What is the next treatment step for a patient with cellulitis of the right lower leg who has not responded to Keflex (Cephalexin)?

Management of Cellulitis Not Responding to Cephalexin

For a patient with cellulitis of the right lower leg who has not responded to Keflex (cephalexin), the next treatment step should be switching to a broader-spectrum antibiotic such as trimethoprim-sulfamethoxazole, clindamycin, or linezolid, depending on local MRSA prevalence and patient factors.

Assessment of Treatment Failure

When cellulitis fails to respond to initial cephalexin therapy, several factors should be considered:

1. Potential pathogens:

   • Methicillin-resistant Staphylococcus aureus (MRSA) is a common cause of treatment failure
   • Beta-hemolytic streptococci may be resistant to the initial therapy
   • Mixed infections may be present

2. Evaluation for complications:

   • Deep abscess formation
   • Underlying osteomyelitis
   • Inadequate source control
   • Vascular insufficiency

Next Treatment Options

For Outpatient Management:

• First alternative option:

  • Clindamycin 300-450 mg orally four times daily 1
  • Effective against both MRSA and streptococci
  • Consider if moderate infection without systemic symptoms

• Second alternative option:

  • Trimethoprim-sulfamethoxazole (TMP-SMX) 1-2 double-strength tablets twice daily 1
  • Particularly effective against community-acquired MRSA
  • May be less effective against streptococci alone

• Third alternative option:

  • Linezolid 600 mg orally twice daily 2, 1
  • For more severe cases or treatment failures
  • Expensive but highly effective against MRSA

For Inpatient Management (if needed):

• For severe infections requiring IV therapy:
  • Vancomycin (dosing based on weight and renal function) 2, 1
  • Daptomycin (with or without aztreonam) 2
  • Linezolid IV 600 mg twice daily 2

Supportive Measures

• Elevation of the affected limb to promote gravity drainage of edema and inflammatory substances 2
• Proper wound care including cleansing and debridement of any necrotic tissue 2
• Off-loading pressure on the affected area 2
• Address underlying conditions that may predispose to infection (e.g., tinea pedis, venous insufficiency) 2

Duration of Therapy

• For moderate infections, 10-14 days of therapy is typically recommended 2
• Consider longer duration (2-4 weeks) if there is delayed response or deeper tissue involvement 2

Common Pitfalls to Avoid

1. Failure to recognize deeper infection such as abscess or osteomyelitis
2. Inadequate source control (e.g., not draining collections if present)
3. Insufficient elevation of the affected limb
4. Overlooking predisposing conditions like tinea pedis or venous stasis
5. Premature discontinuation of antibiotic therapy

Special Considerations

• If the patient has diabetes, consider diabetic foot infection protocols which may require more aggressive management and broader spectrum antibiotics 2
• Consider obtaining wound cultures before changing antibiotics, especially if MRSA is suspected 2, 1
• If there is no improvement after the second antibiotic regimen, consider hospitalization for IV antibiotics and further evaluation 2

Remember that cephalexin has been shown to be ineffective for certain infections like Lyme disease that may initially present similar to cellulitis 3, so consider alternative diagnoses if the presentation is atypical.