What is the typical dosing for cephalexin (Keflex) for skin infections?

Cephalexin Dosing for Skin Infections

For adult skin infections, prescribe cephalexin 500 mg orally four times daily (every 6 hours) for 7-10 days, with 7 days being typical for most uncomplicated cases. 1, 2, 3

Standard Adult Dosing

• 500 mg orally every 6 hours (four times daily) is the recommended dose for most skin and soft tissue infections including cellulitis, wound infections, and impetigo 1, 2, 3
• Treatment duration is typically 7 days, extended to 10 days based on clinical response 1, 2, 3
• Maximum daily dose is 4 grams per day 1, 4
• The FDA label allows 500 mg every 12 hours for uncomplicated skin infections, but IDSA guidelines favor the four-times-daily regimen for more reliable coverage 4, 1

Pediatric Dosing

• 25-50 mg/kg/day divided into 4 doses for children weighing less than 40 kg 3, 4
• Can be administered every 12 hours for streptococcal infections and uncomplicated skin infections 4
• Duration is 7-10 days depending on clinical response 3

When Cephalexin is Appropriate

• Non-purulent cellulitis without systemic signs of infection 1
• Methicillin-susceptible Staphylococcus aureus (MSSA) and streptococcal infections 1, 2, 3
• Impetigo caused by Staphylococcus and Streptococcus species (250 mg four times daily for adults) 2
• Penicillin-allergic patients without immediate hypersensitivity reactions 1, 3
• Surgical site infections (500 mg every 6 hours) 2

Critical Pitfalls to Avoid

Do NOT Use Cephalexin For:

• Purulent infections with suspected MRSA - instead use trimethoprim-sulfamethoxazole, doxycycline, or clindamycin 1, 2, 3
• Patients with MRSA risk factors: purulent drainage, systemic signs, history of MRSA colonization, injection drug use, or failed initial antibiotic therapy 1
• Necrotizing infections - these require broad-spectrum IV antibiotics and urgent surgical intervention 1
• Cephalexin has no activity against MRSA despite some older studies showing clinical response (likely due to incision and drainage, not the antibiotic) 2, 3, 5

Clinical Monitoring

• Expect clinical improvement within 48-72 hours of starting therapy 3
• If no improvement by 72 hours, consider alternative diagnoses, resistant organisms (particularly MRSA), or need for incision and drainage 3, 6
• Complete the full 7-day course even if symptoms improve earlier 3

Special Populations

• Pregnancy: FDA category B, generally considered safe 3
• Renal impairment: Dose adjustment required (not specified in provided evidence, but standard practice)

Practical Advantages

• Cephalexin offers less frequent dosing compared to dicloxacillin and is available in suspension formulation 1
• Equivalent efficacy to other first-generation cephalosporins like cefazolin when oral therapy is appropriate 1, 6
• Well-tolerated with diarrhea (4-10%) being the most common adverse effect 5, 7