When should antibiotics be prescribed for a bug bite?

Antibiotic Prescription for Bug Bites

Antibiotics should NOT be prescribed routinely for uncomplicated insect bites but should be reserved for specific circumstances showing signs of infection or in high-risk patients. 1, 2

When to Prescribe Antibiotics

Indications for Antibiotic Therapy

• Signs of infection:
  • Progressive redness extending beyond the initial bite area
  • Increasing pain and swelling after 48 hours
  • Warmth and tenderness at the site
  • Purulent discharge
  • Lymphangitis (red streaking)
  • Fever or systemic symptoms
  • Regional lymphadenopathy

High-Risk Patients Who May Need Prophylactic Antibiotics

• Immunocompromised individuals
• Asplenic patients
• Patients with advanced liver disease
• Bites in high-risk locations (hands, face, genitals, areas near joints) 2
• Moderate to severe injuries from bites 1

Special Considerations for Specific Bites

Tick Bites

• Lyme Disease Prophylaxis: Single dose of doxycycline (200 mg for adults, 4.4 mg/kg up to 200 mg for children) if ALL criteria are met 1:
  1. Identified Ixodes spp. tick
  2. Tick attached ≥36 hours
  3. Bite occurred in highly endemic area for Lyme disease
  4. Antibiotic can be started within 72 hours of tick removal

Animal and Human Bites

• Higher infection risk (30-50% of cat bites, 5-25% of dog bites, 20-25% of human bites) 1
• Require antibiotic therapy more frequently than insect bites
• Amoxicillin-clavulanate is first-line therapy (875/125 mg twice daily) 1, 2

Antibiotic Selection When Indicated

First-Line Options

• Uncomplicated cellulitis:
  • Cephalexin 250-500 mg four times daily
  • Dicloxacillin 500 mg four times daily
  • Flucloxacillin (in UK settings) 3

For Penicillin-Allergic Patients

• Clindamycin 300-400 mg three times daily 2
• Doxycycline 100 mg twice daily (particularly effective for certain bites) 2

For Suspected MRSA

• Consider MRSA coverage in areas with high prevalence or if patient has risk factors 4
• Trimethoprim-sulfamethoxazole 160/800 mg twice daily
• Doxycycline 100 mg twice daily

Duration of Therapy

• 5-7 days for uncomplicated infections
• 10-14 days for more severe infections or immunocompromised patients

Common Pitfalls to Avoid

1. Overprescribing antibiotics for simple insect bites

   • Research shows antibiotics are likely overused for insect bites, contributing to antimicrobial resistance 3
   • Up to 74% of patients with insect bites receive antibiotics despite many not showing signs of infection 3

2. Confusing inflammatory reactions with infection

   • Normal inflammatory reactions to insect bites can mimic early cellulitis
   • Consider antihistamines first for itchy, red, but non-progressive lesions 5, 6

3. Missing MRSA infections

   • In some regions, MRSA is increasingly common in skin infections following spider bites 4
   • Consider MRSA coverage if local prevalence is high or if initial therapy fails

4. Neglecting non-antibiotic management

   • Cold compresses, oral antihistamines, and topical corticosteroids should be first-line for uncomplicated bites 1, 2
   • Only 22% of patients take antihistamines before consulting despite 45% complaining of itch 3

Monitoring and Follow-up

• Advise patients to return if:
  • Symptoms worsen despite 48 hours of antibiotics
  • Fever develops or increases
  • Redness or swelling continues to spread
  • New symptoms develop

By following these guidelines, clinicians can ensure appropriate antibiotic stewardship while effectively treating truly infected insect bites and preventing complications in high-risk patients.