Antibiotic Options:

1. Amoxicillin-clavulanate: 875/125 mg twice daily 1

Alternative Options (for penicillin-allergic patients):

• Clindamycin: 300-400 mg three times daily 1
• Doxycycline: 100 mg twice daily (particularly when Pasteurella species are suspected) 1

Special Considerations

MRSA Concerns

Recent evidence shows that spider bite wounds with secondary infection often grow methicillin-resistant Staphylococcus aureus (MRSA) 3. In a study of 38 patients with infected spider bites requiring surgical debridement, 86.8% had MRSA infections 3. Therefore:

• Consider MRSA coverage for infected spider bites, especially if:
  • Patient has failed initial outpatient therapy with penicillin-based antibiotics
  • Local MRSA rates are high
  • Patient has risk factors for MRSA

For MRSA Coverage:

• Trimethoprim-sulfamethoxazole: 1-2 double-strength tablets twice daily 2, 3
• Doxycycline: 100 mg twice daily 2
• Clindamycin: 300-450 mg three times daily 2

Severe Infections

For rapidly spreading infections, significant pain/swelling, systemic toxicity, or deep tissue involvement:

• Consider inpatient management with IV antibiotics 1
• Surgical consultation may be needed for debridement 3

Specific Spider Considerations

Brown Recluse Spider (Loxosceles)

• Most bites resolve without aggressive therapy 4
• Treatment focuses on wound care and minor debridement 4
• Antibiotics only if secondary infection develops

Black Widow Spider (Latrodectus)

• Bites primarily cause muscle cramping and pain, not skin infections 4
• Treatment focuses on pain control, muscle relaxants, and calcium gluconate 5
• Antivenin may be needed in severe cases 4

Common Pitfalls to Avoid

1. Overdiagnosis of spider bites: Many "spider bites" are actually other conditions or insect bites
2. Unnecessary antibiotic use: Most spider bites do not require antibiotics unless secondary infection develops
3. Inadequate coverage for MRSA: When infection is present, consider local MRSA prevalence when selecting antibiotics
4. Delayed surgical consultation: Severe infections may require debridement in addition to antibiotics

Remember to monitor the bite site for 48-72 hours for signs of infection progression, with follow-up within 24-48 hours to assess treatment response 1.