What are the next steps for a patient with a skin infection that has not responded to Keflex (cephalexin) and then doxycycline, with continued redness?

Management of Persistent Skin Infection After Cephalexin and Doxycycline Treatment

For a skin infection with persistent redness after failed treatment with cephalexin and doxycycline, the next steps should include obtaining bacterial cultures, considering MRSA coverage with trimethoprim-sulfamethoxazole or clindamycin, and possible incision and drainage if a purulent collection is present.

Assessment of Treatment Failure

Evaluate for MRSA

• Cephalexin is not effective against MRSA, which is a common cause of community-acquired skin infections 1
• Persistent redness after sequential treatment with cephalexin and doxycycline suggests possible MRSA infection or another resistant organism 1
• Obtain bacterial cultures from the affected area to guide targeted antibiotic therapy 2

Consider Other Resistant Organisms

• Extended-Spectrum β-Lactamase (ESBL) producing organisms are also not covered by cephalexin 1
• Secondary infections with Staphylococcus aureus are the most frequently detected infectious agents in persistent skin infections 2

Next Treatment Steps

Immediate Actions

1. Obtain bacterial cultures before initiating new antibiotics if possible 2
2. Consider incision and drainage if there is any purulent collection, as this is the primary treatment for purulent infections 1
3. Start empiric MRSA coverage while awaiting culture results 1

Antibiotic Options for MRSA Coverage

• Trimethoprim-sulfamethoxazole (TMP-SMX) is recommended for MRSA coverage 1
• Clindamycin 300-450mg three times daily for 5-6 days is an alternative option 1
• For severe infections, consider vancomycin 15-20 mg/kg IV every 8-12 hours 1

Duration of Treatment

• For mild-to-moderate infections: 5-6 days 1
• For severe infections: 10-21 days 1
• Extend duration based on clinical response, especially in immunocompromised patients 1

Special Considerations

Cross-Reactivity Concerns

• If the patient had an allergic reaction to cephalexin, be aware of potential cross-reactivity with other beta-lactams 2
• Cephalexin shares side chains with amoxicillin, which may increase risk of cross-reactivity in patients with IgE-mediated allergies 2

Monitoring Response

• Clinical improvement should be expected within 72 hours of starting appropriate therapy 1
• If no improvement is seen within 72 hours, reevaluate the treatment plan 1

Supportive Measures

• Apply warm compresses to the affected area 3-4 times daily 1
• Elevate the affected area to reduce edema 1
• Ensure adequate pain control 1

Prevention of Recurrence

• Address predisposing factors such as tinea pedis, edema, obesity, and venous insufficiency 1
• Good personal hygiene practices including daily change of socks and careful drying between toes after showers 2
• Avoid sharing towels or equipment 2

Remember that persistent skin infections after multiple antibiotic courses require careful evaluation for resistant organisms and may need more aggressive management strategies.