What antibiotic is predominantly used for skin infections and cellulitis?

First-Line Antibiotics for Skin Infections and Cellulitis

Cephalexin is the predominant antibiotic used for skin infections and cellulitis, particularly for uncomplicated cases targeting Gram-positive bacteria like Streptococcus and Staphylococcus aureus. 1, 2

Antibiotic Selection Algorithm

First-Line Options:

• Cephalexin: 500 mg orally 3-4 times daily for 5-6 days 2, 3
  • Gold standard for uncomplicated cellulitis
  • Effective against streptococci and methicillin-sensitive Staphylococcus aureus
  • Achieves cure rates of 90% or higher 4

Alternative First-Line Options:

• Clindamycin: 300-450 mg orally three times daily for 5-6 days 2, 5
  • Particularly useful for penicillin-allergic patients
  • Provides coverage against MRSA, streptococci, and anaerobes
  • Note: Risk of Clostridioides difficile infection

Special Situations Requiring Alternative Coverage:

1. MRSA Risk Factors (prior MRSA infection, frequent hospitalizations):

   • Add trimethoprim-sulfamethoxazole or switch to clindamycin 2
   • Note: Studies show adding trimethoprim-sulfamethoxazole to cephalexin did not significantly improve outcomes in uncomplicated cellulitis 6, 7

2. Healthcare-Associated Infections:

   • Broader coverage with piperacillin-tazobactam or a carbapenem plus oxacillin 2

3. Immunocompromised Patients:

   • Broader spectrum coverage and potentially longer duration 2

Treatment Duration and Monitoring

• Standard treatment duration: 5-6 days for uncomplicated cases 2
• Expect clinical improvement within 48-72 hours of starting appropriate therapy
• If no improvement after 72 hours:
  1. Reevaluate diagnosis
  2. Consider changing antibiotic therapy
  3. Evaluate for abscess formation requiring drainage 2

Management of Abscesses

• Incision and drainage is the primary treatment for abscesses 1, 2
• Antibiotics alone are insufficient for abscess treatment
• Simple abscesses may not require antibiotics after adequate drainage 1

Common Pitfalls to Avoid

1. Overuse of MRSA coverage in areas with low MRSA prevalence
2. Failure to distinguish between cellulitis and pseudocellulitis
3. Inadequate duration of treatment (too short or unnecessarily long)
4. Not elevating affected limbs to reduce swelling
5. Missing underlying predisposing factors that may cause recurrence
6. Failing to perform incision and drainage when abscesses are present 2

Special Populations

• Children: Cephalexin dosing is 25-50 mg/kg/day divided into 4 doses 3

  • For otitis media, higher dosing of 75-100 mg/kg/day may be required
  • For streptococcal infections, treat for at least 10 days

• Pregnant/Breastfeeding Women:

  • Cephalexin is generally safe
  • Avoid doxycycline in pregnant women (especially third trimester) 2
  • Breastfeeding can continue during treatment for mastitis 2

Cephalexin remains the cornerstone of treatment for uncomplicated skin infections and cellulitis, with alternatives available for special situations and patient-specific factors.